Chapters 25 and 26

1. Chapters 25 and 26 • Assignment 2 February 8th • Test 2 February 10th • Essay 1 February 15th

3. Lost Worlds • Past organisms were very different from those now alive • The fossil record shows macroevolutionary changes over large time scales including • The origin of photosynthesis • The emergence of terrestrial vertebrates • Long-term impacts of mass extinctions

4. How did life on earth get its start? • Processes on early Earth may have produced very simple cells through a sequence of stages: 1. Abiotic synthesis of small organic molecules 2. Joining of these small molecules into macromolecules 3. Packaging of molecules into “protobionts” 4. Origin of self-replicating molecules

5. Synthesis of Organic Compounds on Early Earth • Evidence indicates that earth formed about 4.6 billion (with a ‘b’) years ago, along with the rest of the solar system • Earth’s early atmosphere likely contained water vapor and chemicals released by volcanic eruptions (nitrogen, nitrogen oxides (NOx’s), carbon dioxide, methane, ammonia, hydrogen, hydrogen sulfide). • No oxygen gas! H2S CH4 NH4 NOx

6. How did life on earth get its start? • Stanley Miller and Harold Urey conducted lab experiments that showed abiotic synthesis of organic molecules is possible • Amino acids have also been found in meteorites • Small organic molecules polymerize when they are concentrated on hot sand, clay, or rock

7. Protobionts? • Reproduction and metabolism are key properties of life • Protobionts are collections of abiotically produced molecules, surrounded by a membrane or membrane-like structure • They would show simple reproduction and metabolism, and maintain an internal chemical environment (beginnings of homeostasis)

8. Experiments demonstrate that protobionts could have formed spontaneously from those abiotically produced organic compounds • For example, small membrane-bounded droplets called liposomes can form when lipids or other organic molecules are added to water If you add these two enzymes to a liposome in a lab, you can get simple metabolism

9. Self-Replicating RNA and the Dawn of Natural Selection • The first genetic material was probably RNA, not DNA • RNA molecules called ribozymes have been found to catalyze many different reactions • For example, ribozymes can make complementary copies of short stretches of their own sequence, or other short pieces of RNA Ribozyme

10. Early protobionts with self-replicating, catalytic RNA would have been more effective at using resources and would have increased in number through natural selection • The early genetic material might have formed an “RNA world” + = life (?)

11. Fossilized stromatolite

12. What proportion of dead organisms fossilized? • Not many! • Which ones WOULD fossilize? • Organisms that existed for a longtime • Organisms that were abundant and widespread • Organisms that had hardparts

13. How Do We Know How Old Rocks and Fossils Are? • Sedimentary strata reveal the relative ages of fossils • The absolute ages of fossils can be determined by radiometric dating • A “parent” isotope decays to a “daughter” isotope at a constant rate • Each isotope has a known half-life, the time required for half the parent isotope to decay

14. Fig. 25-5 Accumulating “daughter” isotope Fraction of parent isotope remaining 1/2 Remaining “parent” isotope 1/4 1/8 1/16 4 3 2 1 Time (half-lives)

15. How Rocks and Fossils Are Dated • Carbon dating (half life of 5,730 years) can be used to date fossils up to 75,000 years old • For older fossils, some isotopes can be used to date sedimentary rock layers above and below the fossil • The magnetism of rocks can also provide dating information • Reversals of the magnetic poles leave their record on rocks throughout the world

17. You discover three fossil organisms and want to determine their dates. You measure the percentage of carbon-14 (half-live = 5,730 years) remaining in the fossils. Place them in order from oldest to youngest. • A, B, C • B, C, A • C, A, B • A, C, B

18. Ceno- zoic Meso- zoic Humans Paleozoic Colonization of land Animals Origin of solar system and Earth 4 1 Proterozoic Archaean Prokaryotes years ago Billions of 3 2 Multicellular eukaryotes Single-celled eukaryotes Atmospheric oxygen

19. Living Stromatolites

20. The First Living Organisms • The oldest known fossils are stromatolites, rock-like structures made of many layers of photosynthesizing bacteria and sediment • Stromatolites date back 3.5 billion years ago • Prokaryotes were Earth’s only living residents from 3.5 to about 2.1 billion years ago

21. Photosynthesis and the Oxygen Revolution • Most atmospheric oxygen (O2) is of biological origin, from this photosynthesis. • The source of O2 was likely bacteria similar to modern cyanobacteria

22. The First Eukaryotes • The oldest fossils of eukaryotic cells date back 2.1 billion years • The hypothesis of endosymbiosis proposes that mitochondria and plastids (chloroplasts and related organelles) were formerly small prokaryotes living within larger host cells

23. Fig. 25-9-4 Cytoplasm Plasma membrane DNA Ancestral prokaryote Endoplasmic reticulum Nucleus Nuclear envelope Aerobic heterotrophic prokaryote Photosynthetic prokaryote Mitochondrion Mitochondrion Ancestral heterotrophic eukaryote Plastid Ancestral photosynthetic eukaryote

24. Fig 25-UN5 1 4 Billions of years ago 2 3 Multicellular eukaryotes

25. The Cambrian Explosion • The Cambrian explosion refers to the sudden appearance of fossils resembling modern phyla in the Cambrian period (535 to 525 million years ago) • The Cambrian explosion provides the first evidence of predator-prey interactions

26. Fig 25-UN6 Animals 1 4 Billions of years ago 3 2

27. Fig. 25-11 (a) Two-cell stage (b) Later stage 200 µm 150 µm

28. The Colonization of Land • Fungi, plants, and animals began to colonize land about 500 million years ago • Plants and fungi likely colonized land together by 420 million years ago • Arthropods and tetrapods are the most widespread and diverse land animals • Tetrapods evolved from lobe-finned fishes around 365 million years ago

29. Fig 25-UN7 Colonization of land 1 4 Billions of years ago 3 2

30. Continental Drift At three points in time, the land masses of Earth have formed a supercontinent: 1.1 billion, 600 million, and 250 million years ago Earth’s continents move slowly over the underlying hot mantle through the process of continental drift Oceanic and continental plates can collide, separate, or slide past each other Interactions between plates cause the formation of mountains and islands, and earthquakes

31. Fig. 25-12 North American Plate Eurasian Plate Crust Caribbean Plate Philippine Plate Juan de Fuca Plate Arabian Plate Indian Plate Cocos Plate Mantle South American Plate Pacific Plate Nazca Plate African Plate Outer core Australian Plate Inner core Antarctic Plate Scotia Plate (b) Major continental plates (a) Cutaway view of Earth

32. Consequences of Continental Drift Formation of the supercontinent Pangaea about 250 million years ago had many effects • A reduction in shallow water habitat • A colder and drier climate inland • Changes in climate as continents moved toward and away from the poles • Changes in ocean circulation patterns leading to global cooling

33. Consequences of Continental Drift The break-up of Pangaea lead to allopatric speciation The current distribution of fossils reflects the movement of continental drift For example, the similarity of fossils in parts of South America and Africa is consistent with the idea that these continents were formerly attached

35. Mass Extinctions • The fossil record shows that most species that have ever lived are now extinct • At times, the rate of extinction has increased dramatically and caused a mass extinction

36. The “Big Five” Mass Extinction Events • In each of the five mass extinction events, more than 50% of Earth’s species became extinct