Good afternoon, everybody! Today, I think it's time to talk about the time when jaws emerged and the seas were sporadic - the Silurian period!
I was going to have a picture here, but… it was deleted on Wednesday.
Four hundred and forty-three million years ago is when today's story begins. Oxygen levels were only 70% of what they are today. On the other hand, carbon dioxide levels were eleven times higher than what they are today, so…The period itself began with the second-largest of the five major extinctions in Earth's history - 60% of all marine species became extinct. The main supercontinent - Gondwana - edged itself upwards through the southern hemisphere throughout the period while Earth as a whole saw the temperature soar thanks to the high levels of CO2.
Land animals were only just beginning to get a foothold on Earth at this point - but the oceans were full of them! The Silurian was when bony fish first appeared; bones were soon followed by jaws. (And with jaws came sharks!)
Plants were starting to climb up onto land as well - the long-extinct genus Cooksonia includes the oldest-known plant to have vascular tissue (xylem and phloem.)
In conclusion, then, the Silurian was a period mostly consisting of ups and containing two incredibly important developments (jaws and vascular tissue) that would prove hugely important in the future.
Anyway, that's all I have for this week. I'm sorry about not posting last week. I did intend to have this done for last Sunday. Then I looked at the time… it was about 2pm.
Either way, I'll see you next week - so stay safe until then!