The History of Life

1. The History of Life

2. Fossils and Ancient Life • The fossil record provides evidence about the history of life on Earth. • It shows how different groups of organisms, including species, have changed over time.

3. Fossil Formation • Water carries small rock particles to lakes and seas. • Dead organisms are buried by layers of sediment, which forms new rock • Preserved remains may be discovered and analyzed

4. Paleontology • Paleontologists occasionally unearth the remains of an entire organism • Usually they must reconstruct an extinc species from a few fossil bits. • Paleontologists look for anatomical similarities--and differences– between the fossil and living organisms • Age is EXTREMELY important

5. Relative Dating • The age of a fossil is determined by comparing its placement with that of fossils in other layers of rock • Sedimentary rock layers form through gradual deposition of layers of sand, rock, and sediment • Rock layers form in order by age—oldest on the bottom

6. Index Fossils • Used to compare the relative ages of fossils. • To be used, a species must be easily recognized, and have existed for a short period over a wide geographic range Trilobites, common ancestors of the horseshoe crab are often used as index fossils

7. Distant Relatives

8. Index Fossils Relative dating allows paleontologists to estimate a fossil’s age compared with that of other fossils

9. Radioactive Dating • Scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains • A half-life is the length of time required for half of the radioactive atoms in a sample to decay • Carbon-14 has a half-life of 5730 years • Carbon-12 does not decay and can be used for a comparison

10. Radioactive Dating Because of its half-life, C-14 is useful only for dating fossils younger than about 60,000 years.

11. Pre-Ancient History of Earth Once upon a time… • Geologic evidence shows that Earth, which is about 4.6 billion years old, was not “born” in a single event. • Pieces of cosmic debris were probably attracted to one another over the course of 100 million years.

12. Formation of Earth

13. Formation of Earth • While young, Earth was probably struck by an object, possibly as large as Mars. • The collision created enough heat to melt the entire globe.

14. Once melted, the elements rearranged themselves according to density. More dense elements formed the planet’s core. Radioactive decay creates enough heat to keep the core liquid. Formation of Earth

15. Less dense elements floated to the surface like fat on chicken soup. These elements cooled to form a solid crust. The least dense elements (gasses) formed the air. Formation of Earth

16. Earth’s early atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide and water…deadly. Formation of Earth

17. About 4 billion years ago, Earth cooled enough to allow the first solid rocks to form on its surface. 3.8mya, the surface cooled enough for water to remain liquid. Primitive oceans were brown, containing lots of iron. Thunderstorms drenched the planet, and the brown oceans covered most of the surface. This is the world in which life began. Formation of Earth

18. Early Organics • Atoms do not assemble themselves into complex organic molecules or living cells on Earth today. • Oxygen would react with the formations and destroy them • Organisms today would eat newly appearing molecules

19. Early Organics • The atmosphere and environment of early earth was very different than Earth today. • Oxygen was hardly present in the environment and not available to interact and interfere with infantile organic molecules during their formation.

20. Miller and Urey • American chemists tried to reproduce the action on earth prior to oxygen to see if molecules would develop • They filled a flask with hydrogen, methane, ammonia, and water. • Electric sparks passed through the mixture to simulate lightning.

21. Early Organics Spark Gas mixture Water vapor Amino acids

22. Early Organics • The results were spectacular! • In a few days several amino acids—the building blocks of proteins—began to accumulate • We now know that Miller and Urey’s mixture was actually not accurate • Using accurate gasses a repeat of the experiment in 1995 produced cytosine and uracil, two of the bases found in nucleic acids

23. The Puzzle of Life’s Origin • Organic molecular stew is great, but it is not a cell • 200-300 million years after standing water appeared on earth bacteria were everywhere, but where did they come from?

24. Life’s Origin • Under certain conditions large organic molecules can form protenoid microspheres • Selectively permeable, they have many characteristics of cells, though are still not alive

25. Puzzle of Life • Under the right conditions, some RNA sequences can help DNA replicate • Others process mRNA • Some catalyze reactions • Some even grow and replicate themselves • Where the DNA and RNA relationship evolved has yet to be discovered.

26. Free Oxygen • Fossil evidence sows photosynthetic bacteria were common in the Precambrian seas • 2.2 bya these organisms were churning out oxygen from photosynthesis

27. Rusting Ocean • The Oxygen reacted with the iron in the water and formed iron oxide • The rust fell out of solution and lined the ocean floor

28. Free Oxygen • Atmospheric Oxygen rose • Methane and Hydrogen sulfide decreased • Ozone layer began to form • Sky turned it’s now-familiar shade of blue • Biologists relate this to the first pollution crisis—to these early cells, oxygen was poison.

29. Free Oxygen • The gradual rise of oxygen in the atmosphere drove some life forms to extinction • Others adapted and evolved new, more efficient metabolic pathways to use oxygen for respiration • Some organisms were forced to retreat to airless habitats, where they survive today.

30. Endosymbiotic Theory

31. Endosymbiotic Theory • Mitochondrial and Chloroplast membrane structure is similar to prokaryotic membranes • DNA similar to bacterial DNA • Have own ribosomes with size and structure of bacterial ribosomes • Reproduce by binary fission when greater cell divides

33. Sexual Reproduction • Asexual reproduction restricts genetic variation to mutations in DNA • Sexual reproduction shuffles and reshuffles genes in each generation • By increasing variation in all gene combinations, probability of favorable combinations (adaptation) occurring is increased

34. Multicellularity • Few hundred million years after evolution of sexual reproduction • First multicellular organisms experienced great increases in diversity • Found many unfilled niches and with that, evolutionary success Jellyfish--primitive multicellularity

35. Onto the LAND! • During the Devonian Period, land was becoming more expansive and the first aquatic animals began to move onto the land. • Insects (arthropods) were making good use of drier habitat so there was an untapped food source waiting to be had if predators could only survive on the dry land.

36. Onto the LAND!! Sarcopterygii-extant species of fleshy-finned fish

37. Onto the LAND Lungfish can breathe air for short trips between sources of water. Some have one small lung in addition to gills. Mudskipper-amphibious fish

38. Patterns of Evolution Six Topics of Macroevolution • Extinction • Adaptive radiation • Convergent evolution • Coevolution • Changes in Developmental Genes

39. Extinction • Over 99% of all species that ever lived are now extinct • Survival of the fittest causes exclusion and extinction • Several episodes of mass extinctions have wiped out entire ecosystems Complete Triceratops skeleton auctioned in Paris

40. Extinction • During mass extinctions food webs collapse • Disrupted energy flow through the biosphere can destabilize otherwise fit organisms • Many species become extinct for reasons not directly related to ordinary natural selection but as a response to catastrophic environmental change.

41. Extinction • One hypothesis suggests that at the end of the Cretacious the impact of an asteroid wiped out the dinosaurs • An asteroid did strike earth at that time, though the effect is unproven.

42. Extinction • The trend has been to look for a single major cause for each mass extinction. • Today is is more accepted that mass extinctions result from several factors. • Many large volcanoes were erupting, continents were moving, sea levels were changing • Specifics are hard to come-by and causes even more elusive

43. Extinction • Leaves habitats open for surviving species • Results in a burst of evolution that produces many new species • Extinction of dinosaurs cleared the way for mammals and birds

44. Adaptive Radiation • Single species, or small group of species, has evolved, through natural selection and other processes, into diverse forms that live in different ways Honeycreepers

45. Anolis lizards Adaptive Radiation

46. Adaptive Radiation • Can occur on much larger scale • Dinosaurs experienced adaptive radiation and “ruled” Earth for 150 million years • The group of species (dinosaurs) that underwent adaptive radiation dominated • Mammals that evolved about the same time lived in the shadow of widely specialized and adapted dinosaurs.

47. Adaptive Radiation • Disappearance of the dinosaurs cleared the way for mammal radiation • Adaptive radiation of mammals produced the great diversity of mammals from the Cenozoic period. Smilodon fatalis -distant member of the cat family

48. Adaptive Radiation Elephas falconeri Dwarf Mammoth Dicerorhinus Canis lupus AMERICAN LION  panthera leo atrox Arctodus simus Giant Beaver

49. Adaptive Radiation

50. Convergent Evolution • Development of the same morphological trait in unrelated lineages • The same thing shows up at different times or in different places in different organisms • Similar environmental pressures can cause similar adaptations to arise independently, all arriving at the same solution to the problem