Geologic Time 1

(Answer on a Lecture Note Page) What Happened First? (Answer on a Lecture Note Page) 2

Preserved remains of ancient life Fossil Preserved remains of ancient life Found mostly in sedimentary rock Never in igneous rock 3

Body is covered by sediment (quickly...days) Formed (usually) An organism dies Body is covered by sediment (quickly...days) Slowly hardens into a fossil Fleshy parts decay Hard parts leave fossils 4

Molds & casts Mold is hollow area left after organism finally decays Example 1: Molds & casts Mold is hollow area left after organism finally decays Cast is when mineral deposits fill the mold, creating a copy 5

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Example 2: Carbon Film Thin coating of carbon left behind on a rock 7

Trace Fossils Show evidence of activity Not the organism itself Example 3: Trace Fossils Show evidence of activity Not the organism itself Footprints burrows 8

Provide evidence of how life has changed over time Fossil record Provide evidence of how life has changed over time Older fossils (found deeper) have simplest structure. Give clues to past environments 9

Supports the theory of evolution Remains of many extinct species 10

Relative age Finding age of rocks Absolute age Older or younger than other rocks Absolute age How old it is since formation 11

Look at rock layers Relative age Those on bottom formed first Each layer on top is newer than the one below it “Law of Superposition” “Law of Original Horizontality” Layers get deposited “flat” 12

Look at Faults Crack in the Earth’s surface Layers do not line up anymore Fault is younger than the rock it splits 13

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Look at Igneous rock layers Extrusion – layer of lava Younger than rock below it Intrusion – pocket of magma pushed into other rocks layers Younger than rock below & around it 15

Unconformity – gap in the geologic time record Missing part of the rock from erosion 16

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Use index fossils Certain fossils occur all over For short period of time Example: trilobites Find index fossil tell relative ages of rock layers for different areas of the world 18

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Geologic Sequence Example