Topic 13 Earth History

Estimated age of the Earth: 4.6 billion years 4.6 x 109 years 4,600,000,000 years See ref. tables p. 8

Putting events into order based on when they occurred. Absolute Dating Relative Dating Putting events into order based on when they occurred. Absolute Dating Actual age of the rock, fossil or event Vs.

Relative Dating: Sequence of Events: Law of superposition The age of the rock increases as you move down the rock column. Diagram: Except when the rocks have been overturned or thrust faulted

Folding/ Faulting/ Tilting All are younger than the rocks they appear in. Drawing:

Igneous Intrusions/ Extrusions They are younger than the rocks they intrude into or extrude onto. Drawings:

Internal Characteristics of Rock Sediments are older than the rock in which they are found. Xenoliths- igneous rocks that contain pieces of other rocks. The pieces are older Veins- mineral veins are younger than the rocks they form in

Unconformities Buried erosional surfaces Represents a gap in the rock record. Drawing:

Absolute Dating Radiometric Dating Radioactive Isotope An isotope of an element that is unstable and breaks down (decays) into another element. Daughter Product The stable end product of radioactive decay.

Half-Life The amount of time it takes for ½ of a radioactive isotope to decay.

Carbon 14 can only be used to find the age of stuff that is relatively young (50,000 years or less). NOTHING can change the rate of radioactive decay!!!

Fossils: Remains or traces of past life preserved in the rock record. Fossils usually form from organisms… That have hard parts That were buried rapidly.

Information from Fossils Types of life Crustal plate positions Past environments Evolution Index Fossils Existed for a short period of time Widespread and abundant

Fossil evidence suggests that a wide variety of plants and animals have lived on Earth and most have become extinct. An even greater number of organisms were probably never fossilized.

Correlation: The process of showing that rock strata (layers) or geologic events in different places are the same age. Techniques for correlation: Direct observation (looking at them!) Similar composition Volcanic ash deposits (cover a large area in a short time) Index fossils Widespread and abundant Existed for a short period of geologic time