1. Chapter 25

2. How did life arise on a planet with no organic compounds? Involved four stages 1) Abiotic synthesis of small organic molecules (amino acids and nitrogenous bases) 2) Joining of these molecules into macromolecules 3) Packaging of large molecules into protocells 4) Origin of self replicating molecules that made inheritance possible

3. Earth is about 4.6 billion year old How did the earth get here? Formed by a condensing nebula Material pulled together Collisions caused the formation of planets

4. Earth was very hot, violent first 700 million years Many objects struck Earth releasing heat – kept Earth in a molten state Objects eventually separated into layers Hydrogen, carbon monoxide, water vapor, methane, and carbon dioxide released Oxygen not released until about 2 billion years ago

5. Miller-Urey Experiment Lightning strikes caused inorganic molecules to form organic molecules Electricity applied to these inorganic molecules led to the production of amino acids

6. Meteorite Hypothesis Amino acids have been found in meteorites Suggests that amino acids could have been present when Earth formed

7. Presence of small organic molecules is not enough for emergence of life Need catalysts to and other proteins to drive the combination 2009 study showed abiotic synthesis of RNA can occur spontaneously from small precursor molecules

8. Organisms need an environment or “shelter” to carry out replicative processes Protocells Can form spontaneously when lipids and other organic molecuels are added to water Organisms could then carry out many life sustaining functions

9. RNA – Early Genetic Material Ribozymes – RNA molecules that can catalyze chemical reactions Can make enzymes that would cut itself, copy itself, and make more of itself Short chains of RNA can form from inorganic molecules

10. Relative Dating Estimates the time an organism was alive based upon it’s placement in rock layers Allows for inferences of species origin Does not provide actual age dating of fossil

11. Radiometric Dating Estimates actual or absolute age Calculation of the age of a sample based upon the amount of remaining radioactive isotopes Half life The amount of time it takes for half of the iostopes in a sample to decay into another element Different items have different half lives

12. Carbon-14 Dating Good for recent remains Carbon-14-taken up by organisms while they are alive C-14 begins to break down when organism dies Researchers compare the amount of Carbon-14 to Carbon-12 or Nitrogen-14 The larger the ratio of C-14 to C-12 (or N-14), the older the organism Uranium-238 Good - Half-life of 4.5 billion years Bad – living organisms do not take up uranium Use of indirect radiometric dating will work Look at fossils wedged between two layers of volcanic ash

13. Index Fossils Easily recognized and the species must have existed for a short period, but have a wide geographic range It will only be found in a few layers, but they will be specific and in different locations Trilobite

14. Earliest evidence of life in fossil record is 3.5 billion years ago Stromatolites Layered rocks that form when certain prokaryotes bind thin films of sediment

15. Oxygen Revolution Levels on Earth increased from 1% to 10% of present level Probably due to ancient cyanobacteria Early oxygen would have dissolved into the oceans Would have taken time for the oceans to become effectively saturated and then “gas out”

16. Early prokaryotes are considered the ancestors of eukaryotes Early on some smaller prokaryotes began to enter into other prokaryotes Endosymbiotic Theory Eukaryotic cells arose from living communities formed by prokaryotic cells

17. Evidence of the Endosymbiotic Theory Mitochondria and chloroplasts: Contain DNA similar to bacterial DNA Have ribosomes whose structure and size closely resemble bacterial ribosome Reproduce by binary fission These three key pieces of evidence are what give credence to the idea that eukaryotes formed from prokaryotes

18. Occurred 525-535 million years ago Fossils of sponges, cnidarians, and mollusks Prior to this most animals were suspension or filter feeders Cambrian period brought about predation

19. Cyantobacteria and algaea began to coated damp terrestrial surfaces over 1 billion years ago This lead to fungi, plants, and eventually animals arising ~500 mya

20. 5 mass extinctions The Permian and Cretaceous are most well known Each extinction resulted in 50% or more of Earth’s marine species becoming extinct

21. Living organisms have diversified over the last 250 million years Caused by adaptive radiation Evolutionary change where organisms form many new species Adaptations allow them to fill different ecological niches Ex. Mammals worldwide, Galapagos finches, African cichlids

22. Evolutionary changes in body form can be due to changes in rate and timing or spatial patterns Heterchrony – change in the rate or timing of body structures during embryonic development Spatial patterns can be changed by altering homeobox genes