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1. Fossils 2. Geographic Distribution 3. Homologies.

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Presentation on theme: "1. Fossils 2. Geographic Distribution 3. Homologies."— Presentation transcript:


2 1. Fossils 2. Geographic Distribution 3. Homologies

3 1 st type of Evidence FOSSILS

4 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 Earths surface has changed. 3. Help us understand what past environments may have been like.

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

6 You have to DATE them!

7 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

8 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***

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


11 Throughout an organisms 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

12 Years from Present 05,73011,46017,19022,92028,65034,38040,11045,84051,570 Percent of Original C14 Remaining 100502512. What do you notice about the percent of original C-14 remaining?

13 What are the scientific explanations for data showing periods of stasis and sudden appearance in the fossil record? The fossil record suggests that evolution has proceeded at different rates for different organisms at different times.

14 Gradualism The idea that evolution involves a slow, steady change in a particular line of descent.

15 STASIS Showing very little change over time Example: Horseshoe crabs

16 Punctuated equilibrium Definition -Stable periods interrupted by rapid changes Rapid Evolution may occur because: A) small pop becomes isolated from the large population B)small group migrates to a new environment--FINCHES

17 2 nd type of Evidence Geographic Distribution

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

19 3 rd type of Evidence Homologies 3 types of Homologies Anatomical Molecular Developmental (embryology)

20 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.

21 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.

22 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

23 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.

24 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

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

26 Molecular Biology is the BEST WAY to determine how closely species are related to one another. Species 1ATGTAGCTG Species 2ATCTGACTC Species 3AGGTACCAG Species 4AGGCGGCAG Which two species are most closely related based on these nucleotide sequences?

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