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