2. Overview  Geologic events that alter environments change the course of biological evolution  Example: Large lake splitting into several small lakes  Living things change the planet they inhabit  Example: Evolution of photosynthetic organisms putting oxygen into the atmosphere

3. Photosynthetic Cyanobacteria

5. 26.1  Cells produced in 4 stages  1. Abiotic synthesis of AA & nucleotides (organic compounds)  2. Joining of monomers into polymers  3. Packaging into protobionts – droplets with membranes that maintained an internal chemistry different from the environment.  4. Origin of replication that made inheritance possible  Evidence for each of these 4 stages discussed

6. 1. Synthesis of organic compounds  Earth formed about 4.6 billion years ago  Conditions on early Earth were very different from today  “Primitive soup” experiment of Miller and Urey  Strongly reducing atmosphere  Hydrogen  Methane  Ammonia  Water vapor  Sparks to mimic lightning

7. Conception of Earth 3 billion years ago

8.  Extraterrestrial Sources of Organic Compounds  Amino acids that reached early Earth aboard chondrites could have added to the primitive soup  Looking to other planets for signs of life  Present day Mars = no life  Billions of years ago it was warm, liquid water, and carbon dioxide in the atmosphere

9. 2. Abiotic synthesis of polymers  Researchers have produced amino acids polymers by dripping solutions of amino acid monomers onto hot sand, clay, or rock  Formed spontaneously

10. 3. Protobionts  Replication and metabolism are essential for life  Protobionts: aggregates of abiotically produced molecules surrounded by a membrane or membrane-like structure.  Exhibit some properties of life and could have formed from abiotically produced organic compounds

11. 4. Origin of replication  The first genetic material was probably RNA  Had the ability to copy itself and began to appear in protobionts  RNA could have been the template on which DNA was assembled  DNA is much more stable and can be replicated more accurately so as genomes grew DNA grew  RNA world gave way to a DNA world and RNA took over its role that we see it in today

12. 26.2 The fossil record  Fossils are found in sedimentary rocks  Index fossils: the strata at one location can often be correlated with strata at another location by the presence of similar fossils known as index fossils

13. Radiometric dating  Radiometric dating: decay of radioactive isotopes  Half-life: the number or years it takes for 50% of the original sample to decay

14.  Carbon-14 has a half life of 5,730 years so it is useful for dating fossils up to about 75,000 years old  Potassium-40 used to date much older fossils (530 million years old)  Magnetism of rocks can also provide dating information

15. Geologic record  3 Eons  Archaean & Proterozoic lasted approx. 4 billion years  These are known as Precambrian  Phanerozoic eon –the last half billion years is most of the time multicellular eukaryotic life has existed  Divided into 3 eras  Paleozoic  Mesozoic  Cenozoic  Boundaries between eras correspond to times of mass extinctions seen clearly in the fossil record

17. Mass Extinctions  2 mass extinctions have received the most attention  Permian & Cretaceous  Permian – at the boundary between Paleozoic and Mesozoic eras claimed about 96% of marine animal speices  Cretaceous – at the boundary between Mesozoic and Cenozoic eras doomed more than half of all marine species and many families of terrestrial plants and animals including the dinosaurs.

18.  Permian mass extinction caused by volcanic eruptions that increased the carbon dioxide and warmed the global climate  Cretaceous mass extinction caused by an asteroid or comet hitting the earth that spewed up dust and blocked sunlight for several months.

19. Impact Crater

20. 26.3  Oldest known fossils  Date to 3.5 billion years ago  Stromatolites  Composed of layers of bacteria and sediment  Found today in a few warm, shallow, salty bays

21. Prokaryotes  Prokaryotes were Earth’s sole inhabitants  3.5 to about 2 billion years ago

22. The oxygen revolution  Earliest types of photosynthesis did not produce oxygen  Oxygenic photosynthesis evolved 3.5 billion years ago in cyanobacteria  When oxygen started to accumulate in atmosphere  It posed a challenge for life  It provided an opportunity to gain abundant energy from light  It provided organisms an opportunity to exploit new ecosystems

23. 26.4 – Eukaryotes  Oldest fossil eukaryotes date back 2.1 billion years  Arose from Endosymbiosis and genetic exchanges between prokaryotes  Endosymbiotic theory states that chloroplasts & mitochondria were formerly prokaryotic organisms living within larger cells.

24. Endosymbiosis  Mitochondria and plastids were formerly small prokaryotes living within larger host cells  Gained entry to the host cell as undigested prey or internal parasites  The host and endosymbionts would have become a single organism  Evidence to support theory:  Similarities in inner membrane structures and functions  Both have their own circular DNA

25. 26.5 - Multicellularity  Evolved several times in eukaryotes  Oldest fossils of eukaryotes, small algae that lived 1.2 billion years ago  1 st multicellular organisms were colonies

26. Cambrian Explosion  Most of the major phyla of animals appear here

27. Colonization of land by plants, fungi, and animals  Occurred about 500 million years ago  Adaptations that helped prevent dehydration made it possible to move out of water onto land  Symbiotic relationships between plants and fungi began at this time and exist today

28. Continental Drift  Continents are not fixed but drift across our planet’s surface on plates of crust that float on a hot underlying mantle  Interactions at plate boundaries  Convergent boundaries (moving together)  Divergent boundaries (moving apart)  Transform boundaries (sliding past one another)  Volcanoes, Earthquakes, mountain building, and subduction occur at plate boundaries

31.  The formation and breakup of the supercontinent Pangaea explain many biogeographical puzzles  Land bridges  Fossils found on 2 continents that can’t swim  Rock formations  Apparent puzzle piece fit of the continents

33. 26.6 Taxonomic systems  Old system was 2 Kingdoms (Plant & Animal)  5 kingdom system  Monera, Protists, Plantae, Fungi, Animalia  3 Domain system has replaced the 5 kingdom system  Archaea, Bacteria, Eukarya