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History of Life On Earth

History of Life On Earth. Today’s OUTLINE:. 1) Geological Time Scale 2) Major Episodes in History of Life 3) Extinctions and Radiations. Geology plays an Important role in Evolutionary Thinking.

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History of Life On Earth

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  1. History of Life On Earth

  2. Today’s OUTLINE: 1) Geological Time Scale 2) Major Episodes in History of Life 3) Extinctions and Radiations

  3. Geology plays an Important role in Evolutionary Thinking Patterns of extinctions and evolutionary change in the fossil record were among the main influences on Darwin’s thinking

  4. Imagine... That all of Earth History is compressed into a single year...

  5. When did life first arise? And in what form? • When did Eukaryotes arise? • What about multicellular organisms (metazoans)? • The invasion of land from the sea? • Mammals? • Humans?

  6. The point of this exercise • Life evolved under anaerobic conditions • Much of the history of Life has been in the forms of prokaryotes and single cell eukaryotes (single cells) • Multicellular organisms are relatively recent • Humans have inhabited this planet for a very very short time

  7. The first life on earth was in the form of prokaryotes • The Oxygen Revolution was a pivotal event that transformed life on Earth • Humans have inhabited this planet for a very very short time

  8. 1.2 bya: First multicellular eukaryotes 535–525 mya: Cambrian explosion (great increase in diversity of animal forms) 500 mya: Colonization of land by fungi, plants and animals 2.1 bya: First eukaryotes (single-celled) 3.5 billion years ago (bya): First prokaryotes (single-celled) 500 1,000 1,500 4,000 3,000 3,500 2,500 2,000 Present Millions of years ago (mya)

  9. Carol Lee, Animal Evolution David Baum, Plant Evolution 1.2 bya: First multicellular eukaryotes 535–525 mya: Cambrian explosion (great increase in diversity of animal forms) Next Lecture 500 mya: Colonization of land by fungi, plants and animals 2.1 bya: First eukaryotes (single-celled) Nicole Perna, Microbial Evolution 3.5 billion years ago (bya): First prokaryotes (single-celled) 500 1,000 1,500 4,000 3,000 3,500 2,500 2,000 Present Millions of years ago (mya)

  10. Another way to look at the Geological Time Scale Cenozoic 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

  11. Formation of Sedimentary rock

  12. Fossils (1) Hard parts mineralized (chemical reactions) (2) Or the bone disintegrates mold filled with dissolved minerals (3) Total preservation: amber, ice, bogs

  13. Radiometric Dating Can tell how old something is by how much radioisotope has disappeared Each isotope has a known half-life, the time required for half the parent isotope to decay

  14. Molecular Clock • Mutations • On average, mutations occur at a given rate Example: Mitochondria: ~2.2%/million years.

  15. Molecular Clock Faster if • Mutation rate is faster if: • Shorter generation time (more meiosis or mitosis per time) • Sloppy polymerase (e.g. HIV) • Inefficient mismatch repair, etc.

  16. Is the fossil record roughly congruent with timing of events based on the molecular clock? Roughly so, but gaps in the fossil record And molecular clock varies among genes and species

  17. Cenozoic • Mesozoic • Paleozoic • Precambrian

  18. Cenozoic Mesozoic Paleozoic Origin of solar system and Earth 4 1 Proterozoic Archaean years ago Billions of 2 3

  19. Boundaries between Eras Marked byExplosive Adaptive Radiations AndMass Extinctions

  20. Mass Extinction Events 800 20 700 600 15 500 400 10 Total extinction rate (families per million years): Number of families: 300 200 5 100 0 0 Mesozoic Paleozoic Cenozoic Era Period E C Tr C O S D P J P N 200 145 65.5 0 542 488 444 416 359 299 251 Time (millions of years ago)

  21. Adaptive Radiations Divergence of a phylogenetic group into forms adapted to various ecological niches. • Happens over short geological time (~5 million years) • Change in environment (Global Climate Change) • Open Niches due to Extinction Or exploitation of new Niche (due to novel trait) • Examples: Response to climate change, Colonization of Land, Air (flight), Cold, High Altitude, colonization of islands

  22. Hawaiian honeycreepers Adaptive Radiations On the islands of Hawaii Hawaiian silverswords

  23. Adaptive radiation often results in a star phylogeny Rapid speciation: Can’t tell which taxa diverged first

  24. 65 mya: Cretaceous Extinction (dinosaurs go extinct) 230 mya: Permian Extinction 570 mya: Cambrian Explosion

  25. Cenozoic: Age of Mammals Mesozoic: Age of Reptiles Paleozoic: Age of Invertebrates Precambrian: Age of Single Cell

  26. ERA: Precambrian “Age of the Single Cell” 90% Earth History Origin of Earth Prokaryotes Oxygen Eukaryotes First animals

  27. ERA: Precambrian “Age of the Single Cell” 90% Earth History Origin of Earth Prokaryotes Oxygen Eukaryotes First animals

  28. The First Single-Celled Organisms The oldest known fossils are stromatolites, rock-like structures composed of many layers of bacteria and sediment • Stromatolites date back 3.5 billion years ago • Prokaryotes were Earth’s sole inhabitants from 3.5 to about 2.1 billion years ago • Will discuss the origins of life (origins of prokaryotes) in next lecture 4 1 years ago Billions of 3 2 Prokaryotes

  29. ERA: Precambrian “Age of the Single Cell” 90% Earth History Origin of Earth Prokaryotes Oxygen Eukaryotes First animals

  30. Oxygen Revolution By about 2.7 billion years ago, O2 began accumulating in the atmosphere and rusting iron-rich terrestrial rocks • “Oxygen revolution” from 2.7 to 2.2 billion yrs ago • O2 in the atmosphere was generated by photosynthetic activity of cyanobacteria (next lecture) • Posed a challenge for life (O2 toxicity) • Provided opportunity to gain energy from light • Allowed organisms to exploit new ecosystems 1 4 years ago Billions of 3 2 Atmospheric oxygen

  31. ERA: Precambrian “Age of the Single Cell” 90% Earth History Origin of Earth Prokaryotes Oxygen Eukaryotes First animals

  32. 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 (talk about this in Next Lecture) • An endosymbiont is a cell that lives within a host cell 1 4 years ago Billions of 3 2 Single-celled eukaryotes

  33. The Origin of Multicellularity • Comparisons of DNA sequences date the common ancestor of multicellular eukaryotes to 1.5 billion years ago • Oldest known fossils of multicellular eukaryotes are of small algae that lived about 1.2 billion years ago 1 4 years ago Billions of • First major diversification of multicellular eukaryotes corresponds to a time of the thawing of the planet (starting 565 million years ago) • Another major diversification happened 30 million years later (Cambrian Explosion) 3 2 Multicellular eukaryotes

  34. (1) Precambrian-Paleozoic Boundary(~570 MYA) Fossil Deposits: Doushanto fossils Ediacaran fossils Burgess Shale Cambrian Explosion

  35. Calymeme celebra (1) Precambrian-Paleozoic Boundary (~570 MYA) Cambrian Explosion Radiations: Evolution of hard body parts Diversification of body forms Radiation of Invertebrates Extinctions???? Hard to tell, Precambrian species were single cell, soft

  36. Fig 25-UN6 Animals 1 4 Billions of yearsago 3 2

  37. The Cambrian Explosion • The Cambrian explosion originally referred to the sudden appearance of fossils resembling modern phyla in the Cambrian period (~543 to 525 million years ago)—mostly based on the Burgess Shale fossils • Phylogenetic analysis suggest that many animal phyla diverged before the Cambrian explosion recorded in the fossil record, perhaps as early as 700 million to 1 billion years ago

  38. Annelida Agnatha Mollusca Arthropoda Million Years Ago Gnathostomata Echinodermata 0 200 Cambrian “Cambrian Explosion” 600 Based on phylogeny of animals based on DNA sequence data, the radiation of animals predates the geological record of the Cambrian Explosion 800 1000 Precambrian 1200 Wray et al. 1996 1400

  39. Fossil Record vs Molecular Clock • Molecular clock and fossil record are not always congruent • Fossil record is incomplete, and soft bodied species are usually not preserved • Mutation rates can vary among species (depending on generation time, replication error, mismatch repair) • But they provide complementary information • Fossil record contains extinct species, while molecular data is based on extant taxa • Major events in fossil record could be used to calibrate the molecular clock

  40. Cambrian Explosion

  41. Cambrian Explosion --> Origins of Animals: I will discuss the genetic mechanisms of this Adaptive Radiation in the lecture on Animal Diversity

  42. The CambrianExplosion: Major Fossil Formations Doushantuo Formation (Southern China): 570 million years agoEdiacaran Fauna (Australia): 565-544 million years agoThe Burgess Shale (British Columbia, Canada): 525-515 million yrs ago

  43. Doushantuo formation Southern China • 570 million years ago • Clusters of cells (embryos?) • Sponges Fossilized metazoan embryo at the 256 cell stage

  44. The Cambrian Explosion • The Doushantuo fossils in China provide evidence of modern animal phyla tens of millions of years before the Cambrian explosion recorded in the Burgess Shale (~570 million years ago) The Chinese fossils, along with DNA data, suggest that the Cambrian explosion occurred over a more extended period of time than previously thought (a) Two-cell stage (b) Later stage 200 µm 150 µm

  45. Ediacaran Fauna Dickinsonia Tribrachidium heraldicum Ediacaran Hills, Australia

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