A Trip Through Geologic TimeA Trip Through Geologic Time

FossilsFossilsFossilsFossils are are preserved remains or preserved remains or traces of living things.traces of living things.

Most fossils form Most fossils form when living things die when living things die and are buried by and are buried by sediments. sediments.

The sediments slowly The sediments slowly harden into rock and harden into rock and preserve the shape of preserve the shape of the organisms.the organisms.

Scientists who study Scientists who study fossils are fossils are paleontologists.paleontologists.

FossilsFossilsFossils are usually Fossils are usually found in found in sedimentarysedimentary rocks. rocks.

When an organism When an organism dies, its soft parts dies, its soft parts often decay quickly often decay quickly leaving only the leaving only the hard parts to hard parts to fossilize.fossilize.

Ex. Bones, Shells, Ex. Bones, Shells, Teeth, or SeedsTeeth, or Seeds

Kinds of FossilsKinds of FossilsPetrified FossilsPetrified Fossils: : fossils in which fossils in which minerals replace all or minerals replace all or part of the organism. part of the organism. Ex: petrified woodEx: petrified woodWhen the object is When the object is buried by sediment, buried by sediment, water rich in minerals water rich in minerals seeps into the cells. seeps into the cells. After the water After the water evaporates, hardened evaporates, hardened minerals are left minerals are left behind.behind.

Kinds of FossilsKinds of Fossils Molds and Molds and CastsCasts

A A moldmold is a is a hollow area in hollow area in sediment in the sediment in the shape of an shape of an organism or part organism or part of an organism.of an organism.

A A castcast is a copy is a copy of the shape of of the shape of an organism.an organism.

Kinds of FossilsKinds of FossilsCarbon FilmsCarbon Films:: an an extremely thin coating extremely thin coating of carbon on rock that of carbon on rock that forms when materials forms when materials that make up an that make up an organism become organism become gases and escape gases and escape leaving only carbon leaving only carbon behind.behind.Trace FossilsTrace Fossils provide evidence of provide evidence of the activities of the activities of ancient organisms. ancient organisms. Ex: footprints, animal Ex: footprints, animal trails, or animal trails, or animal burrows.burrows.

Kinds of FossilsKinds of Fossils

Preserved Preserved RemainsRemains are are formed when an formed when an organism is organism is preserved with little preserved with little or no change.or no change.

For example when For example when organisms become organisms become preserved in tar, preserved in tar, amber (tree sap), amber (tree sap), and freezing.and freezing.

Why Study Fossils?Why Study Fossils?Scientists study Scientists study fossils to learn what fossils to learn what past life forms were past life forms were like.like.

Paleontologists Paleontologists classify organisms in classify organisms in the order in which the order in which they lived.they lived.

All the information All the information scientists have scientists have gathered is called the gathered is called the fossil recordfossil record..

Fossil RecordFossil RecordThe fossil record The fossil record provides evidence provides evidence about the history of about the history of life on Earth.life on Earth.The fossil record The fossil record also shows how also shows how different groups of different groups of organisms have organisms have changed over time.changed over time.It also provides It also provides evidence to support evidence to support the theory of the theory of evolution.evolution.

Remember!Remember!A scientific theory is A scientific theory is a well-tested concept a well-tested concept that explains a wide that explains a wide range of range of observations.observations.

The fossil record The fossil record shows that millions shows that millions of types of of types of organisms have organisms have evolved. evolved.

However, many However, many others became others became extinct.extinct.

Finding the Age of Rocks Through Finding the Age of Rocks Through Rock DatingRock Dating

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Ages of RocksAges of RocksThe The relative agerelative age of of a rock is its age a rock is its age compared to other compared to other rocks. rocks. Use words like: Use words like: “older or younger”“older or younger”The The absolute ageabsolute age of a rock is the of a rock is the number of years number of years since the rock was since the rock was formed. formed. Ex: 358-360 myaEx: 358-360 mya

Rock Joke!!Rock Joke!!

What does a rock want What does a rock want to be when it grows to be when it grows up?up?

A Rock Star!!A Rock Star!!

The Position of The Position of Rock LayersRock Layers

It can be difficult to It can be difficult to determine a rocks determine a rocks absolute age. So… absolute age. So… scientists use the scientists use the law law of superpositionof superposition..

According to the According to the law law of superpositionof superposition, in , in horizontal horizontal sedimentary rock sedimentary rock layers the oldest layer layers the oldest layer is at the bottom. Each is at the bottom. Each higher layer is higher layer is younger than the younger than the layers below it.layers below it.

Rock Joke!!Rock Joke!!

How do rocks wash How do rocks wash their clothes?their clothes?

The Rock Cycle!!The Rock Cycle!!

Other Clues to Other Clues to Relative AgeRelative Age

Clues From Clues From Igneous RockIgneous Rock

Lava that cools at the Lava that cools at the surface is called an surface is called an extrusion. Rock extrusion. Rock below an extrusion is below an extrusion is always older.always older.

Magma that cools Magma that cools beneath the surface beneath the surface is called an intrusion. is called an intrusion. An intrusion is An intrusion is always younger than always younger than the rock layers the rock layers around an beneath it.around an beneath it.

Other Clues to Relative AgeOther Clues to Relative AgeFaultsFaults (a break in the (a break in the rock) are always rock) are always younger than the younger than the rock it cuts through!rock it cuts through!UnconformitiesUnconformities: An : An unconformity is a unconformity is a gap gap in the geological in the geological recordrecord that can occur that can occur when erosion wears when erosion wears away rock layers and away rock layers and other rock layers other rock layers form on top of the form on top of the eroded surface.eroded surface.

Using Fossils to Date Rocks!Using Fossils to Date Rocks!Scientists use index Scientists use index fossils to match rock fossils to match rock layers. layers.

An An index fossilindex fossil must must be widely distributed be widely distributed and represent a type and represent a type of organism that of organism that existed only briefly.existed only briefly.

They are useful They are useful because they tell the because they tell the relative agesrelative ages of the of the rock layers they are rock layers they are found in.found in.

The TrilobiteThe Trilobite

One example of an index One example of an index fossil is a trilobite.fossil is a trilobite.

Trilobites were a group of Trilobites were a group of hard-shelled animals hard-shelled animals whose bodies had three whose bodies had three distinct parts.distinct parts.

They evolved in shallow They evolved in shallow seas more than 500 seas more than 500 million years ago.million years ago.