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Fossils. Ch. 13 Section1 . Fossils. Remains , imprints , or traces of prehistoric organisms Scientists who study fossils are paleontologists . Fossils tell us when , where , and how organisms lived. Most Fossils are found in sedimentary rocks.
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Fossils Ch. 13 Section1
Fossils • Remains, imprints, or traces of prehistoric organisms • Scientists who study fossils are paleontologists. • Fossils tell us when, where, and how organisms lived. • Most Fossils are found in sedimentary rocks.
Conditions needed for fossil formation • For a dead organism to become a fossil it must be protected from scavengers and physically destructive things like waves and currents. • One way a dead organism can be protected is that sediments can bury it quickly . • Organisms with hard parts, like bones, shells, or teeth have a better chance of becoming fossils for 2 main reasons. 1) Scavengers are less likely to eat hard parts. 2) Hard parts take longer to decay.
Types of Preservation • Hard parts of organisms have tiny spaces within them. • Permineralized remains are fossils in which the spaces inside are filled with minerals from ground water.
Carbon Films • Tissues of organisms are made up of compounds. • As sediment piles up on dead organisms, the remains are subjected to pressure and heat. • A thin film of carbon is left that forms a silhouette of the original organism, called a carbon film. • Carbonized plants become coal.
Molds and Casts • Seashells and hard parts of organisms fall into the sediment. • They get buried by more sediment, and compaction and cementation change the sediment into rock. • The hard part might decay and leave behind a cavity called a mold. • Sediments or minerals might enter the mold and produce a cast, or copy of the original object.
Original Remains • Sometimes conditions allow the soft parts of organisms to be preserved. • Insects trapped in amber, a form of sticky tree sap. • Frozen ground and tar pits can also preserve organisms.
Trace Fossils • Fossilized tracks are evidence of an organism’s activities. • These can be tracks left in mud of stone. • Trails and burrows left by worms and other animals can tell you how they lived.
Index Fossils • Index fossils are the remains of species on Earth that: 1) Live short periods of time 2) were abundant 3) widespread geographically. • Scientists can estimate the ages of rock layers based on the index fossils they contain because they only lived during a specific time.
Fossils and Ancient Environments • Fossils can tell us: 1) The past climate of a region 2) Type of environment that existed when the rock layer formed.
