The Fossil Record and Earth's Early History: Key Concepts and Evidence

1. CHAPTER 17 THE HISTORY OF LIFE

3. SECTION 1 THE FOSSIL RECORD

4. KEY CONCEPT QUESTIONS: • What is the fossil record? • What information do relative dating and radioactive dating provide about fossils? • What are the main divisions of the geologic time scale?

5. PALEONTOLOGISTS • scientists who study fossils • they infer what past life forms were like • they also classify organisms

6. FOSSIL RECORD • information about past life, including the structure of organisms, what they ate, what ate them, in what environment they lived, and the order in which they lived • shows how different groups of organisms have changed over time • Fossils occur in a particular order • certain fossils appear only in older rockss

7. Fossil record • Today’s organisms descended from ancestral species

8. Specific environmental conditions are necessary in order for fossils to form.

9. Fossils can form in several ways. • Permineralization occurs when minerals carried by water are deposited around a hard structure.

10. A natural cast forms when flowing water removes all of the original tissue, leaving an impression.

11. Trace fossils record the activity of an organism.

12. Amber-preserved fossils are organisms that become trapped in tree resin that hardens after the tree is buried.

13. Preserved remains form when an entire organism becomes encased in material such as ice.

14. Only a tiny percentage of living things became fossils. • Specific conditions are needed for fossilization.

15. Interpreting Fossil Evidence • Natural forces reveal fossils • Fossil reconstruction • RELATIVE DATING • age of a fossil is determined by comparing its placement with that of fossils in other layers of rock – older layers of rock are closer to Earth’s core

16. Index fossils are another tool to determine the age of rock layers. • Index fossils can provide the relative age of a rock layer. • existed only during specific spans of time • occurred in large geographic areas • Index fossils include fusulinids and trilobites.

17. protrons neutrons • Radiometric dating uses decay of unstable isotopes. • Isotopes are atoms of an element that differ in their number of neutrons.

18. Isotopes are atoms of an element that differ in their number of neutrons. • A half-life is the amount of time it takes for half of the isotope to decay.

20. GEOLOGIC TIME SCALE • scale used by paleontologists to represent evolutionary time • Scientists think the Earth is about 6billion years old. • Geologic time begins with the Precambrian period – 544-650 million years ago

21. consist of two or more periods • three eras: Cenozoic, Mesozoic, Paleozoic • Eras last tens to hundreds of millions of years.

22. most commonly used units of time on time scale • associated with rock systems. • Periods last tens of millions of years. • Epochs last several million years.

23. To view video you should have the powerpoint in “slideshow” format • McDougall video – Geologic time (ch. 12)

24. KEY CONCEPT QUESTIONS: • What is the fossil record? • information about past life, including the structure of organisms, what they ate, what ate them, in what environment they lived, and the order in which they lived • What information do relative dating and radioactive dating provide about fossils? • Relative dating - age of a fossil is determined by comparing its placement with that of fossils in other layers of rock • the use of half-lives to determine the age of a sample • What are the main divisions of the geologic time scale? • Eras and periods

25. SECTION 2 EARTH’S EARLY HISTORY “…sparked by just the right combination of physical events & chemical processes…”

26. KEY CONCEPT QUESTIONS: • What substances made up the earth’s early atmosphere? • What did Miller and Urey’s experiments show? • What occurred when oxygen was added to Earth’s atmosphere? • What hypothesis explains the origin of eukaryotic cells?

27. We know spontaneous generation was disproved. • If life only comes from life, then how did life on Earth first begin?

28. The historical tree of life can be documented with evidence. The Origin of Life on Earth is another story…

29. Earth was very different billions of years ago. • There have been many hypotheses of Earth’s origins. • The most widely accepted hypothesis of Earth’s origins is the nebula hypothesis (aka: The Big Bang).

30. Formation of the Earth • Geologic evidence shows that Earth was not “born” in a single event. • Instead, pieces of cosmic debris were probably attracted to one another over the course of about 100 million years. • While the planet was young, it was struck by one or more objects, possibly as large as the planet Mars. This collision produced enough heat to melt the entire globe.

31. Once Earth melted, its elements rearranged themselves according to density – more dense toward the core, less dense near the surface • sky was not blue but pinkish-orange • Earth’s early atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water

32. About 4 billion years ago, Earth cooled enough to allow the first solid rocks to form on its surface. • For millions of years afterward, violent volcanic activity shook Earth’s crust. • Comets and asteroids bombarded its surface. • Oceans did not exist because the surface was extremely hot

33. About 3.8 billion years ago, Earth’s surface cooled enough for water to remain a liquid. • Thunderstorms drenched the planet, and oceans covered much of the surface. • Those primitive oceans were brown because they contained lots of dissolved iron. • The earliest sedimentary rocks, which were deposited in water, have been dated to this period. • This was the Earth on which life appeared • 200 to 300 million years after Earth cooled enough to carry liquid water, cells similar to modern bacteria were common – where did they come from?

34. electrodes “atmosphere” water “ocean” heat source amino acids Several sets of hypotheses propose how life began on Earth. • There are two organic molecule hypotheses. • Miller-Urey experiment • meteorite hypothesis

35. Conditions on early Earth • water vapor (H2O), CO2, N2, NOx, H2,NH3, CH4, H2S • lots of available H & its electron • no free oxygen • Energy source • lightning, UV radiation, volcanic low O2 = organic molecules do not breakdown as quickly What’s missingfrom thatatmosphere?

36. First Organic Molecules • organic compounds • carbohydrates, proteins, lipids, nucleic acids • 1950’s Miller and Urey tried to simulate Earth’s early atmosphere to see if they could find out how organic compounds were formed • Miller and Urey's experiments suggested how mixtures of the organic compounds necessary for life could have arisen from simpler compounds present on a primitive Earth. • similar experiments based on more current knowledge of Earth’s early atmosphere have also produced organic compounds

37. Stanley Miller University of Chicago • Yieldedamino acids • hydrocarbons • N bases • other organic molecules

38. Evolution of DNA and RNA • One hypothesis suggests that RNA could have evolved before DNA – RNA is more simple because it is single stranded

39. Ribozymes are RNA molecules that catalyze their own replication. • DNA needs enzymes to replicate itself. • A hypothesis proposes that RNA was the first genetic material.

40. Key Events in Origin of Life • Key events in evolutionary history of life on Earth • life originated 3.5–4.0 bya

41. Free Oxygen • MICROFOSSILS • microscopic fossils of single-celled prokaryotic organisms that resemble modern bacteria have been found in rocks more than 3.5 billion years old • Early Earth had no free oxygen

42. Microbes have changed the physical and chemical composition of Earth. • The oldest known fossils are a group of marine cyanobacteria. • prokaryotic cells • added oxygen toatmosphere • deposited minerals

43. Fossil stromatolites provide evidence of early colonies of life.

44. What type of metabolic process would have come first to put oxygen into the atmosphere? • Photosynthetic bacteria became common in the shallow seas of the Precambrian • The rise of oxygen in the atmosphere drove some life forms to extinction, while other life forms evolved new, more efficient metabolic pathways that used oxygen for respiration

45. Origin of Eukaryotic cells • About 2billion years ago, prokaryotic cells – cells without nuclei – began evolving internal cell membranes • other prokaryotic organisms began to enter this ancestral eukaryotic cell • ENDOSYMBITOTIC THEORY • proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms

46. Eukaryotic cells may have evolved through endosymbiosis. • Endosymbiosis is a relationship in which one organism lives within the body of another. • Mitochondria and chloroplasts may have developed through endosymbiosis.

47. Sexual reproduction and multicellularity • evolution of increasingly complex multicellular organisms began about 1 billion years ago • sexual reproduction shuffles genes in each generation • increase in genetic variation greatly increases the chances of evolutionary change in a species due to natural selection

48. KEY CONCEPT QUESTIONS: • What substances made up the earth’s early atmosphere? • water vapor (H2O), CO2, N2, NOx, H2,NH3, CH4, H2S • What did Miller and Urey’s experiments show? • Yielded amino acids, hydrocarbons, N bases, other organic molecules • What occurred when oxygen was added to Earth’s atmosphere? • drove some life forms to extinction, while other life forms evolved new, more efficient metabolic pathways that used oxygen for respiration • What hypothesis explains the origin of eukaryotic cells? • Endosymbiotic theory

49. SECTION 3 EVOLUTION OF MULTICELLULAR LIFE

50. KEY CONCEPT QUESTIONS: • What were the characteristic forms of life in the Paleozoic, mesozoic, and Cenozoic eras?