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

Phanerozoic Eon

 The current geologic eon of Earth is the Phanerozoic Eon. It started 541 million years ago and continues today. It is the only eon during which abundant animal and plant life has existed. It began at about the same time that animals first developed hard shells, as preserved in the fossil record.

During the early stages of the Phanerozoic Eon, a number of animal types came into existence and evolved into diverse forms, and complex plants emerged and developed. In addition, fish, insects and tetrapods (which includes all living and extinct species of amphibians, reptiles, birds and mammals) also emerged and evolved. Plant life appeared on land early in the eon.

Pangaea was the most recent supercontinent during the early days of this eon, but tectonic forces broke it up into the current continental landmasses, and then proceeded to move them around into their current configuration.

The Phanerozoic Eon consists of 3 eras, which are broken up into 12 periods. Now that plants and animals have shown up in earnest, I expect there will be plenty of information about what was going on during each segment.

In fact, the article I found for this eon actually had paragraphs (or more) for each period, but I skipped over them because I didn't want to get ahead of myself. I hope I remember to check back to this article if I have trouble finding information on the eras and periods that comprise this eon.

This is a very short blog, not because I couldn't find much information, but because there was so much information, it needs to be broken into smaller time segments to get that information into manageable bites. But do stay tuned, because we are finally approaching Dinosaur Land!

 

https://en.wikipedia.org/wiki/Phanerozoic#:~:text=The%20Phanerozoic%20Eon%20is%20the,preserved%20in%20the%20fossil%20record.

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