Key Words Fossil: the preserved remains or traces of living things Paleontologist a scientist who studies fossils to learn about organisms that lived long ago. sedimentary rock: the type of rock that is made of hardened sediment Petrified fossil: a fossil in which minerals replace all or part of an organism Mold: a fossil formed when an organism buried in sediment dissolves, leaving a hollow area. Cast: a fossil that is a copy of an organisms shape, formed when minerals seep into a mold. Carbon film: a type of fossil consisting of an extremely thing coating of carbon on rock. Trace fossil: a type of fossil that provided evidence of the activities of ancient organisms Scientific theory: a well-tested concept that explains a wide range of observation Evolution: the process by which all the different kinds of living things have changed over time. Extinct: describes a type of organism that no longer exists anywhere on Earth

Key Words Relative age: the age of a rock compared of the ages of rock layers Absolute age: the age of a rock given as the number of years since the rock formed. Law of superposition: the geologic principle that states that in horizontal layers of sedimentary rock, each layer is older than the layer above it and younger than the layer below it. Unconformity: a place where an old, eroded rock surface is in contact with a newer rock layer. Intrusion: an igneous rock layer formed when magma hardens beneath Earth’s surface. Extrusion: an igneous rock layer formed when lava flows onto Earth’s surface and hardens. Index fossil: fossils of widely distributed organisms that lived during only one short period. Radioactive decay: the breakdown of a radioactive element, releasing particles and energy

Essential Question How do scientist know that different kinds of plants and animals lived in Earth’s past? Journal your answer

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Evidence of Ancient Life  Fossils are the preserved remains or traces of living things.  Fossils provide evidence of how life has changed over time.  Fossils also help scientists infer how Earth’s surface has changed.  Fossils are clues to what past environments were like

Most fossils form when living things die and are buried by sediments. The sediments slowly harden into rock and preserve the shapes of the organisms. Water fossilization Land fossilization m/watch?v=SEDfRy6DQ ns HPA

Sedimentary Rock This is a rock type that is made of hardened sediment. Most fossils form from animals or plants that once lived in or near quiet water such as swamps, lakes, or shallow seas where sediments build up. When an organism dies, its soft parts often decay quickly or are eaten by animals. Thus, generally only hard parts leave fossils. These hard parts include bones, shells, teeth, seeds and woody stems. It is rare for the soft parts of an organism to become a fossil.

Types of Fossils

Petrified fossils A fossil may form when the remains of an organism become petrified. A fossil may form when the remains of an organism become petrified. The term petrified means “turning into stone”. The term petrified means “turning into stone”. Petrified fossils are fossils in which minerals replace all or part of an organism. Petrified fossils are fossils in which minerals replace all or part of an organism. Petrified Wood: formed after sediment covered the wood. Then water rich in dissolved minerals seeped into spaces in the plant’s cells. Over time, the water evaporated, leaving the hardened minerals behind. Some of the wood remains but he minerals have hardened and preserved it formed after sediment covered the wood. Then water rich in dissolved minerals seeped into spaces in the plant’s cells. Over time, the water evaporated, leaving the hardened minerals behind. Some of the wood remains but he minerals have hardened and preserved it.

Molds and Casts Most common fossils are molds and casts Copy the shape of ancient organisms Mold is hollow area in sediment in the shape of an organism or part of an organism Forms when the hard part of the organism, such as a shell, is buried in sediment. Water carries dissolved minerals and sediment into the empty space of the mold. If the water deposits the minerals and sediment a cast is formed. A copy of the shape of an organism. Cast is the opposite of a mold Watch the animations then take the quizzes hill.com/sites/dl/free/ /164155/ html hill.com/sites/dl/free/ /164155/ html landforms/fossils.htm landforms/fossils.htm

Trace fossils Most types of fossils preserve the shapes of ancient animals and plants. Most types of fossils preserve the shapes of ancient animals and plants. Trace fossils provide evidence of the activities of ancient organisms. Trace fossils provide evidence of the activities of ancient organisms. A fossilized footprint print is one example of a trace fossil A fossilized footprint print is one example of a trace fossil Trace fossils provide clues about an animals size and behavior. How fast could the animal move. Did it walk on two or four legs? Did it live alone or in a pack. Trace fossils provide clues about an animals size and behavior. How fast could the animal move. Did it walk on two or four legs? Did it live alone or in a pack. silintro/ silintro/

Relative age of rocks and Index Fossils

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