FossilsFossils

Essential Questions:Essential Questions:What are fossils and how are they formed?What are fossils and how are they formed?What are the different kinds of fossils?What are the different kinds of fossils?What do fossils tell about how organisms have What do fossils tell about how organisms have changed over time?changed over time?

How do fossils form?How do fossils form?

Fossils are the preserved remains Fossils are the preserved remains or traces of living things.or traces of living things.– Fossils provide evidence of how life Fossils provide evidence of how life

has changed over time.has changed over time.– Fossils also help scientists infer how Fossils also help scientists infer how

Earth’s surface has changed.Earth’s surface has changed.– Fossils are clues to what past Fossils are clues to what past

environments were like.environments were like.

How do fossils form?How do fossils form?

Most fossils form when living Most fossils form when living things die and are buried by things die and are buried by sediments. The sediments slowly sediments. The sediments slowly harden into rock and preserve the harden into rock and preserve the shapes of the organisms.shapes of the organisms.

How do fossils form?How do fossils form?

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

How do fossils form?How do fossils form?

Fossils are Fossils are usually found in usually found in sedimentary sedimentary rock.rock.

Sedimentary rock Sedimentary rock is the type of is the type of rock that is made rock that is made of hardened of hardened sediment.sediment.

What are the different What are the different kinds of fossils?kinds of fossils?

Fossils found in rock include Fossils found in rock include petrified fossils, molds and casts, petrified fossils, molds and casts, carbon films, and trace fossils.carbon films, and trace fossils.

Other fossils form when the Other fossils form when the remains of organisms are remains of organisms are preserved in substances such as preserved in substances such as tar, amber, or ice.tar, amber, or ice.

What are the different What are the different kinds of fossils?kinds of fossils?

Petrified FossilsPetrified Fossils– A fossil may form A fossil may form

when the remains of when the remains of an organism an organism become petrified.become petrified.

– Petrified means Petrified means “turning to stone”“turning to stone”

– Petrified fossils are Petrified fossils are fossils in which fossils in which minerals replace all minerals replace all or part of an or part of an organism.organism.

What are the different What are the different kinds of fossils?kinds of fossils? Molds and castsMolds and casts

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

A mold forms when the hard part of the organism A mold forms when the hard part of the organism such as a shell, is buried in sediment.such as a shell, is buried in sediment.

– A cast is a copy of the shape of an organism.A cast is a copy of the shape of an organism. Water carrying dissolved minerals and sediment Water carrying dissolved minerals and sediment

may seep into the empty space of a mold. If the may seep into the empty space of a mold. If the water deposits the minerals and sediment there, water deposits the minerals and sediment there, the result is a cast.the result is a cast.

Molds and CastsMolds and Casts

What are the different What are the different kinds of fossils?kinds of fossils? Carbon filmsCarbon films

– An extremely thin coating of carbon on An extremely thin coating of carbon on rock.rock.

HOW DOES A CARBON FILM FORM?HOW DOES A CARBON FILM FORM?– When sediment buries an organism, some When sediment buries an organism, some

of the materials that make up the of the materials that make up the organism can become gases. These gases organism can become gases. These gases escape from the sediment, leaving carbon escape from the sediment, leaving carbon behind. Eventually, only a thin film of behind. Eventually, only a thin film of carbon remains.carbon remains.

Carbon FilmsCarbon Films

What are the different What are the different kinds of fossils?kinds of fossils? Trace fossilsTrace fossils

– Trace fossils provide evidence of the Trace fossils provide evidence of the activities of ancient organisms.activities of ancient organisms.

– A fossilized footprint is on example A fossilized footprint is on example of a trace fossil. of a trace fossil.

– Other examples of trace fossils Other examples of trace fossils include the trails that animals include the trails that animals followed or the burrows that they followed or the burrows that they lived in.lived in.

Trace FossilsTrace Fossils

What are the different What are the different kinds of fossils?kinds of fossils? Preserved RemainsPreserved Remains

– Some processes preserve the remains Some processes preserve the remains of organisms with little or no change.of organisms with little or no change.

Some remains are preserved when Some remains are preserved when organisms become trapped in tar.organisms become trapped in tar.

Ancient organisms also have been Ancient organisms also have been preserved in amber. Amber is the preserved in amber. Amber is the hardened resin, or sap, of evergreen trees.hardened resin, or sap, of evergreen trees.

Freezing is another way in which remains Freezing is another way in which remains can be preserved.can be preserved.

Preserved RemainsPreserved Remains

What do fossils tell about how What do fossils tell about how organisms have changed over organisms have changed over time?time?

The fossil record provides evidence The fossil record provides evidence about the history of life on Earth. The about the history of life on Earth. The fossil record also shows that different fossil record also shows that different groups of organisms have changed groups of organisms have changed over time.over time.

The fossil record reveals a surprising The fossil record reveals a surprising fact: fossils occur in a particular order.fact: fossils occur in a particular order.– Older rocks contain fossils of simpler Older rocks contain fossils of simpler

organisms. Younger rocks contain fossils organisms. Younger rocks contain fossils of more complex organisms.of more complex organisms.

– In other words, the fossil record shows that In other words, the fossil record shows that life on Earth has evolved, or changed. life on Earth has evolved, or changed.

What do fossils tell about What do fossils tell about how organisms have how organisms have changed over time?changed over time? The fossil record provides evidence to The fossil record provides evidence to

support the theory of evolution.support the theory of evolution. A scientific theory is a well-tested A scientific theory is a well-tested

concept that explains a wide range of concept that explains a wide range of observations.observations.

Evolution is the gradual change in living Evolution is the gradual change in living things over long periods of time.things over long periods of time.

The fossil record shows that millions of The fossil record shows that millions of types of organisms have evolved. types of organisms have evolved. – But many others have become extinct.But many others have become extinct.– A type of organism is extinct if it no longer A type of organism is extinct if it no longer

exists and will never again live on Earth.exists and will never again live on Earth.

What do fossils tell about What do fossils tell about how organisms have how organisms have changed over time?changed over time? Paleontologists use fossils to build Paleontologists use fossils to build

up a picture of Earth’s up a picture of Earth’s environments in the past.environments in the past.

Fossils also provide evidence of Fossils also provide evidence of Earth’s climate in the past.Earth’s climate in the past.

Scientists can use fossils to learn Scientists can use fossils to learn about changes in Earth’s surface.about changes in Earth’s surface.

In SummaryIn Summary

Most fossils form when living things die Most fossils form when living things die and are quickly buried by sediment, and are quickly buried by sediment, which eventually hardens and which eventually hardens and preserves parts of the organisms.preserves parts of the organisms.

The major kinds of fossils include The major kinds of fossils include petrified remains, molds, casts, carbon petrified remains, molds, casts, carbon films, trace fossils, and preserved films, trace fossils, and preserved remains.remains.

The fossil record shows that many The fossil record shows that many different organisms have lived on Earth different organisms have lived on Earth at different times and that groups of at different times and that groups of organisms have changed over time.organisms have changed over time.

Fossils

Preserved fossils Rock Fossils

amber tar ice Trace fossils Casts and molds Petrified fossils Carbon films