1. Fossils 2. Geographic Distribution 3. Homologies

What is a fossil? -The preserved remains of a once-living organism. How do fossils help scientists? 1. Tells us what organisms lived long ago 2. Shows how the Earth’s surface has changed. 3. Help us understand what past environments may have been like.

Over time, more sediment layers build on top of the remains. Minerals replace all or part of the organism’s body. The preserved remains may later become exposed by erosion or the Earth’s movement. Fossils are formed in SEDIMENTARY ROCK. If an organism dies and is buried by sediment rock, it’s bones are protected from rotting.

You have to DATE them!

1.Relative Dating Age of fossils RELATIVE to other rocks or fossils. 2. Radioactive dating ACTUAL age of fossils using the half life of radioactive isotopes

A B C D E Rock layers form in order of age – the oldest layers on the bottom and the youngest on the top. Scientists use index fossils to compare the ages of fossils. Index fossil: a species easily recognizable, existed for a short period of time, and wide geographic range. *** Does NOT give age in years***

A B C D E Looking at this mountain, where would you expect to find the oldest fossils?

Throughout an organism’s life, it takes in Carbon-14. Once the organism dies it no longer takes in Carbon-14. The C-14 present in the plant or animal begins to decay at a certain rate called half-life. Half-life: the length of time required for half the radioactive atoms in an organism to decay. Carbon-14 half life: 5,730 years

Carbon-14 is one example of radioactive dating. It is useful for dating fossils younger than 60,000 years. To date older rocks, researchers use elements with longer half-lives. Potassium-40 half-life: 1.26 billion years

How much of a 100g amount of carbon-14 would be left after 17,340 years? Carbon-14 half life: 5,730 Answer: 12.5g

Years from Present 05,73011,46017,19022,92028,65034,38040,11045,84051,570 Percent of Original C14 Remaining What do you notice about the percent of original C-14 remaining?

Similar animals in living different locations are the product of different lines of evolutionary descent.

Homologous Structure: structures that have different mature forms but develop from the same embryonic tissues. Homologous structures provide strong evidence that all four-limbed vertebrates have descended, with modifications, from common ancestors.

Not all homologous structures serve important functions. Vestigial organs: Organs in animals that are reduced in size to where they are just traces of homologous organs in other species.

Analogous Structure: the similarity of structure between two species that are not closely related. Which structures are analogous? Homologous? Answer: Analogous- Bird to Insect, Bat to Insect Homologous- bird and bat wings

Convergent Evolution: Species from different evolutionary branches may come to resemble one another if they live in very similar environments. Natural Selection may result in body structures and even whole organisms that look very similar without having the same common ancestor.

Comparative Embryology: the comparison of early stages of development Pharyngeal (throat) pouches in embryotic stages shows one sign that vertebrates evolved from a common ancestor. Pig Cow Rabbit Human

Molecular Biology studies amino acid sequences of similar proteins in different species to discover the molecular history of evolution and common ancestor.

Molecular Biology is the BEST WAY to determine how closely species are related to one another. Species 1ATGTAGC Species 2ATCTGAC Species 3AGGTACC Species 4AGGCGGC Which two species are most closely related based on these nucleotide sequences?