history lesson 1 (arthropod and nonarthropod, cambrian period) (from what i've learned from not quite trustworthy sources) and my stuff

Credits to: 

'The Cambrian Period (That We Know Of) ft. Animalogic' by Linsday Nikole on YouTube

'Prehistoric Bug Extravaganza' by The Budget Museum on YouTube

What Came Before the Cambrian Explosion?

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The Cambrian period (542 - 488 m.y.a.) is part of the Paleozoic Era. It started with a variety of animals appearing in the world, most of these animals evolving into major groups over time. It's difficult to differentiate in this time what is and what isn't part of the arthropod family, so for this I will be speaking about any animal in the Cambrian Period.

In the Cambrian Period, the climate was generally warmer due to the lack of land and plants. There was a decent amount of oxygen on Earth, compared to before the explosion of life occurred. The oceans were scattered in mass amounts of nutrients, newer evidence supporting the idea of bursts of oxygen cycling through the water, helping the new living beings adapt to their environment. Despite all this, no scientist is sure what exactly caused this period.

There were animals alive previously before the period, but they were more restricted in their diversity. Throughout some million years, even newer animals showed up that broke the line between the Cambrian and the Ediacaran periods, according to their new morphologies, behavior, and diets. Some Ediacaran animals played a big part in creating the ecosystem in the Cambrian, an example being a Precambrian animal shown burrowing in fossil records while also helping Cambrian predatory animals take form to eat. A common response to predatory relationships by the prey was biomineralization, which involved calcium in order to provide the shells for these animals.

The main major groups appearing in the Cambrian included Arthropods, Mollusks, Annelids, Echinoderms, and Chordates. Some vertebrates and Primates, including humans, belong to Chordates. All Chordates have a notochord, a dorsal hollow nerve cord, pharyngeal gill slits, and a post-anal tail. 

(REST IS WORK IN PROGRESS WILL RESUME WHEN NO LONGER BURNT OUT LOL!)