Roughly 4 billion years ago life on our planet started to form, they were small one-celled organisms similar to bacteria. Millions of years later after the Archean Era came to a close we see more developed life forms appear in the Proterozoic Era. Algae, jellyfish, and actual bacteria started to appear 2.5 billion years ago. It took a long time for life to pick up after that.
550 million years ago we enter the Paleozoic era and the Cambrian period emerges. The Cambrian period is the mark of when the first invertebrates evolved, brachiopods and trilobites, a family line that has long been extinct. After that is the start of bony fish such as Leedsichthys, in the Ordovician period 500 million years ago. 50 million years later, the bony fish began to walk onto land. The Silurian period brings amphibian-like species and the first land animals. Roughly 400 million years ago, for the fish still in the water (in the Devonian period) they became lighter and developed cartilage; alongside them are the first seedless plants. The Carboniferous period brings many crionoids-plants into the world and dawns the rule of the insects. It lasted for roughly 50 million years. Finally in the Paleozoic era it ends with the dawn of reptiles, the Permian period. At the end of the Permian period there was a mass extinction killing about 80% of life.
But the end dawned a new age, the age of the dinosaurs. In the Mesozoic era there are three periods: the Triassic, Jurassic, and Cretaceous. The Triassic period starts around 250 million years ago- life had to not start over but start from basic versions of what the dinosaurs will become. The Jurassic period is next holding the rise of the dinosaurs- the large dinosaurs started to appear. The Cretaceous period is the most notable and holds many of the dinosaurs we recognize today such as the T-Rex and the Tricaratops. Sadly, the reign of the dinosaurs ended with an asteroid that killed 90% of the population roughly 65 million years ago.
This dawns the age of the mammals, the Cenozoic era starts with the Paleocene period. This period is mainly recovering from the asteroid that killed the dinosaurs, however at the end many large herbivorous mammals start to appear as well as early ancestors to the carnivorous predators in the mammalian family today. Next, in the Cenozoic era is the Neogene period where the mammals we know from the ice age appear. The woolly rhino and woolly mammoth are great examples and when ancestors of Homo sapiens, us, showed up. This period ended around 2 million years ago and sprouted the Quaternary period, which is ongoing and when people started to evolve.
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