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Geologic Time Scale & Fossils Notes Part 1 Rock Types & Fossils •There are 3 types of rock: –Igneous, Sedimentary, and Metamorphic –Sedimentary rocks often contain fossils •Organic sedimentary rocks: “Once-living organisms” = fossils Rock Layers •The earth has distinct layers of rock –The rock layers show a progression of organisms from layer to layer –The oldest layer is on the bottom, then each layer up is younger, with the youngest layer being on the top •This is because sediment is deposited on top of previously existing sediment. Relative Dating •Relative dating can be used to estimate the order of prehistoric and geologic events •This happens by observing where fossils are found in layers of rock –The oldest rock layers contain the oldest fossils and the youngest rock layers contain the youngest fossils –A fossil must have existed at the time when the rock layer was formed, which is how we can tell Relative Dating Timelines & Earth’s Age •Timelines describe the timing and relationship between events in the Earth’s history. •Earth is estimated to be 4.5 billion years old (byo). Fossils •A fossil is an imprint, replacement, or remains of an organism from ancient times. • •Fossils provide… –a historical perspective on change of the Earth. –a biological record of life on Earth. –a record of how organisms have changed over time. Fossil Record • The fossil record can be aligned to the major environmental changes that have occurred on Earth. •The fossil record provides evidence from a “living laboratory.” •The fossil record illustrates how organisms responded to environmental change. –Some fossils provide a continuous record of environmental change.