fossils

the remains of animals or plants, footprints and burrows found in sedimentary rocks. animal either eaten or decomposes

different form of life that existed on earth also major changed in earths history

rare event, small chance of being preserved, some organisme have better chances bc: composition of skeletons or where they lived

internal organs, skin, hair, muscles etc..

analyze the layers or strata that build over time, layers are formed by sedimentary rocks, younger layers are on top or older layers.

oldest layer is at the bottom and youngest at the top

comparing locations of fossils, does not give exact age but shows the order based on the stratigraphic layers

shows the age of the fossil, counting tree rings

uses radioactive isotope of carbon to determine how it decays over time

precambian, paleozoic, mesozoic, cenozoic

-formation of earth -first sign life -bacteria -oxygen in atmosphere -first aquatic soft-bodied organisms

4 billion yrs

-aquatic invertabrates w hard shell - large extinction of aquatic life -plants, amphibians on dry land -trees, reptiles -largest mass extinction caused by glaciation

300 million yrs

-warm climate, more large reptile -extinction killing 50% of marine life -first birds and small mammals -dinosaurs -extinction causing dinosaur disappear

-long cooling and drought period -large mammals -primates and hominids -present