The Fossil Record

What is a fossil? Preserved remains or evidence of an ancient organism

Fossil Formation An organism dies and is covered with sand, silt, clay or volcanic ash. The particles covering the organism prevent decay. The particles and the organism become part of the rock.

Dating Fossils Two ways to date a fossil Relative dating Comparing the age of the fossil to other fossils Absolute dating Finding the age in years of the fossil.

Methods of Relative Dating Older fossils are found beneath younger fossils Use of index fossils- an easily recognized, widespread fossil found in a short time period.

Method for Absolute Age Radioactive Dating Some naturally occurring elements are radioactive and undergo decay. The half-life, or amount of time it takes for ½ of the material to decay, is known.

Method for Absolute Age Radioactive dating By determining the amount of the radioactive material in the fossil, the age of the fossil can be calculated.

Geologic Time Scale Scale used to represent evolutionary time scale. In the 19th century, geologists had determined which groups of rocks came from the same time period because of similar fossils.

Geologic Time Scale Rock system- groups of rocks that came from the same time period with similar fossils. Period – the time period that covered one system of rock.

Geologic Time Scale Era – longest unit of the time scale; contains 2 or more periods.