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Sprawling moss, towering trees, flying insects, limbed amphibians: Early species vied for domination as the land went from hostile to hospitable.
For billions of years, land on Earth was uninhabitable. But in the seas, predation allowed species to thrive before — and after — two mass extinctions.
After Earth's third mass extinction, mammals' surviving ancestors ruled the supercontinent Pangea. But lizards soon ushered in the age of reptiles.