Earth’s Story

• James Hutton wrote Theory of the Earth.

• Uniformitarianism-states that the same geological processes shaping the Earth today have been working throughout the Earth’s history.

• “The present is the key to the past”

• Catastrophism-states that all geological change occurs suddenly.

• Many people thought that Hutton was crazy. They all thought that the changes on the Earth were sudden.

Debate

• At your tables number off by twos.

• The ones get together and the twos get together.

• Ones talk and make a list of why uniformitarianism should be accepted.

• Twos talk and make a list of why catastrophism should be accepted.

• In ten minutes you will debate with the others at your table supporting your case.

• The works of Charles Lyell helped to get uniformitarianism accepted.

• There are accounts of catastrophism (e.g. the asteroid that hit the Earth, that may have led to the extinction of the Dinosaurs).

Relative Dating

• Determining whether an object or event is older or younger than an object or event.

• Superposition-states that younger rocks lie above older rocks in undisturbed sequences.

• Geologic Column-

an ideal sequence that

contains all the known

fossils and rock

formations on Earth

arranged from oldest

to youngest.

Disturbed Rock Layers

• Fault-break in the Earth’s crust along which blocks of the crust slide relative to one another.

Disturbed Rock Layers

• Intrusion-molten rock from the Earth’s interior that squeezes into existing rock and cools.

Disturbed Rock Layers

• Folding-rock layers bend and buckle from the Earth’s internal forces.

Disturbed Rock Layers

• Tilting-internal forces in the Earth slant rock layers without folding them.

Unconformity

• A surface that represents a missing part of the geological column.

Fossils

• A naturally preserved evidence of life.

Ways that a fossil is formed or where they are found!!

• They are found in rocks!

• Minerals replace tissue

• Permineralization-minerals fill in pore spaces of an organism’s tissues

• Petrification-an organism’s tissues are completely replaced by minerals.

Formation and Location Continued

• They are found in amber.

• They are mummified.

Formation and Location Continued

• They are frozen.

• They are found in tar.

Types of Fossils

• Trace fossils-any naturally preserved evidence of an animal’s activity.

• Molds-a cavity in the ground or rock where a plant or animal was buried.

• Cast-an object created when sediment fills a mold and becomes a rock.

Cast and Mold

Fossils can tell time

• They can tell when there were changes in the environment.

• They also tell when there were changes in life-forms.

• Index fossils-fossils of organisms that lived during a relatively short, well-defined time span.

Time Marches On

• Geologic time scale-a scale that divides Earth’s 4.6-billion-year history into distinct intervals of time.

Divisions of Time

• Eons-the largest division of geological time.

• Eras-second-largest divisions of geological time.

• Periods-the third-largest division

• Epochs-the fourth-largest division

ERAS

• Paleozoic Era- “old life” lasted from about 540 to 248 million years ago. There were no land organisms.

• Mass extinction ended this era. Nearly 90 percent of all species perished.

ERAS Cont.

• Mesozoic Era- “middle life”. It lasted from about 248 to 65 million years ago. Age of the reptiles. By the end 50 percent perished.

ERAS Cont.

• Cenozoic Era- “recent life”. It began about 65 million years ago and continues to the present. It is called the Age of Mammals. Some mammals from the beginning of the era have now become extinct.