Fossils Evidence of Past Life Fossils Fossils are

Fossils: Evidence of Past Life

Fossils • Fossils are the remains or traces of prehistoric life.

Fossils • Unaltered Remains • • Remains of organisms that haven’t changed, or have barely changed over time Name some examples or unaltered remains…

Fossils • Altered Remains • • • The remains of an organism are likely to be changed over time. Fossils can often become petrified (turned to stone) Molds and casts are also common fossils.

Fossils • Indirect Evidence • Trace fossils are indirect evidence of prehistoric life.

Fossils • Conditions Favoring Preservation • Two conditions are important for preservation: rapid burial and the possession of hard parts.

Dating with Radioactivity

Dating with Radioactivity • What is radioactivity? Radioactivity is the spontaneous decay of certain unstable atomic nuclei.

Radioactivity

Dating with Radioactivity • A half-life is the amount of time necessary for one-half of the nuclei in a sample to decay to a stable isotope.

Dating with Radioactivity • Every isotope decayschanges at a constant rate • Radiometric dating is calculating a rocks age by examining the amount radioactive isotopes present

Dating with Radioactivity • Radioactive isotopes decay (or change) into atoms called daughter products • Examples: • Carbon-14 decays to Carbon-12 • 1 half-life = 5, 730 years • Unranium-235 decays to Lead-207 • 1 half-life = 713 million years • Urannium-238 decays to Lead-206 • 1 half-life = 4. 5 billion years • Radiometric dating only works if the fossil has remained in a closed system since it became a fossil

The Half-Life Decay Curve

Radioactive Isotopes Frequently Used in Radiometric Dating

Dating with Radioactivity • Radiocarbon dating is done by comparing the amount of carbon-14 (an isotope of carbon) to the amount of carbon-12 (another carbon isotope) in a sample. • Half Life of Carbon-14 = 5, 730 years