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The evolutionary sequence of life on Earth
Transcript of The evolutionary sequence of life on Earth
Setting the Stage
Early Earth, 4.6 billion years ago, was not a very nice place; volcanic, bombarded by cosmic radiation, no water, constantly hit by meteors.
In order for the first life to form...
1. volcanic OUT-GASSING added gasses to make the protective atmosphere
2. Meteors carrying water from space built up the OCEANS
3. Sometime around here, the first life-forms developed
4. Single-celled organisms in the oceans produced OXYGEN by photosynthesis, leading to huge deposits of iron ore (Banded Iron Formations).
Multicellular life in the oceans
550 million years ago simple life forms evolved and became more complex life forms.
The oceans were full of small soft-body creatures (no bones, no shells)
ocean creatures with shells
542 million years ago, ocean creatures evolved to include organisms with shells.
mass extinction kills almost all ocean creatures
After the Cambrian extinction new organisms evolve, including the first fish and coral reefs, about 450 million years ago.
First life forms on land
420 million years ago the first land plants (mosses and lichens) form on land and insects evolve.
life on land diversifies
410 million years ago forests grow on the land and the first sharks evolve.
devonian mass extinction of marine animals
360 million years ago many ocean creatures went extinct again! This lead to the evolution of the first amphibians, reptiles, and seed plants on earth.
Age of dinosaurs
Following the Permian-Triassic extinction 251 million years ago giant reptiles existed in every part of Earth. The earliest mammals evolved, they were small rodents. The earliest birds evolved from dinosaurs and the first flowering plants evolved as well.
Age of Mammals
65.5 million years ago the last extinction event occurred and killed all of the dinosaurs. This allowed the mammals to become the most dominant animals on Earth.