Evolution

During the "lock down" of 2020, one of my goals was to come up to speed on evolution.

I feel really, really good how far I've come.

The earth has four named EONs: the Hadean, the Archaean, the first animal eon (the Proterozoic eon), and the visible life eon (Phanterozoic).

The Cambrian was the first period of the first era, Paleozoic, of the visible life eon (the Phanterozoic). This was the the biggie, the Cambrian. All modern life forms were developed in the Cambrian.

Paleontologists have tried to find evidence of "first life" in the Proterozoic Eon. The last period of the Proterozoic Eon was the Ediacara Period -- and this is where, as it stands now, where evidence of animal life was first found: the Ediacaran fauna. It appears that the first animal split into two major divisions:
sponges: no consistent body form
jelly fish and comb jellies: biradial body form introduced and which all modern animals, other than sponges, have
one wrench in the gear box: placozoans. They may be a completely separate branch from sponges and eumetazoa (true animals); Dickinsonia may be a placozoan. There may be three recognized genera and three species of placozoans.

The Cambrian exploded with life. But three mass extinctions, in or at the end of the Paleozoic era almost ended everything: the Ordovician-Silurian mass extinction was the first; then the Devonian (apparently somewhat unremarkable, or little known about it) and then the biggie of the three, the mass extinction at the end of the Permian. Trilobites were finally done in by this mass extinction and thus the trilobites never "saw" the dinosaurs. If one finds a trilobite fossil, one knows one is in the Paleozoic era. The oldest coelocanths and the first amphibians appeared at the same geologic time.

The amphibians had their fifteen minutes of fame: critical transition from sea to land, but only three surviving groups: frogs; salamanders (and newts); and, caecilian worms.

The reptiles appeared next, and though most people think this is a big group, it really is not. The modern reptiles are pretty much reduced to turtles, tuaturas (in New Zealand only), lizards, and crocs/alligators. Not very impressive in the big scheme of things, but they figured out the "egg."

The Mesozoic era is the era of dinosaurs: Triassic, Jurassic, and Cretaceous. A fourth major mass extinction occurred at the end of the Triassic which was also a biggie, knocking off a lot of dinosaurs, but they survived until the fifth and last major Phanterozoic eon mass extinction, the most famous of all, the Cretaceous-Paleogene (K-Pg) extinction.

Everyone knows the "K-Pg story" that allowed the inconsequential mammals to succeed. Within the past few years, the concept of "mammal-like reptiles" has started to disappear. The "mammal-like reptiles" were either mammals in their own right, or something between reptiles and mammals, but definitely not reptiles. The best example of the latter is the dimetrodon, extinct genus of non-mammalian synapsids. The dimetrodon is often portrayed with the dinosaurs but it is not a dinosaur. It's a synapsid is more akin to a mammal than a dinosaur.

The Mesozoic era had three periods, as mentioned above. The Mesozoic was followed by the Cenozoic ("ceno" - Greek for new, fresh, recent) -- "fresh life" -- the mammals. The Cenozoic used to be called the Tertiary. The Cenozoic has only two named periods, the Paleogene and the Neogene (no "mesogene") but there is a "transition term / jargon": quaternary -- sort of a combination era/period.

We reside in the Holocene epoch, preceded by the Pleistocene epoch, beginning 2.6 mya and extending to 11,700 years ago.

And that's the two-minute synopis.

I'm trying to get it to a 30-second elevator speech but it's a bit difficult.