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Eras and Fossils

QuestionAnswer
Eras Major subdivisions based on differences in life forms.
Precambrian Longest era. Bacteria formed O₂, Ozone (O₃) began to develop, and the atmosphere began to form.
Paleozoic Age of Fish. Appalachian Mountains formed. First trilobites (small, shelled sea creature resembling a modern crab).Became the first dominant form of complex life on earth.
Mesozoic Age of Reptiles. Started with the rise of the dinosaurs. The end of the Mesozoic was marked by the extinction of the dinosaurs.
Cenozoic Age of Mammals. Many mountain ranges formed - Alps in Europe, Himalayas in India, Rockies' in the US.
Extinction of dinosaurs Leading theory for dinosaur extinction: asteroid hit. A layer of iridium (found in meteorites) can be found across the globe in rock layers around 65 million years ago.
Fossil The remains, impressions, or other evidence of the former existence of life preserved in a rock.
Mold A cavity left by an organism where the ground hardened before the organism had decayed.
Casts Where the cavity left by an organism has been filled, usually by minerals.
Original remains (preserved) Are when the actual remnants of an organism are discovered. This may be in the form of a bone or tooth or shell, in frozen remains (like a wooly mammoth) or an insect in amber.
Trace fossils Are not the actual organism but rather the evidence that an organism once existed.
Index fossils Fossils that lived in a wide geographic area, lived a short time and is easily recognizable.
Created by: jadams2021
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