Era, A large chunk of time with an Eon. Eras usually end when a major event happens, Eon, The longest division of time, Precambrian, The earliest and longest stretch of Earth's history, species, A specific group of living things that are similar enough to breed and have offspring together , Index fossil, A specific fossil used to identify the age of a rock layer, Fossil, The preserved remains or traces of a living thing from a long time ago, vertebrate, an animal WITH a backbone , invertebrate, an animal WITHOUT a backbone, cyanobacteria, Tiny, blue-green bacteria that were some of the first life forms on Earth. They created oxygen!, natural selection, Animals with the best traits for their environment stay alive and have babies, passing those traits on, organic evolution, The process of how species change over very long periods of time to survive better, trilobite, A hard-shelled sea creature that lived millions of years ago. They are extinct now but help scientists date rocks, Epoch, A smaller piece of time within a period (it is inside an Era), Period, A unit of time that is smaller than an era but larger than an epoch.

Geologic Time

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