The Geologic Time Scale

A Clock In the Rocks

Relative Dating

A technique used to determine the age of a fossil by comparing it to other fossils found in the layering of a rock

Sedimentary rock = undisturbed– Lower = oldest– Upper = newest

– Vertical geologic section.– Layer A is the oldest, layer C is the youngest.

C

B

A

Relative Dating (Cont)

Time of appearance and disappearance– Determines relative times of organisms

Problems with Relative Dating

Gaps in record Quality of Fossils

Relative Dating vs. Absolute Dating

Radioactive Dating

Absolute Dating Rocks

– Made of many elements Radioactive

– Elements that decay or break down at a steady and measurable rate

- Used to age fossils and layers of Earth

Radioactive dating

How is it measured?– Half-life- unit of

measurement of decay The amount of time

required for half of the radioactive atoms to decay

Radioactive Elements

Each element has a different half-life.

Radioactive Isotope

Half-Life

Rubidium- 87 50 billion years

Thoruim- 232 13.9 billion years

Uranium- 238 4.5 billion years

Potassuim- 40 1.3 billion years

Uranium- 235 713 million years

Carbon-14 5770

Carbon-14

Useful– Dates once living

material

Drawback– 60,000 years

Earth Age?

All this data helped scientists come to the conclusion the earth is 4.5 billion years old

Image Sources

http://3dparks.wr.usgs.gov/nyc/images/fig5.jpg http://static.howstuffworks.com/gif/carbon-14.gif http://qbx6.ltu.edu/s_schneider/courses/intro_astro/images/06-28.jpg http://qbx6.ltu.edu/s_schneider/courses/intro_astro/images/06-28.jpg http://www.uwlax.edu/MVAC/ProcessArch/ProcessArch/images/

stylesW.jpg http://upload.wikimedia.org/wikipedia/en/thumb/e/e8/Knightia.jpg/

250px-Knightia.jpg http://daneshnameh.roshd.ir/mavara/img/daneshnameh_up/4/4b/earth-

age.jpg http://evolution.berkeley.edu/evosite/lines/images/strat_column.gif