What are fossils?• The remains, imprints or traces of an organism that lived long

ago.• Preserved in rock.

– Typically sedimentary rock– Must be buried quickly

• Types of fossils:– Molds– Casts– Carbonaceous film– Petrified remains– Original remains– Trace fossils

Hard parts decay leaving behind a cavity in the rockFormed when the mold becomes filled

Thin film of carbon forms outline on rock

Minerals replace the original organismThe actual organism is preserved

Evidence of organism activity (footprint)

Fossils in Sedimentary Rock

– Most fossils are preserved in sedimentary rock.

– Sedimentary rock usually forms when small particles of sand, silt, clay, or lime muds settle to the bottom of a body of water.

– As sediments build up, they bury dead organisms that have sunk to the bottom.

Fossils in Sedimentary Rock

– As layers of sediment continue to build up over time, the remains are buried deeper and deeper.

– Over many years, water pressure gradually compresses the lower layers and turns the sediments into rock.

How were entire organisms preserved?

• Original remains can be preserved in different materials.– Ice – Tar– Amber Tree sap

Iceman

What are fossil fuels?

• Raw fuel that comes from the remains of once living organisms– Solid – Liquid– Gas

Coal

Petroleum or Oil

Natural Gas or methane

Why do scientists study fossils?

• Clues to the past– Global changes & regional changes

• Environmental• Natural disasters• Climate change• Geologic• Evolution

How can relative age of rocks be determined?

• Using the law of superposition relative age can be determined

• Relative age is comparing one objects age to another.– If there are three layers

• Top is youngest• Then middle • Bottom is oldest

– Index fossil is always found in a particular layer

Relative Dating

– Lower layers of sedimentary rock, and fossils they contain, are generally older than upper layers.

– Relative dating places rock layers and their fossils into a temporal sequence.

Relative Dating – To help establish the relative ages of

rock layers and their fossils, scientists use index fossils. Index fossils are distinctive fossils used to establish and compare the relative ages of rock layers and the fossils they contain.

– If the same index fossil is found in two widely separated rock layers, the rock layers are probably similar in age.

“Who Killed the Iceman?”

• http://www.pbs.org/wgbh/nova/icemummies/iceman.html

• Picture & article

• http://www.pbs.org/wgbh/nova/transcripts/2518iceman.html

• http://wilderdom.com/evolution/OtziIcemanAlpsPictures.htm

How is absolute age determined?

• The specific age of a rock or fossil• Uses radioactive decay

– Half-life is the amount of time it takes for ½ of the mass of an element to decay into, more stable, element.

– The rate of decay can be measured– Particular elements have a constant rate of decay– Carbon-14 dating for living things– Not always 100% accurate

Geologic Time Scale

Geologic Time Scale

– Geologists and paleontologists have built a time line of Earth’s history called the geologic time scale.

– The basic divisions of the geologic time scale are eons, eras, and periods.

Divisions of the Geologic Time Scale

– The time scale is based on events that did not follow a regular pattern.

– The Cambrian Period, for example, began 542 million years ago and continued until 488 million years ago, which makes it 54 million years long.

– The Cretaceous Period was 80 million years long.

Naming the Divisions

– The Precambrian actually covers about 90 percent of Earth’s history.

– In this figure, the history of Earth is depicted as a 24-hour clock. Notice the relative length of Precambrian Time—almost 22 hours.

Physical Forces

– The theory of plate tectonics explains how solid continental “plates” move slowly above Earth’s molten core—a process called continental drift.

– Over the long term, continents have collided to form “supercontinents.” Later, these supercontinents have split apart and reformed.

Geological Cycles and Events

– Continental drift has affected the distribution of fossils and living organisms worldwide. As continents drifted apart, they carried organisms with them.

– For example, the continents of South America and Africa are now widely separated. But fossils of Mesosaurus, a semiaquatic reptile, have been found in both South America and Africa.

– The presence of these fossils on both continents, along with other evidence, indicates that South America and Africa were joined at one time.

Early Earth

The Earth is estimated to be 4.6 billion years old

Review of geologic time scale.

• Era• Periods• Epochs

PrecambrianPaleozoicMesozoicCenozoic

CambrianOrdovicianSilurianDevonianCarboniferousPermianTriassicJurassicCretaceousTertiaryQuaternary

PaleoceneEoceneOligoceneMiocenePliocenePleistoceneRecent

Geologic Time Scale(estimated years ago)

• 3.5 billion earliest evidence of life

• 540 million Paleozoic era begins

• 430 First land plant• 245 Mesozoic era

begins/Triassic period• 208 Jurassic period

• 225First Dinosaurs• 150 first birds• 146 Cretaceous period• 66 Dinosaurs extinct• 66 Cenozoic era• 60 Primates appear• 200,000 Humans