Lost Continent

We’ve all heard of Atlantis, which was a ‘continent’ or at least a city that reportedly sank into the ocean due to some natural disaster. Every few years, there is some report in the news of the latest theory about where that continent or city was located.

When I was considerably younger, I read at least one book about the lost continent of Lemuria. I keep wanting to say the book I read was written by Lin Carter, who did write about Lemuria (before it sank into oblivion), but it was so long ago that the name of the continent is all I remember. Nowadays, Wikipedia says that a lost continent called Lemuria was proposed in 1864 by zoologist Philip Sclater, who theorized it was located in the Indian Ocean. The idea was debunked in the 20^th century once scientists understood plate tectonics and continental drift.

But a team of scientists really have discovered a lost continent now, which they are calling Zealandia. Most of it is underwater, but New Zealand and some other islands stand up far enough to be above the ocean. Zealandia is more than half the size of Australia, and it extends northwest and southeast of the New Zealand islands.

It was a part of Gondwana when that supercontinent existed, but when it started to break apart, Zealandia was one of the parts, breaking away around 81 million years ago. Then 95% of that part, Zealandia, sank beneath the waves.

The scientists have finished mapping Zealandia recently after 20 years of work, and they state that it contains a vast array of diverse rocks that proves it is made of continental crust, so it is not just a section of seafloor.

Zealandia is sometimes referred to as Earth’s 8^th continent.

 

https://en.wikipedia.org/wiki/Zealandia

https://www.msn.com/en-us/news/technology/scientists-finally-finished-mapping-earth-s-8th-continent-zealandia-helping-them-solve-the-lost-continent-s-mysterious-history/ar-AA1hu1QE?ocid=mailsignout&pc=U591&cvid=71bd9ad3ca8b4b63b9e2633f4f699f75&ei=36#image=AA1bYYe9|1

Jurassic Park Period Part 7

 Fauna - All the rest of it

 Insects and arachnids - There appears to have been no major extinction of insects at the Triassic–Jurassic boundary. Many important insect fossil localities are known from the Jurassic of Eurasia. The diversity of insects stagnated throughout the Early and Middle Jurassic, but during the latter third of the Jurassic, origination rates increased substantially while extinction rates remained flat. The increasing diversity of insects in the Middle–Late Jurassic corresponds with a substantial increase in the diversity of insect mouthparts. The Middle to Late Jurassic was a time of major diversification for beetles. Weevils first appear in the fossil record during the Middle to Late Jurassic, but are suspected to have originated during the Late Triassic to Early Jurassic. The oldest known lepidopterans (the group containing butterflies and moths) are known from the Triassic–Jurassic boundary. Modern representatives of both dragonflies and damselflies also first appeared during the Jurassic. Although modern representatives are not known until the Cenozoic, insects thought to represent primitive relatives of modern fleas are known from the Middle Jurassic of Asia. These insects are substantially different from modern fleas, because they lack the specialized morphology and they were larger. The earliest group of stick insects first appeared during the Middle Jurassic.

Spiders diversified through the Jurassic, and several long names of species or orders were given in the article. But to me, a spider is a spider. The oldest member of the family Archaeidae is known from the Middle Jurassic of China. Mongolarachne from the Middle Jurassic of China is among the largest known fossil spiders, with legs over 5 centimetres (2 inches) long. I know I've seen granddaddy longlegs with longer legs, but maybe they are not true spiders. It's been a long time since I had the opportunity to count their legs.

Birds - The earliest avialans (birds and their ancestors) appear during the Middle to Late Jurassic. There are some examples from China that have been postulated to have been birds, but have alternatively been found to be a separate lineage of another group of animal altogether. So not only were there birds, but also animals that may or may not have been birds.

Mammals - Mammals originated from cynodonts at the end of the Triassic. Cynodonts were a group of creatures that measured up to 1.5 metres (4.5 feet) in length, and that did include a tail. They may have eaten roots, insects, eggs, and possibly even small or infant dinosaurs. As mammals, they diversified extensively during the Jurassic. While most Jurassic mammals are solely known from isolated teeth and jaw fragments, exceptionally preserved remains have revealed a variety of lifestyles. Some were adapted to aquatic life, similar to the platypus and otters. Some members had a patagium akin to those of flying squirrels, allowing them to glide through the air. One aardvark-like mammal was likely a specialist on colonial insects, similar to living anteaters.

Early relatives of monotremes first appear in the Middle Jurassic of Gondwana. The monotremes are a group of highly specialized egg-laying predatory mammals, containing the platypus and echidnas. There are only five living species of monotreme, contained within two families.

Therian mammals, represented today by living placentals and marsupials, appear during the early Late Jurassic, represented by Juramaia, a mammal closer to the ancestry of placentals than marsupials. Juramaia is much more advanced than expected for its age, as other therian mammals do not appear until a later period.

Two groups of non-mammalian cynodonts persisted beyond the end of the Triassic. One ate insects and has a few records from the Early Jurassic. A herbivorous group of cynodonts has abundant records from the Jurassic, overwhelmingly from the Northern Hemisphere.

Sounds like life was all over the planet, much like it is today. Possibly not quite as diverse as it is today. If we could keep the herbivores out of our crop fields, it might be possible to colonize. And we should be able to hunt, to put meat on the table. I'm a little worried about that, though. If we killed the wrong mammal, would we disrupt the evolutionary trail that would result in humans?

Well, we'd never know about it. There's millions of years between the Jurassic Period and the development of anything resembling humans. There's several possibilities here, that I see. Either our colony would thrive, establishing a new timeline of humans on Earth. By the time 'modern day' came around, we may have taken off for outer space. In which case, we would either all leave and Earth would be devoid of humans. Or not everybody left, and the civilization continued strong, so Earth would have humans, even though it was a mixed-up mess as to how we evolved, showing up so abruptly in the Jurassic. Or at some point, our little piece of civilization would sputter and die, and there would be no humans any more, and who would be here to miss them? Or our civilization would die, and humans would evolve, lending a whole new meaning to the term 'Circle of Life'.

Okay, so we'll take a vote. Everybody in favor of settling down here in the Jurassic Period and establishing a colony, say 'Aye'.

Jurassic Park Period Part 6

 Fauna - Amphibians & Land Animals

Amphibians - The Early Jurassic Prosalirus is thought to represent the first frog relative capable of hopping like living frogs. Recognizable frogs like the South American Notobatrachus are known from the middle of the Jurassic. Although salamander-like amphibians are known from the Triassic, salamander ancestors first appeared during the Jurassic.

But most of the land animals mentioned were dinosaurs. Dinosaurs had morphologically diversified in the Late Triassic, but experienced a major increase in diversity and abundance during the Early Jurassic after the extinction of other reptile groups, becoming the dominant vertebrates in terrestrial ecosystems.

Theropods - Theropods are a group of dinosaurs that had hollow bones and 3 claws on each appendage. They first appeared in the Late Triassic. One group, called the Neotheropoda, persisted into the Early Jurassic. The earliest 'bird snout' members of the averostrans appear during the Early Jurassic and continue throughout the rest of that period and the Jurassic. Most theropods were carnivorous, although the unusual Limusaurus of China had a herbivorous diet, with adults having beaked jaws, making it the earliest known theropod to have converted from an ancestrally carnivorous diet. The Coelurosaurs first appeared during the Middle Jurassic, including early tyrannosaurs such as Proceratosaurus. The scansoriopterygids was a group of small feathered coelurosaurs with membraneous, bat-like wings for gliding, and records have been found from the Middle to Late Jurassic.

Ornithischians - This refers to an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. Hence they were called "bird-hipped", or Ornithischia. However, birds are only distantly related to this group, as birds belong to the theropod line of dinosaurs. The Ornithischians included those known as "horn-faced", such as Triceratops, and the armored dinosaurs such as stegosaurs and ankylosaurs. There is strong evidence that certain groups of ornithischians lived in herds, possibly segregated by age. Some were at least partially covered in hair- or feather-like pelts, and there is much debate of whether these pelts may have been primitive feathers.

The earliest definitive ornithischians appear during the Early Jurassic. The earliest Ankylosauria and Stegosauria appear during the Middle Jurassic. At least some ornithischians were covered in protofeathers.

Sauropodomorphs - Sauropods are a group of "lizard-hipped" dinosaurs. They had long necks and tails, small heads and 4 huge, pillar-like legs. They became the dominant large herbivores in terrestrial ecosystems during the Jurassic. Some reached gigantic sizes, becoming the largest organisms to have ever lived on land. Bipedal sauropodomorphs continued to exist into the Early Jurassic, but went extinct by the beginning of the Middle Jurassic. Quadrupedal sauropomorphs were a hold-over from the Late Triassic. One type of quadrupedal from the earliest Jurassic of South Africa reached an estimated weight of 12 tons, far in excess of other known sauropodomorphs.

So it appears there were lots and lots of dinosaurs ambling across the landscape. I know I earlier said we would pause to look at some of the better-known dinosaurs, but I didn't realize how many episodes the Jurassic Period would take, just to give it this brief look. So I've changed my mind, and the next episode (all the rest of the fauna) will finish up the Jurassic Period before I go on to the next time period in the history of the Earth. Later on, when I've finished the Earth's prehistory, I'll find a time to take a look at various species of dinosaurs, so keep watching, because I'll get to them!

Jurassic Park Period Part 2

Paleoclimate

Climate during the Jurassic was approximately 5-10 degrees C (41-50 degrees F) hotter than present time, with atmospheric carbon dioxide likely 4 times higher. It's likely that forests grew near the poles, where they experienced warm summers and cold, sometimes snowy winters. It is unlikely there were any ice sheets, as the high summer temperatures would have prevented the accumulation of snow, although there may have been mountain glaciers. The ocean depths were likely 8 degrees C (about 46 degrees F) warmer than present, and coral reefs grew further north and south by 10 degrees of latitude There were probably large areas of desert in the lower latitudes.

The beginning of the Jurassic was probably marked by a thermal spike corresponding to the eruption of the Central Atlantic magmatic province. This was followed by the Early Jurassic cool interval between 199 and 183 million years ago. ('Cool', of course, is a relative term.) Then came a spike in global temperatures of around 4-8 degrees C (39-46 degrees F) during the eruption of the Karoo-Ferrar large igneous provinces in southern Gondwana, which lasted from 183 million years ago until 174 million years ago.

During this long temperature spike, the ocean surface temperatures likely exceeded 30°C (86°F) and all the land mass between 30°N to 30°C were likely extremely arid, with temperatures in the interior in excess of 40°C (104°F).

There was an episode of widespread oceanic anoxia that is often attributed to the eruption of the Karoo-Ferrar large igneous provinces and the associated increase of carbon dioxide concentration in the atmosphere. This event had significant impact on marine invertebrates, but little effect on marine reptiles. During this time, the Sichuan Basin (of southwestern China) was transformed into a giant lake, 3 times the size of Lake Superior. Seawater pH dropped to its lowest point around the middle of this event.

This was followed by a (relatively) cool period between 174 and 164 million years ago, which was followed by a warm interval between 164 and 150 million years ago. During this warm interval, the land mass interior had less severe seasonal swings than before because the expansion of the Central Atlantic and the western Indian Oceans provided new sources of moisture to moderate the temperature. The end of the Jurassic was marked by another cool interval, which began 150 million years ago and continued beyond the end of the Jurassic.

I recently saw someone on social media poo-pooing concern over the climate changing. As they put it, the climate has been changing for millions of years. And they are right, it has been. What they fail to take into consideration is that mass extinction events have been happening for millions of years, AND the climate changes of the past have not occurred as rapidly as this one. If we want to survive this climate change, we need to use the brains we have.

https://en.wikipedia.org/wiki/Jurassic

Jurassic Park Period Part 1

 

Paleogeography

Everybody knows about dinosaurs, right? And thanks to the Jurassic Park series of movies, we all know the dinosaurs lived during the Jurassic Period. But what else is noteworthy about this geologic period? I'll try to uncover something other than various dinosaurs to study.

However, I am just as fascinated with dinosaurs as any little kid, so I'll spend some time studying some of our favorites while I'm at it.

The Jurassic Period started 201.3 million years ago and ended approximately 145 million years ago. There was, as seems so common with these geological periods, an extinction event at the dividing point between the Triassic and Jurassic Periods.

The Triassic/Jurassic extinction event seemed to be caused by the Central Atlantic Magmatic Province, which, as best I can figure out, means a lot of magma and lava was moving around in the areas currently known as northwestern Africa, southwestern Europe, southeastern North America and Northeastern South America.

The articles I read seemed to indicate that this was not just a matter of volcanic activity, that some of it could have been caused by the action of diverging plate tectonics. We are aware of the Atlantic rift, where two tectonic plates are moving away from each, allowing a large volume of magma to flow, but this is not considered a volcano. This magma movement began about 201 million years ago, and continued for about 600,000 years. It was the largest activity of this type known to man, covering roughly 11 million km².

By the beginning of the Jurassic, the supercontinent Pangaea had begun rifting into two landmasses: Laurasia to the north and Gondwana to the south. The rifting between North America and Africa was the first to happen, in conjunction with the Central Atlantic Magmatic Province

By the beginning of the Jurassic, there was flooding in most parts of central and western Europe, transforming it into an archipelago of islands surrounded by shallow sea. Beginning in the Early Jurassic, the proto-Atlantic was expanded by the "Viking Corridor" (or Transcontinental Laurasian Seaway) which stretched between the Baltic Shield and Greenland, and was several hundred kilometers wide. All during the Jurassic, the North Atlantic Ocean remained relatively narrow, while the South Atlantic did not open until later.

At the beginning of the Jurassic, North and South America remained connected, but at some point, they rifted apart to form the Caribbean Seaway, which connected the north Atlantic Ocean with what is now called the Pacific Ocean, although it was much larger back then, taking up over half the globe and was called the Panthalass Ocean.

About 183 million year ago, another magmatic event started, the Karoo-Ferrar event, this one in South Africa and Antarctica. This triggered another extinction event by causing widespread oceanic anoxia, ocean acidification and elevated temperatures. I am uncertain if these types of conditions were responsible for the Triassic/Jurassic extinction event.

Madagascar and Antarctica rifted away from Africa in association with the eruption of the Karoo-Ferrar large igneous provinces, which opened the western Indian Ocean and began the fragmentation of Gondwana.

During the Middle to Late Jurassic, the Sundance Seaway, a shallow inland sea, covered much of northwest North America.

The sea level rose and fell many times during the Jurassic, peaking at one point as high as 140 meters (462 feet) above the present level.

Wow! So much happening! And that's just the geography! This makes me wonder what else was going on!

https://en.wikipedia.org/wiki/Jurassic

https://en.wikipedia.org/wiki/Central_Atlantic_magmatic_province

https://en.wikipedia.org/wiki/Large_igneous_province

Triassic Period Part 2

 Now let's take a look at the inhabitants of the Triassic Period.

Three categories of organisms can be distinguished in the Triassic record: survivors from the Permian–Triassic extinction event, new groups which flourished briefly, and other new groups which went on to dominate the Mesozoic Era.

To go back to the beginning, after the extinction event just before the Triassic Period began, the Earth's biosphere was impoverished. It was well into the middle of the Triassic before life recovered its former diversity. Therapsids (including what would become mammals) and archosaurs (including crocodilian reptiles) were the chief terrestrial vertebrates of this period. A specialized subgroup of archosaurs, called dinosaurs, first appeared late in the Triassic, but did not become dominant until the succeeding Jurassic Period.

The first true mammals also evolved during this period, as well as the first flying vertebrates, the pterosaurs, who were a specialized subgroup of archosaurs.

In marine environments, new types of corals appeared in the Early Triassic, forming small patches of reefs of modest extent compared to the great reef systems of modern times. The shelled ammonites (whose shell resembled that of the modern nautilus, but is not an ancestor) recovered, diversifying from a single line that survived the Permian-Triassic extinction.

The fish fauna was remarkably uniform, with many families and genera exhibiting a global distribution in the wake of the mass extinction event. There were also many types of marine reptiles. The first of the lizard-like animals appeared in the Early Triassic seas and soon diversified, and some developed to huge size during the Late Triassic.

On land, the surviving plants included ginkos, ferns, and horsetails, among others. Seed plants came to dominate the terrestrial flora. In the northern hemisphere, conifers and ferns flourished. A seed fern genus would dominate Gondwana throughout the period.

Many groups of terrestrial fauna appeared in the Triassic period or achieved a new level of evolutionary success during it. They include lungfish, Temnospondyls (early amphibians that had mostly been replaced by reptiles, they made a come-back in this period), Rhynchosaurs (the primary large herbivores in many Triassic ecosystems), Phytosaurs (looked like crocodiles, but unrelated), Aetosaurs (heavily armored and mostly herbivorous), Rauisuchians (the keystone predators of most Triassic terrestrial ecosystems), Theropods (dinosaurs but not the large kind that would come later; most were 1-2 meters long), and Cynodonts (a large group that includes true mammals, complete with hair and a large brain).

Some amphibians were among those groups that survived the Permian-Triassic extinction event. The first ancestors of frogs are known from the Early Triassic, but did not become common until the Jurassic (which comes next).

Among reptiles, the earliest turtles appeared during the Late Triassic Period.

During the Triassic, archosaurs displaced therapsids as the dominant amniotes. This may have contributed to the evolution of mammals by forcing the surviving therapsids and their mammalia-form successors to live as small, mainly nocturnal insectivores. Nocturnal life may have forced the mammaliaforms to develop fur and a higher metabolic rate.

Though the end-Triassic extinction event was not equally devastating in all terrestrial ecosystems, several important clades of large reptiles disappeared, as did most of the amphibians, groups of small reptiles, and others (except for the proto-mammals). Some of the early, primitive dinosaurs also became extinct, but more adaptive ones survived into the Jurassic. Surviving plants that went on to dominate the Mesozoic Era included modern conifers.

The cause of the Late Triassic extinction in uncertain. It was accompanied by huge volcanic eruptions that occurred as the supercontinent Pangaea began to break apart about 202 to 191 million years ago, forming one of the largest known inland volcanic events since the planet had first cooled and stabilized. Another possible but less likely cause for the extinction event might be global cooling.

 

 

https://en.wikipedia.org/wiki/Triassic

Mesozoic Era

 Okay, we're going to take a quick overview look at the Mesozoic Era, also known as the Age of Reptiles. It lasted from 252 to 66 million years ago. It has 3 Periods nestled within it; the Triassic, Jurassic and Cretaceous periods. It was characterized by dinosaurs, conifers and ferns, a hot greenhouse climate, and the tectonic break-up of Pangaea.

The Mesozoic began just after the largest well-documented mass extinction in Earth's history, and it ended with another extinction event.

During this era, the supercontinent Pangaea broke into separate landmasses that would eventually move into their current positions during the following era. There was not much mountain building during this era, but what little did occur took place around what is now known as the Arctic Ocean. In contrast, the supercontinent Pangaea gradually split into a northern continent, Laurasia, and a southern continent, Gondwana. (Seems like this name has been used before.) By the end of the era, the continents had split up and some had rejoined into their present forms, though not their present positions. Laurasia became North America and Eurasia, while Gondwana split into South America, Africa, Australia, Antarctica and the Indian subcontinent, which would eventually slam into Asia, giving rise to the Himalayas, but not during this Era.

The climate varied, alternating between warm and cool periods. Overall, the Earth was hotter than it is today. The Triassic (first) Period was generally dry and highly seasonal, especially in Pangaea's interior. Low sea levels would have exacerbated temperature extremes. Pangaea's interior probably included expansive deserts.

Sea levels began to rise during the Jurassic (second) Period, most likely caused by seafloor spreading. The sea levels could have risen as much as 656 ft (200 m) above today's sea level. This would have flooded coastal area. In addition, the breaking up of Gondwana into smaller continents created new shorelines. Temperatures continued to increase for a time, then began to stabilize. With the proximity of water, humidity also increased, and the deserts retreated.

The climate of the Cretaceous (third) Period is more widely disputed. Probably, higher levels of carbon dioxide in the atmosphere could have almost eliminated the north-south temperature gradient, meaning that temperatures were about the same across the planet, about 10 degrees Centigrade higher than today.

Dinosaurs first appeared mid-way through the first period, and became the dominant terrestrial vertebrates by early in the second period, then died out at the end of the third period. Archaic birds appeared during the 2nd period (Jurassic), evolving from a branch of dinosaurs. True birds appeared in the third period. Mammals also appeared during this era, but they remained small (less than 33 lb) until the third period. Flowering plants appeared early in the third period and rapidly diversified, replacing conifers and other gymnosperms as the dominant group of plants. But we'll take a closer look at flora and fauna as we get to those periods.

 

https://en.wikipedia.org/wiki/Mesozoic

Permian Period Part 1

 The Permian Period is the last period of the Paleozoic Era, and it spans the 47 million years from 298.9 million years ago to 251.9 million years ago.

The Permian witnessed the diversification of two groups, the mammals (and all creatures more closely related to mammals than to reptiles and birds) and the reptiles. But I'm going to look at the conditions existing on the Earth at the time before I consider the animals that populated it.

At the time, the world was dominated by the supercontinent Pangaea, which formed when Euramerica and what was left of Gondwana collided during the Carboniferous. There was a smaller continent that lay to the northeast of Pangaea called Angara. There were also some small islands east of Pangaea called Cathaysia. Of course, with most of the land mass gathered into one supercontinent, the rest of the globe was ocean. The superocean of the time was the Panthalassa. Pangaea straddled the equator and reached for the poles (but didn't necessarily get there). This, of course, had an effect on the ocean currents of the time.

Early in this time period, Cimmeria—a string of microcontinental islands—tore off from the Gondwana area in the Southern Hemisphere and during the course of the period, moved up to join the Eurasian part of Pangaea in the Northern Hemisphere. Cimmeria included parts of today's Turkey, Iran, Afghanistan, Tibet and the Malay Peninsula. The Central Pangean Mountains, which began forming due to the collision of Laurasia and Gondwana during the Carboniferous Period, reached their maximum height shortly after the beginning of the Permian, and would have been comparable to the present Himalayas.

The Carboniferous rainforest collapse left behind vast regions of desert stretching over the continental interior. From approximately 262 million years ago to 259 million years ago, a series of volcanic erruptions in what is now China (was then part of Pangaea) led the way to an extinction event. This was compounded when a similar series of volcanic activity over a wide swath of Siberia (then located in Angara) continued to change the atmosphere. This mass extinction event ended the Permian Period, and started the next period. It was the largest mass extinction in Earth's history, with nearly 81% of marine species and 70% of terrestrial species dying. On land, it took 30 million years into the next time period for the ecosystems to recover.

Sea levels were mostly stable during the Permian, at several tens of meters (yards) above the present level. There was a sharp drop at one point, producing the lowest sea level of the entire Palaeozoic Era, roughly the same as today's level.

At the start of the Permian, the Earth was still in an icehouse. Around 323 million years ago, glaciers began to form around the South Pole, which would eventually cover a vast area of the southern Amazon Basin, Southern Africa, Australia and Antarctica. The coldest period was around 293 million years ago. By 285 million years ago, temperatures warmed, and a great deal of the ice retreated, although some glaciers remained. The Permian was cool compared to other time periods, at least until those volcanoes started pouring CO2 (a greenhouse gas) into the atmosphere.

It sounds like the Permian had a lot of diverse climates and ecosystems, right? So as long as we stayed away from that awful desert, we should be able to find a nice place to live. So let's take a look at the neighbors we'd have in the next blog.

 

https://en.wikipedia.org/wiki/Permian

https://en.wikipedia.org/wiki/Emeishan_Traps

https://en.wikipedia.org/wiki/Cimmeria_(continent)

Carboniferous Period

 The Carboniferous Period spanned 358.9 million years ago to 298.9 million years ago. On a time table, it sits behind the Devonian Period and before the Permian Period.

In the Early Carboniferous Period, average global temperatures were approximately 68 F (20 C). During the Middle Carboniferous, they dropped to about 54 F (12 C). Carbon dioxide levels fell during the period from roughly 8 times today's level at the beginning to about the same as today's level at the end. Lack of growth rings of fossilized trees suggest a lack of seasons, or a tropical climate. Glaciations in Gondwana were triggered by its southward movement, and continued beyond this time period.

Also, there was mountain building as continents collided to form Pangaea. There was a minor extinction event at the end of the period, caused by climate change.

Now, the last we heard, pieces of Gondwana had broken off and were sitting at the equator or slightly north, while the rest of Gondwana drifted south to the south pole.

During the Carboniferous Period, the land was covered by vast forests, which would eventually become the coal beds characteristic of this period's stratigraphy. Some of the Early Carboniferous land plants were very similar to those of the Late Devonian, but new groups also appeared. The main plants of the early period were horse-tails, scrambling plants, club mosses, scale trees, and ferns. The club mosses of this period are cousins to today's tiny club-moss, but not ancestors; and they had trunks 30 meters high and up to 1.5 meter in diameter. Another type of large tree was ancestor of today's ferns. These continued throughout the period, but late in the period, they were joined by cycads (a new form of 'seed fern') and plants related to conifers.

At least one tall plant (6 to over 30 meters tall) was related to cycads (often mistaken for palm trees) and conifers and are thought to have lived in swamps. True conifer trees appeared later in the period and preferred higher, drier ground.

During this period, animals and bacteria had great difficulty processing the lignin and cellulose that made up the gigantic trees. After the trees died, they piled up on the ground, occasionally becoming part of long-running wildfires after a lightning strike. Others very slowly degraded into coal. White rot fungus was the first living creature that could process these trees and break them down.

Animal life was well established by now. Amphibians were diverse and common by the middle of the period, the dominant type of land vertebrates. Some were as long as 6 meters, but most were probably about 6 in (15 cm) in length. Some were aquatic and lived in rivers, while others may have been semi-aquatic. One branch of amphibians would eventually evolve into the first solely terrestrial vertebrates. The cooling climate slowed the evolution of amphibians, who could not survive as well in the new conditions.

Insects, spiders, crustaceans, and others were also very common, and many were much larger than those of today. The atmospheric content of oxygen reached its highest level in Earth's history—35% compared to today's 21%—which allowed the land invertebrates to get so large. There was a millipede-like creature that grew to 8.5 ft (2.6 m) long. Startling to come across, but if you could kill it, there should be some meat on all those legs. This was the largest known land invertebrate of all time. Among the insects, there were the griffinflies, which included a dragonfly-like insect with a wingspan of 30 in (75 cm). This was the largest flying insect ever to roam the planet. Many other insects flew and crawled about, including cockroach ancestors.

Reptiles, however, prospered due to specific adaptations, such as the amniote egg, which allowed the laying of eggs in a dry environment. Some of the small lizard-like animals gave rise to many descendants, including reptiles, birds and mammals.

I wanted to include a statement about the marine animals of the time, but that section of the article was mostly full of names and little else. I did gather than sponges were fairly prolific and diverse. Also sharks evolved into a multitude of shapes and sizes. Although sharks were mostly sea creatures, there was one type that would sometimes visit swamps. At least one marine fish explored river outlets, and fresh-water fish were common in rivers.

During the latter half of this period, there were glaciations, which meant low sea levels. The cooling and drying of the climate led to a minor extinction event at the end of the period. The tropical rainforest fragmented and then was devastated by climate change.

 

https://en.wikipedia.org/wiki/Carboniferous

Silurian Period

After the Ordovician Period came the Silurian Period, lasting 24.6 million years, from 443.8 million years ago to 419.8 million years ago. It began approximately the same time as the major series of extinction events mentioned at the end of the Ordovician Period, when a large number of marine fauna were wiped out.

The Silurian saw wide-spread diversification of jawed fish as well as bony fish. Multi-cellular life also appeared on land as small plants similar to liverworts, hornworts, and mosses, which grew besides lakes, streams and coastlines. Invertebrate animals with an exoskeleton also found land during this time period. This includes insects, spiders and crustaceans. However, terrestrial life would not greatly diversify until later.

With the supercontinent Gondwana still covering much of the southern hemisphere, a large ocean occupied most of the northern half of the globe. High sea levels and relatively flat land (there were few significant mountain belts) produced a number of island chains, meaning there was a rich diversity of environmental settings.

What was left of Gondwana remained intact and continued to drift south, but there is evidence that the icecaps were less extensive than those of the late-Ordovician time period. The smaller continents of Avalonia, Baltica, and Laurentia drift together near the equator, starting the formation of a second supercontinent known as Euramerica.

When proto-Europe (Baltica) collided with proto-North America (Laurentia), the collision folded coastal areas from modern New York State through Europe and Greenland to Norway. At the end of the Silurian Period, sea levels dropped again, and the new mountain ranges were rapidly eroded.

The Silurian period enjoyed relatively stable and warm temperatures, in contrast with the extreme glaciations of the period before it, and the extreme heat that would follow it. Sea levels rose during the first half of this period, and fell during the second half.

Climate was warm because high CO₂ levels and warm shallow seas produced a greenhouse phase. Glaciers at the South Pole nearly disappeared entirely. There is strong evidence of a climate dominated by violent storms generated by warm sea surfaces.

The Silurian was the first period to have megafossils in the form of moss-like miniature forests along lakes and streams. The first fossil records of vascular plants (land plants with tissues that carry water and food) appeared in the second half of the Silurian period.

Fish reached considerable diversity. A diverse fauna of sea scorpions (some of them several meters in length) prowled the shallow Silurian seas of North America. Leeches made their appearance.

About the middle of the Silurian, the earliest-known animals fully adapted to terrestrial conditions appeared, including a millipede. There is also some evidence of predatory spiders and millipedes and centipedes. Predatory invertebrates indicate that simple food webs were in place that included prey animals. These may have included those who grazed on micro-organisms.

Yes, we are getting closer and closer modern Earth. That is what happens when you start at the beginning and work your way towards today. I'm still not seeing any fauna that would be worth hunting. Although a millipede several meters in length might have enough meat to make a stew. Is the ground fertile enough to grow carrots and potatoes to put in that stew? And just how bad did those storms get? Maybe I'll keep going before I try to colonize.

 

https://en.wikipedia.org/wiki/Silurian 

Ordovician Period

When I first started reading the article on the Ordovician Period, I got to the mention of Gondwana, which made me stop and wonder, "Wait, haven't we been through this breakup before?" And the answer is yes, we have, in the blog I wrote about the Paleozoic Era, which the Ordovician Period is part of. I had to remind myself that this is not really déjà vue, that the Paleozoic Era has 6 periods to it, and my blog on the Era would have been like an overview, while the blogs on the periods would have more details. So, some of the big events, like the breakup of Gondwana, will be mentioned in both posts.

The Ordovician Period spans 41.6 million years, from the end on the Cambrian Period some 485.4 million years ago to 443.6 million years ago.

Life continued to flourish during the Ordovician Period, although there was an extinction event at the end of the period. The Ordovician Period is known for its biodiversification event, which considerably increased the diversity of life. Invertebrates, namely molluscs and arthropods, dominated the oceans, although fish, the world's first true vertebrates, continued to evolve, and fish with jaws may have first appeared late in the period. Life on land had yet to diversify.

However many meteorites strike the Earth in a year today, there were 100 times that many hitting the Earth per year during this period.

The southern continents were collected into Gondwana, which started the period in equatorial latitudes but then drifted toward the South Pole. Meanwhile, other continents, Laurentia (part of North American), Siberia, and Baltica (northern Europe), were drifting north, and Baltica started moving towards Laurentia later in the period. Another small continent, Avalonia, separated from Gondwana and began moving north towards Baltica and Laurentia.

Temperatures were mild in the early and middle Ordovician Period, but from 460-450 million years ago, volcanoes along one of the oceans spewed massive amounts of carbon dioxide (a greenhouse gas) into the atmosphere, turning the planet into a hothouse. These volcanic island arcs eventually collided with proto-North America and formed the Appalachian Mountains. [At last! I've been waiting for billions of years for the Appalachians to appear!]

Initially, sea levels were high, but as Gondwana moved south, ice accumulated into glaciers and the sea levels dropped. At first, low-lying sea beds increased diversity, but later glaciation led to mass extinctions as the seas drained and continental shelves became dry land. By the end of the period, the volcanic emissions had stopped. By then, Gondwana had neared the South Pole and was largely glaciated.

Reef-forming corals first appeared early in this period. Land plants probably evolved from green algae, first appearing in a form resembling liverworts. Fungi was also an early adopter of living on land, and facilitated the colonization of land by making mineral nutrients available to plant cells.

This period closed with a series of extinction events that are generally regarded as one major event, in which 49% of all fauna died. It is generally agreed that this event or series of events were caused by an ice age. That ice age had several pulses of increasing/decreasing glaciation. Each time the glaciation increased, the sea level dropped, killing many of the fauna that inhabited the shallow seas. When the sea levels rose during the next decrease of glaciation, there were entire families of fauna that had not survived to re-establish themselves in the shallow seas. This may have happened several times, producing a series of extinction events.

Well, now we're starting to get some place. Plants (of sorts) on land, starting to make the soil arable. Not sure about the carbon dioxide level in the atmosphere, but the meteor showers would be beautiful, as long as they didn't land too close. Hunting probably wouldn't do much good yet, but, hey, there's fish! Too bad I can't stand fish.

Maybe the next period will be even more amenable?

 

https://en.wikipedia.org/wiki/Ordovician 

Cambrian Period

 The Cambrian Period was the first geological period of the Paleozoic Era. It lasted 55.6 million years, from 541 million years ago to 485.4 million years ago. The Cambrian is known for sites of exceptional preservation where even 'soft' parts of organisms are preserved, so our understanding of the Cambrian biology surpasses that of some later periods.

A profound change in life on Earth happened during the Cambrian Period, in that mineralized multicellular organisms became common. The rapid diversification of life-forms in this period—known as the Cambrian Explosion—produced the first representatives of all modern animals, probably from a single common ancestor.

Although life prospered in the oceans, the land is thought to have been comparatively barren. Shallow seas flanked several continents and were relatively warm. Polar ice was absent for much of the period.

Large, high-velocity rotational movement of Gondwana appears to have occurred in the early Cambrian, and may have resulted in Laurentia (North America), Baltica and Siberia being 'tossed away' and forming isolated land masses. Most continental land was clustered in the Southern Hemisphere, but was drifting north.

With a lack of sea ice, the sea level was high, which led to large areas of the continents being flooded in warm shallow seas, which were ideal for sea life. The sea levels fluctuated, suggesting there were pulses of expansion and contraction of a south polar ice cap.

The article stated that the Earth was generally cold during the early Cambrian, and then said the average temperatures were 7 degrees Celsius higher than today. That doesn't seem very cold to me.

The Cambrian flora was little different from what had existed in the previous period. Primarily, there were marine macroalgae in the seas, and that was pretty much it. There were no land plants known from the Cambrian, although biofilms and microbial mats were well developed on tidal flats and beaches 500 million years ago. There were also microbes forming microbial Earth ecosystems, comparable with modern soil crust of desserts, which contributed to soil formation.

It was once thought that trilobites were the dominant life form of the time period. But it turns out that these had a heavy armor which fossilized far more easily than the bodies of other animals, so there were plenty of trilobite fossils, even though trilobites were only a minor part of the animal diversity.

Earth suffered a mass extinction at the start of the Cambrian Period. It is thought that animals that burrowed into the sea bed, destroyed the microbial mats covering the seabed, and many organisms dependent on the mats became extinct, while other species adapted to the changed environment.

Despite the 'Explosion' at the start of this period, the later half saw a sharp drop in biodiversity. 500 million years ago, oxygen levels in the oceans dropped dramatically, while the level of poisonous hydrogen sulfide increased, producing more extinction events, making the latter half of the period surprisingly barren.

However, some organisms did venture onto land, producing trace fossils of their movements. Some of these fossil trackways suggest a large, slug-like mollusc.

Just when you thought Earth pre-history was going to get interesting, it takes one step forward and two steps back. Dry land is still pretty barren, except for an occasional slug-mollusc looking for some tasty soil microbes.

Well, we're pretty sure humans arrive on the scene eventually, so we're just going to keep slogging forward until we find us.

 

https://en.wikipedia.org/wiki/Cambrian

Paleozoic Era

 The Paleozoic Era is the earliest era of the Phanerozoic Eon. It is the longest of the Pahnerozoic eras, lasting from 541 to 251.902 million years ago. (I am left wondering why such an odd date for an ending? Why not 252 million years ago? I hope they offer an explanation.)

The Paleozoic was a dramatic time, incorporating geological, climatic and evolutionary changes. There was an explosion of variety in lifeforms, in which almost all modern families appeared. This began in the ocean, but eventually transitioned onto land. Great forests of primitive plants covered the continents, and towards the end of the Paleozoic, the first modern plants (conifers) appeared.

The Paleozoic Era also saw the largest extinction event in the history of Earth. This catastrophe was so devastating that it took life on land 30 million years into the next era to recover. Life in the sea may have recovered much faster.

During the early part of this era, the climate was probably moderate, becoming warmer as the second-greatest sea level rise of the era occurred, where the sea level was 200 meters above today's levels. Gondwana moved south until West Gondwana (Africa and South America) lay directly over the South Pole, while most of the parts that now reside in the northern hemisphere remained in the tropical zone, and China and Australia lay in a temperate zone. This warm period ended rather abruptly with a short but severe ice age that caused the second-greatest mass extinction of the Phanerozoic time. This ice age was only 30 million years long, and occurred 445 million years ago.

Sea levels dropped, of course, during the ice age, but slowly recovered over the middle of the Paleozoic. Bits and pieces of Gondwana moved northward, which created numerous new regions of warm, shallow sea floor. As plants took hold on the continental edges, oxygen level increased and carbon dioxide dropped. The far southern parts of Antarctica and West Gondwana became less barren.

Then a spike in atmospheric oxygen (while carbon dioxide plummeted) destabilized the climate and led to one or perhaps two ice ages. These were even more severe than the brief one already mentioned, but the effects on the world biota were mostly inconsequential. The oxygen and carbon dioxide level returned to more normal levels, but the assembly of Pangaea created huge inland areas that were subject to temperature extremes. The end of the era saw a huge mass extinction event.

While macroscopic plant life possibly appeared before this era began, plants mostly remained aquatic until about 420 million years ago, when they began to explore dry land. They reached a point where towering lycopsid (a type of plant that includes clubmosses, firmosses and quillworts) rainforests dominated the tropical belt of Euramerica. Climate change caused this rainforest to collapse, fragmenting this habitat and diminishing the diversity of plant life.

Nearly all of the invertebrate animal phyla appeared in great abundance at the beginning of this era. The first vertebrates were primitive fish, which lost no time in diversifying. Some fish had lung and powerful bony fins that allowed them to crawl onto land about 367.5 million years ago. Their fins evolved into legs about 390 million years ago. Amphibians were dominant for a time, until the climate change that reduced the rainforests also greatly reduced the amphibian diversity. Then reptiles prospered and increased in number and variety by the end of the era.

I'm sure we'll get even more details when we study each period of this era.

 

https://en.wikipedia.org/wiki/Paleozoic

Ur...

Okay, not a lot of information on this subject. Only to be expected, I suppose, since Ur is the name given to the very first super continent, which came into being about 3.1 billion years ago. At that time, the only life on Earth was single-celled, and some of it knew how to photosynthesize. And it’s called a super continent, though it was probably smaller than modern Australia.

It qualifies as a super continent because it incorporated all or nearly all pieces of land then in existence. More recently, scientists have started calling Ur and other small ‘super’ continents by the term super-cratons. The best I can figure is that a craton is a piece of land considered too small to be a continent.

Other scientists have postulated the existence of another super-craton at about the same time, which they have called Vaalbara, but apparently, the ideas of these two early cratonic assemblages are incompatible.

About 1,300–1,071 million years ago, Ur joined the continents Nena and Atlantica to form the supercontinent Rodinia. In one proposal, Ur remained the nucleus of East Gondwana until that supercontinent broke up. But in other proposals, India and East Antarctica did not collide until Rodinia formed 1,071 Million years ago. However, during that time period, the Earth’s mantle was 200 degrees C hotter than today, making many characteristics of modern tectonics rare or non-existent. This would preclude Roger’s 3 billion years ago supercontinent of Ur.

The proposal for the super-craton Vaalbara places two cratons, Kaapvall of southern Africa and Pilbara of western Australia, next to each other based on stratigraphic similarities. In Roger’s configuration of Ur, these two cratons were placed far apart during Gondwana, which is contradicted by widespread collisional events between Australia and Africa.

Yet another possible supercraton, Zimgarn, was proposed by Smirnov in 2013. Unfortunately, I didn’t understand the paragraph dealing with it, so I’m mostly ignoring it. After all, I’m supposed to be studying Ur.

Geological similarities in parts of India (Singhbhum and Dharwar), western Australia (Kilbaran and Pilbara), and southern Africa (Kaapvall and Zimbabwe) indicate these area were close together in the Mid-Archaean Era. Ur was named for the german prefix meaning “original” by Rogers because in his proposal, it was the first continent. Other Archaean continental assemblages are considerably younger. In some reconstructions, the various pieces of Ur stayed near each other until the break-up of Gondwana.

So, was there really an Ur, as proposed by Rogers? Should it really be called Vaalbara or Zimgarn? Or something else entirely? I didn’t find any indication of where it was located, and given how long it supposedly existed, it could have drifted quite a ways from its original location, but still, I would have liked to see some of that type of information.

How many planets do you suppose are out there with only single-celled life and 1 large island? With such a small land mass, would it be worth it to colonize it?

 

https://en.wikipedia.org/wiki/Ur_(continent)

https://simple.wikipedia.org/wiki/Ur_(supercontinent)

Dinosaurs

Like most kids, I had a steady interest in dinosaurs when I was young. I never truly outgrew that interest, and the science magazines I read don’t have much to report on them very often. How disappointing. I long to learn all the new stuff they’ve learned since I was a kid. Can you imagine my surprise a few decades ago when I discovered Fred Flintstone’s powerhouse Brontosaurus never actually existed? It was the result of a few bones that did not necessarily belong together and a scientist’s active imagination while trying to put them together.

One of my school science projects was on dinosaurs. I bought several giant bars of Ivory soap and tried to carve them into various dinosaurs. The T-Rex didn’t want to stand up, the stegasaurus’ back plates were difficult to carve without breaking them off. The easiest to carve was the brontosaurus, which way back then still had a place on the dinosaur family tree.

I can’t do justice to dinosaurs in a few hundred words. After all, they were around - in one form or another - for millions of years. So I plan to look around, pick some interesting versions and report on them over the course of several months.

What do you think you know about dinosaurs? Were they all cold-blooded? Covered in reptile scales or simply skin similar to our own? Did they do any parenting of their young, or simply lay their eggs and move on through the countryside? Did they really evolve into birds? How big did they get? What was their smallest representative? Are there any ‘dinosaurs’ alive today, or maybe animals that look very similar to their ancient ancestors?

I remember a story - I don’t remember if I saw it visually or read it - where a group of hadrosaurs (That’s what I remember their type being, but I may be completely wrong.) had left Earth in some fashion back in the Long Ago, and established a home on another planet in another system. And now their descendants were space travelers and meeting humans in the vastness of space.

Wouldn’t that be something?

Well, since we’re approaching that point where we may be space traveling in a few generations (meaning, outside our home system), maybe we should be considering what evolved dinosaurs might be like. And to do that, we should start by learning what dinosaurs were actually like.

Any suggestions you want me to look at?

Everybody’s Heard of Gondwana

Gondwana existed from about 550 million years ago until 180 million years ago. It is one of the most well known super-continents, in the sense that more people have at least heard of it, rather than individual cratons like Avalonia or Baltica.

If I’m reading the information correctly, Gondwana existed both before and after Pangaea. Before Pangaea, it came into being when several cratons stuck together, beginning about 800 million years ago with the formation of the East African Orogeny, which involved the collision of India and Madagascar with East Africa. Between 600 to 530 million years ago, this group added South America, Australia and Antarctica, in that order. Thus Gondwana was born.

Eventually, it merged with Laurasia and became Pangaea, sometime around 335 million years ago. But it wasn’t an easy relationship, you might say. Pieces of what had formerly been Gondwana kept breaking off, drifting north to join the former Laurasia section, such as bits of China and Indo-China. The western edge of Pangaea was beginning to break up while the eastern edge was trying to collect itself together.

Meanwhile, the formation of Pangaea and its mountains greatly impacted sea levels and global climate, producing glaciers and continent-wide sedimentation.

But what about Gondwana? About 175 million years ago, it had had enough and broke away. But it didn’t come out of it unscathed. Besides the bits that had already drifted to ‘the other side’, Florida, southern Georgia and Alabama stayed attached to North America.

Once it separated from its partner, Gondwana just kept falling apart. About 132 million years ago, Antarctica, Australia, India and Madagascar broke off and then broke up, going their separate ways. South America slowly broke away from Africa, starting in the south and going north, but the exact timing is uncertain. It could have started as early as 190 million years, and finally finished around 85 million years ago.

So, if you’ve been paying attention, you’ll realize that most of the cratons that formed Gondwana now inhabit the southern hemisphere. Its remnants account for about 2/3 of today’s continental area, including Africa, Antarctica, Arabia, Australia, Indian Subcontinent and South America.

If I were a paleo-geologist, I might have made more sense out of the wiki articles I consulted on this subject. The writer of these articles - particularly the one on Gondwana - seemed to think that anybody who was looking up this subject must be a student, for he/she/it kept using names and terms that I - as a lay person - did not know, leading to much confusion on my part. It seemed far more detailed than I felt I could fit into a blog, anyway, so I skipped lightly through most of it, looking for the important details without bogging down the blog.

Paleo-geology was going to be an elective of mine in college, but I didn’t get that far. Hmm, anybody got a good used textbook on the subject?

https://en.wikipedia.org/wiki/Gondwana

https://en.wikipedia.org/wiki/Pangaea

A Brief Study of Euramerica

Sometimes it’s called Euramerica, sometimes it’s known as Laurussia (not to be confused with Laurasia). It’s called a minor supercontinent because it consisted of several (3) cratons, which are pieces of crust that include land.

About 410 million years ago, the Laurentian (most of North America), the Baltica (Baltic states) and Avalonia cratons all slammed together to form Euramerica. Avalonia was the smallest of the 3; a microcontinent that was long and skinny and sat along the southern border. Euramerica appears to have sat pretty squarely on the equator and was mostly covered with tropical rainforests.

Around 300 million years ago, the climate changed rather abruptly. Many of the lycopsids - such as clubmosses - were replaced by ferns. There was a great loss of diversity in amphibians while the reptiles diversified.

Later, Euramerica became part of the major supercontinent Pangaea. When Pangaea broke into two continents - Gondwana and Laurasia - Euramerica was a part of Laurasia.

Eventually, Laurasia split into the continents of North America and Eurasia. The Laurentian craton became a big portion of North America. Baltica became part of Eurasia. Avalonia ceased to be a long skinny microcontinent as bits of it became some of the east coast of North America, and bits became parts of Ireland, England and other areas of southern Europe.

https://en.wikipedia.org/wiki/Euramerica

https://en.wikipedia.org/wiki/Avalonia

Baltica

Despite my confusion over the location of ‘the Baltic States’, they are right where normal people would expect them; along the Baltic Sea. Somehow, over the years, my mind had decided that the otherwise-un-named Baltic states were located immediately north and northwest of Greece. However, I looked them up (for the sake of this blog), and boy, was I wrong. I had put these states in Eastern Europe, but way too far south.

The Baltic States (Estonia, Latvia, and Lithuania) are in Eastern Europe, snuggled up east of the Baltic Sea and west of the Ural Mountains of Asia. And that places them right on the protocontinent of Baltica!

So, yes, this is kind of related to the Supercontinents blogs, but I’m only going to explore this one little piece of crust. Sometimes it roamed around on its own. At other times, it gathered together with other pieces of crust. Right now, it is smooshed between NorthEastern Europe and NorthWestern Asia. Will it succumb and eventually be pushed under these larger plates, or will it somehow break free again? I don’t know. But let’s see what is known about it.

The thick core of Baltica is also known as the East European Craton and is more than 3 billion years old.

About 2 billion years ago, small pieces of crust started colliding. These included Sarmatia (which was the Ukrainian Shield and Voronezh Massif*) and Volgo-Uralia. That seemed to work pretty well, so about 1.8 billion years ago, they added Fennoscandia, which included the Baltic Shield.

Now, if I’m reading the articles right, about 750 million years ago, Baltica and Laurentia (most of North America) both rotated clockwise, bumped each other lightly and headed for the south pole. At some point (possibly 650 million years ago), it is postulated that Earth became completely covered in snow and ice. (Yes, Snowball Earth.)

It turns out that Siberia was located fairly close to the South Pole, too, and it apparently didn’t take long for Siberia to completely lose its cool. According to one theory, Siberia started having some severe volcanic eruptions, and the build-up of green house gases in the atmosphere from that source resulted in a complete melt-down of all that snow and ice in as little as 2,000 years.

Anyway, Laurentia beat feet and headed north, but Baltica remained in the south at least long enough to hang around Gondwanaland. After that, Baltica drifted north and approached Laurentia again. However, around 425 million years ago, Scotland-Greenland and Norway all collided together, forcing Baltica to look elsewhere for new continental buddies.

Just when you thought you’d found a friend. Poor Baltica.

* Now a piece of Central Russia

https://en.wikipedia.org/wiki/Baltica

https://www.google.com/search?q=baltic+states&oq=Baltic+states&aqs=chrome.0.0l6.4638j1j7&sourceid=chrome&ie=UTF-8

Cambrian Period

The Cambrian Period lasted from 541 to 485 million years ago. At the beginning of this time period, the small unicellulars that represented most life on Earth became more complex and multicellular. They also diversified quite rapidly, bringing forth the first representatives of all modern animal phyla. Indeed, there is strong evidence that all animals evolved from a single common ancestor.

Life prospered in the oceans, but the land is thought to have been relatively barren, with nothing more complex than a microbial soil crust or biofilm. A few molluscs may have emerged to browse on that biofilm, but the continents were probably dry and rocky. The global supercontinent Pannotia had just broken up during the early part of the period, and the new continents were mostly flanked by shallow seas, which were relatively warm. Polar ice was absent for much of this period.

Most land masses were clustered in the Southern Hemisphere during this period, but were drifting north. During the early portion of the Cambrian, the supercontinent of Gondwana went through some large, high-velocity rotational movements.

Trilobites (I wrote about them in an earlier post) were rampant during the Cambrian period. Possibly this was because without any sea ice, the sea level was high, which meant large areas of the continents were flooded in warm shallow seas, which is ideal for sea live. But the sea levels did fluctuate somewhat, suggesting there were ‘ice ages’, possibly meaning pulses of expansion and contraction of a south polar ice cap. Although the beginning of the period was cold, the average temperature during the Cambrian was 7° Celsius warmer than today.

Even so, trilobites were not the dominant species, as was once thought. It seemed they were, because they had hard external shells that were easy to fossilize, much easier than the thin chitinous shells of other arthropods, and so trilobite fossils were much easier to find by today’s paleontologists.

The Cambrian period is often referred to as ‘the Cambrian Explosion’, indicating a huge increase in the variety and diversity of life forms. But it seems (to me) that it might be better to think of it as ‘the Period of Great Changes’. At the start of the Cambrian, new creatures with new behaviors and lifestyles destroyed the biofilm that covered the sea floor, so all the creatures (from the previous time period) who depended on that biofilm died out.

Around 515 million years ago, the number of species dying out was larger than the number of new species coming into existence. 500 million years ago, the oceans saw a big drop in the oxygen content, and at the same time, the level of toxic hydrogen sulfide increased. Either of these events alone could produce extinctions, so imagine what happened when they came in together.

Where would hydrogen sulfide have come from? There are a few ways nature makes it, including anerobic digestion by certain biofilms in the absence of oxygen. I can’t rule that one out, but I’m somewhat more inclined to ‘blame’ volcanoes, which also produce it, probably in larger quantities and certainly can do it in oceans. Also, the heat given off by the volcano(es) would tend to drive oxygen out of the water. So, was there a series of huge volcano events 500 million years ago? I don’t know. It seems possible.

And there we have the Cambrian period in a nutshell. No fascinating dinosaurs to study, but the thought of a spinning Gondwana certainly has my attention.

https://en.wikipedia.org/wiki/Cambrian

https://en.wikipedia.org/wiki/Hydrogen_sulfide