Precambrian Era: Earth approx. 4.6 billion years: oldest evidence of life (prokaryotic) between 3.5 & 4 billion years ago, cyanobacteria and the start of photosynthesis >2.5 billion years ago, first evidence of eukaryotic cells about 1.5 billiln years ago, first multicellular life forms (ex. sponges & jellyfish) approx. 700 million years ago, Paleozoic Era: Cambrian explosion of invertebrate life: approx. 545 million years ago, first vertebrates (fish): approx. 500 million years ago, first land plants: approx. 450 million years ago, first land animals (insects and amphibians): approx. 400 million years ago, first reptiles: approx. 300 million years ago, Mesozoic Era: first dinosaurs and mammals: approx. 225 million years ago, first birds: approx. 150 million years ago, dinosaur extinction: approx. 65 million years ago, Cenozoic Era: mammals dominate major land niches (whole era), first hominid: approx. 7 million years ago, Homo sapiens: approx. 200,000 years ago,

Geologic Time Scale: Major Events

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