Chapter 25

1. Chapter 25 The History of Life on Earth

2. What you need to know… • The age of the Earth and when prokaryotic and eukaryotic life emerged. • Characteristics of the early planet and its atmosphere. • How Miller and Urey tested the Oparin-Haldane hypothesis and what they learned. • Methods used to date fossils and rocks. • Evidence for endsymbiosis. • How continental drift can explain the current distribution of species.

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

4. Fig 25-UN1 Cryolophosaurus

5. Concept 25.1: Conditions on early Earth made the origin of life possible • Chemical and physical processes on early Earth may have produced very simple cells through a sequence of 4 stages: 1. Small organic molecules were synthesized 2. Joining of these small molecules into macromolecules (proteins, carbs, etc) 3. Packaging of molecules into “protobionts” (membrane-containing droplets, whose internal chemistry differed from that of the external environment) 4. Origin of self-replicating molecules

6. Synthesis of Organic Compounds on Early Earth • Earth formed about 4.6 billion years ago, along with the rest of the solar system • Life on Earth ~ 3.8-3.9 billion years ago • Earth’s early atmosphere likely contained water vapor and chemicals released by volcanic eruptions (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen, hydrogen sulfide)

7. A. I. Oparin and J. B. S. Haldane – hypothesized that the early atmosphere, thick with water vapor, nitrogen, carbon dioxide, methane, ammonia, hydrogen, and hydrogen sulfide, with energy from lightening and UV radiation could have formed organic compounds • Stanley Miller and Harold Urey conducted lab experiments to test this hypothesis and produced a variety of amino acids

8. evidence is not yet convincing that the early atmosphere was in fact reducing • Instead of forming in the atmosphere, the first organic compounds may have been synthesized near submerged volcanoes and deep-sea vents Video: Tubeworms Video: Hydrothermal Vent

9. Abiotic Synthesis of Macromolecules • Amino acids have also been found in meteorites • Small organic molecules polymerize when they are concentrated on hot sand, clay, or rock

10. Protobionts • Replication and metabolism are key properties of life • Protobionts are aggregates of abiotically produced molecules surrounded by a membrane or membrane-like structure • Protobionts exhibit simple reproduction and metabolism and maintain an internal chemical environment

11. Experiments demonstrate that protobionts could have formed spontaneously from abiotically produced organic compounds • For example, small membrane-bounded droplets called liposomes can form when lipids or other organic molecules are added to water

12. Fig. 25-3 20 µm Glucose-phosphate Glucose-phosphate Phosphatase Starch Amylase Phosphate Maltose (a) Simple reproduction by liposomes Maltose (b) Simple metabolism

13. Self-Replicating RNA and the Dawn of Natural Selection • The first genetic material was probably self-replicating 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

14. Concept 25.2: The fossil record documents the history of life • The fossil record reveals changes in the history of life on earth • Sedimentary rocks are deposited into layers called strata and are the richest source of fossils Video: Grand Canyon

15. Fig. 25-4 Rhomaleosaurus victor, a plesiosaur Present Dimetrodon 100 million years ago Casts of ammonites 175 200 270 300 Hallucigenia 4.5 cm 375 Coccosteus cuspidatus 400 1 cm Dickinsonia costata 500 525 2.5 cm 565 Stromatolites Tappania, a unicellular eukaryote 600 3,500 1,500 Fossilized stromatolite

16. Fig. 25-4-1 Hallucigenia 1 cm Dickinsonia costata 500 525 2.5 cm 4.5 cm 565 Stromatolites Tappania, a unicellular eukaryote 600 3,500 1,500 Fossilized stromatolite

17. Few individuals have fossilized, and even fewer have been discovered • The fossil record is biased in favor of species that • Existed for a long time • Were abundant and widespread • Had hard parts Animation: The Geologic Record

18. How Rocks and Fossils Are Dated • 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

19. 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)

20. Radiocarbon dating 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 provide dating information • Reversals of the magnetic poles leave their record on rocks throughout the world

21. The Origin of New Groups of Organisms • Mammals belong to the group of animals called tetrapods • The evolution of unique mammalian features through gradual modifications can be traced from ancestral synapsids through the present

22. Fig. 25-6 Synapsid (300 mya) Temporal fenestra Key Articular Dentary Quadrate Squamosal Therapsid (280 mya) Reptiles (including dinosaurs and birds) Temporal fenestra EARLY TETRAPODS Dimetrodon Early cynodont (260 mya) Synapsids Very late cynodonts Temporal fenestra Earlier cynodonts Therapsids Later cynodont (220 mya) Mammals Very late cynodont (195 mya)

23. Concept 25.3: Key events in life’s history include the origins of single-celled and multicelled organisms and the colonization of land • The geologic record is divided into the Archaean, the Proterozoic, and the Phanerozoic eons

24. Table 25-1

25. The Phanerozoic encompasses multicellular eukaryotic life • The Phanerozoic is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic • Major boundaries between geological divisions correspond to extinction events in the fossil record

26. Fig. 25-7 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

27. 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

28. Fig 25-UN2 1 4 Billions of years ago 2 3 Prokaryotes

29. Photosynthesis and the Oxygen Revolution • Most atmospheric oxygen (O2) is of biological origin • O2 produced by oxygenic photosynthesis reacted with dissolved iron and precipitated out to form banded iron formations • The source of O2 was likely bacteria similar to modern cyanobacteria

30. By about 2.7 billion years ago, O2 began accumulating in the atmosphere and rusting iron-rich terrestrial rocks • This “oxygen revolution” from 2.7 to 2.2 billion years ago • Posed a challenge for life • Provided opportunity to gain energy from light • Allowed organisms to exploit new ecosystems

31. Fig 25-UN3 1 4 Billions of years ago 2 3 Atmospheric oxygen

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 • An endosymbiont is a cell that lives within a host cell

33. Fig 25-UN4 1 4 Billions of years ago 3 2 Single- celled eukaryotes

34. Fig. 25-9-1 Cytoplasm Plasma membrane DNA Ancestral prokaryote Endoplasmic reticulum Nucleus Nuclear envelope

35. Fig. 25-9-2 Aerobic heterotrophic prokaryote Mitochondrion Ancestral heterotrophic eukaryote

36. Fig. 25-9-3 Photosynthetic prokaryote Mitochondrion Plastid Ancestral photosynthetic eukaryote

37. Key evidence supporting an endosymbiotic origin of mitochondria and plastids: • Similarities in inner membrane structures and functions • Division is similar in these organelles and some prokaryotes • These organelles transcribe and translate their own DNA • Their ribosomes are more similar to prokaryotic than eukaryotic ribosomes

38. The Origin of Multicellularity • The evolution of eukaryotic cells allowed for a greater range of unicellular forms • Multicellular eukaryotes – evolved ~1.2 billion years ago • A second wave of diversification occurred when multicellularity evolved and gave rise to algae, plants, fungi, and animals

39. 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

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

41. Concept 25.4: The rise and fall of dominant groups reflect continental drift, mass extinctions, and adaptive radiations • The history of life on Earth has seen the rise and fall of many groups of organisms Video: Volcanic Eruption Video: Lava Flow

42. 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

43. 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

44. 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

45. Fig. 25-13 Present Cenozoic Eurasia North America Africa 65.5 India South America Madagascar Australia Antarctica Laurasia 135 Mesozoic Gondwana Millions of years ago Pangaea 251 Paleozoic

46. 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

47. 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 (loss of large numbers of species in short periods of time) • By removing large numbers of species, ecological communities can be drastically altered losing evolutionary lineages forever • EX. Dinosaurs 65 mya

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

49. Fig. 25-14 800 20 700 600 15 500 Number of families: 400 Total extinction rate (families per million years): 10 300 200 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)

50. Fig. 25-15 NORTH AMERICA Chicxulub crater Yucatán Peninsula