Dating & Fossils Pp 282-284 and 302-303

Geologic Dating Relative (qualitative): Determines if one thing is younger or older than another. Ex: Law of Superposition, use of index fossils, correlation of rock layers. Absolute (quantitative): Determines how many years old something is. Ex: Radiometric Dating

Absolute Dating Radiometric Dating = calculating the age of an object by measuring proportions of isotopes

Relative Dating Law of Superposition Younger rocks are on top, older rocks are on bottom. Lower layers must be in place before younger rocks can be deposited on top of them

FOSSILS Fossils are the preserved remains or traces of living things. Fossils provide evidence of how life has changed over time.

How are Fossils Formed? Fossils form when living things die and are buried by sediments. The sediments slowly harden into rock and preserve the shapes of the organisms

Types of Fossils Permineralization- minerals are deposited around or replace the hard structure Casts- flowing water removes all of original bones, leaving impression in sediment, then minerals fill in the mold

Trace fossils- record activity of organisms such as burrows, imprints of leaves, and footprints Amber- organisms trapped in tree resin that hardens Preserved remains- form when entire organism becomes encased in material such as ice, volcanic ash, or immersed in bogs.

The Fossil Record Fossils also help scientists infer how Earth’s surface has changed. Shows that fossils occur in a particular pattern. Older rocks contain fossils of simpler organisms. Younger rocks contain fossils of more complex organisms.

Provides evidence about the history of life on Earth. Fossils are clues to what past environments were like. Shows that different groups of organisms have changed over time.

Geologic Time Scale A system of chronological dating that relates geologic land forms (strata) to time. Shows sequence of major evolutionary events. Geologists have divided Earth’s history into time units based on the fossil record