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

 Radioactivity is the spontaneous decay of certain unstable atomic nuclei. What is radioactivity?

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 decays\changes at a constant rate Radiometric dating is calculating a rocks age by examining the amount radioactive isotopes present

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 half-life = 713 million years Urannium-238 decays to Lead half-life = 4.5 billion years Dating with Radioactivity 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

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. Dating with Radioactivity