Evidence of Evolution Direct Evidence Indirect Evidence
Direct Evidence • Visible evidence that organisms have changed over time • Ex. – Fossils
Fossils • Paleontologists: scientists who study fossils. • Provides incomplete information about the history of life. • Over 99% of all species that have lived on Earth have become extinct.
How Fossils Form Dead organisms are buried by layers of sediment, which forms new rock.
How Fossils Form The preserved remains may be later discovered and studied.
Dating Fossils • Relative Dating • Age is determined by the layers of rock. • Rock layers form in order by age—the oldest on the bottom, with more recent layers on top.
Dating Fossils • Radioactive dating • Radioactive elements steadily break down into non-radioactive elements. • Half-lives determine the age of a sample. • Half-life - time required for half of the atoms to decay.
Half-life of Radioactive Isotopes • C-14 breaks down into N-14. • The half life of C-14 is 5,760 years. • Comparing the amount of C-14 to N-14 can determine the age of the fossil
Radioactive Dating • A fossil has 50% C-14 and 50% N-14 • The fossil should be 5,760 years old. • If another 5,760 years passed, what would be the ratio of C-14 to N-14? • Right!!.........C-14 25% to N-14 75%
What about transitional fossils? A B C D F G H I 1 2 3 4 5 6 8 9
Indirect Evidence of Evolution • Evidence that suggests organisms have common ancestry. • Embryological Similarities
Indirect Evidence of Evolution • 2. Comparative Morphology • (Homologous Structures)
Indirect Evidence of Evolution • 3. Similarities in Biochemistry • DNA similarities (98% of our DNA is the same as a chimpanzee) • Protein in all organisms is composed of the same 20 amino acids!!
Evidence of Evolution • Direct Evidence – something we can look at that takes us back in time. • Ex. Fossils • Indirect Evidence – something we can look at that show some kind of evolutionary connection between organisms. • Ex. Embryological similarities, Homologous structures, Biochemistry similarities