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Chapter 9.1: Fossils

Mr. Perez

Paleontologist Fossil Permineralized remains Carbon film Mold Cast Index fossil Trace fossil

Important vocabulary

A paleontologist is a scientist who studies fossils.

They can learn about extinct animals from their fossil remains

Paleontologists can use fossils to study the similarities and differences of organisms that lived in the past and compare them with those living today.

Traces of the Distant Past

Sedimentary rock may contain fossils of plants, animals and even some microbes.

Fossils are the remains, imprints, or traces of prehistoric organisms

Fossils have helped scientists determine approximately when life first lived on land, and when organisms became extinct– they are evidence of not only when and where organisms lived, but also HOW they lived.

Formation of Fossils

Conditions needed to form fossils: Protection from scavengers and

agents of physical destruction (waves, currents, wind) Usually, a dead organism is protect

by being buried under sediments Dead organisms should have hard

tissues such as bones, shells or teeth Scavengers are less likely to eat

these hard parts These hard tissues also decay (break

down) more slowly than softer tissue

Formation of Fossils

Formation of Fossils

Mineral Replacement Carbon Films Coal Molds and Casts Original Remains Trace Fossils

Types of Preservation

Most hard tissues of an organism have empty spaces inside

Permineralized remains are fossils in which the spaces inside are filled with minerals from groundwater

Some original material from the fossil organism’s body might be preserved– sometimes, DNA can be extracted

Mineral Replacement

Tissues of organisms are made of carbon As an organism is buried, heat and

pressure squeeze gases and liquids out A carbon film forms when a thin residue

is left, forming a silhouette of the original organism

Carbon Films

Large amounts of plant matter accumulates in swampy areas…

After millions of years, these deposits become completely carbonized as COAL

We use coal for fuel Coal is not a very good fossil to inform us

of the plant’s past

Coal

Impressions form when seashells or other hard parts of organisms fall into a soft sediment such as mud—which is buried by more sediment

Compaction and cementation turns this sediment into a sedimentary rock

Sometimes, there are holes in the rock that allow water and air to dissolve the hard part of the organism inside the rock, leaving a cavity called a mold

Later, mineral-rich water or other sediment might enter the cavity, form new rock and produce a copy or a cast of the original objectMolds and

Casts

Molds and Casts

Sometimes conditions allow original soft tissue of organisms to be preserved for thousands or millions of years.

Insects trapped in amber (hardened form of tree resin/sap)

Mammoths preserved in frozen ground in Siberia

Natural tar deposits, such as La Brea tar pits in California

Original Remains

Trace fossils are fossilized tracks and other evidence of the activity of organisms

Tracks can tell you more about HOW and organism lived than any other type of fossil

Trails and burrows can also tell scientists about how animals lived

Trace Fossils

Species have changed over time Fossils help provide evidence of similarities and

differences of organisms that lived in the past with those living today.

Some species have remained the same for very long periods of time, whereas some other species have changed a lot

These changing species are used as index fossils, or remains of species that existed

1. on Earth for relatively short periods of time2. were abundant3. were widespread geographically

Index Fossils

We can use index fossils to estimate the age of rock layers

Index Fossils

Fossils help scientists determine whether an area was land or whether it was covered by an ocean at a particular time

Fossils can also help determine the climate of a past region

Fossils and Ancient Environments

Today, we will be starting a 2 day lab. This lab will help demonstrate how fossils are formed.

Each group should have the following MATERIALS: Paper towels Three slices of bread (one slice each of

white, wheat, and grain) 6 Gummy candy fish (or other gummy sea

animals or plants) Heavy books Clear drinking straws (Day 2 only)

Fossil Formation Lab

PROCEDURE (Day 1)1. Remove and throw away the crust of each slice of bread2. Place the slice of white bread on top of one paper towel. Place

THREE gummy bears on top of the slice of bread. This represents the sandy sea floor with a dead organism.

3. Place the slice of grain bread on top of your white bread layer. This represents sediments deposited on top of dead material and settling on the bottom of the ocean.

4. Place the remaining gummy bears on top of the grain bread layer and the wheat bread on top of the gummy bears. This represents more dead material and sediments that are deposited on top of the bottom layers.

5. Fold over your paper towel, covering your stack of bread and gummy bears.

6. Place a textbook on top of your bread stack to represent pressure applied to the dead matter. Leave it under the text book for 2 days.

Fossil Formation Lab

Fossil Formation Lab

PROCEDURE (Day 2)1. Observe the bread fossil. Push a clear straw straight down

into the bread and pull it back up to “extract” a core sample. Observe the layers through the straw.

2. Try to separate the layers of the bread. 3. Try to extract the bears. 4. Compare the colored residue of the gummy bear in the

bread fossil to the remains of the plants and animals that seep into rock. The residue left by the gummy bear represents oil deposits left behind by dead ocean plants and animals. Over millions of years, these remains are pressurized to become oil and natural gas deposits.

Fossil Formation Lab

Florida Science Grade 7Glencoe Science & McGraw Hill

Publishing Google Images http://www.earthsciweek.org/forteacher

s/2009/FossilFormation_Sept_cont.html

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