Chapter 19: History of Life on Earth

1. Chapter 19: History of Life on Earth

2. Section 1: How did Life Begin? • The condition of early Earth were hypothesized to have oceans filled with small organic molecules by an activation of solar radiation, volcanic eruptions and lightning • As hypothesized by Aleksandr Oparin and John B. S. Haldane in the 1920’s

3. Miller-Urey Experiment • Stanley Miller and Harold Urey hypothesized that the early atmosphere contained hydrogen-containing gases such as water vapor, methane, and ammonia • Both hypotheses were assimiliated in a closed system by Miller and Urey

4. Miller-Urey Experiment • http://evolutionoftruth.com/evo/millerurey.htm

5. Miller-Urey Experiment • Miller-Urey Experiment clip • Gases combined: Methane, Hydrogen gas, Ammonia, Water Vapor • Products: Amino acids, fatty acids, and other hydrocarbons • As a result, the experiment showed that under certain conditions, organic compounds could form from inorganic molecules

6. Recent Discoveries • With a lack of an ozone layer, the ammonia and methane would have been destroyed by the ultraviolet radiation, but without these gases, the experiment would not work • Among the hypotheses that address the origin of life, one states that early biological molecules formed close to hydrothermal vents. Organic molecules may also arrived on early Earth in meteorites.

7. Hydrothermal Vents • The chemical reactions needed to produce the first biological molecules happened in the ocean where hydrothermal vents provided the energy and the protected the molecules from the sun’s UV radiation

8. Space • Some meteorites from space contain some biological molecules such as amino acids. • Perhaps organic molecules arrived from outer space meteorites. It is known that meteorite showers were more frequent during early Earth than now.

9. Microspheres leading to cellular organization • Lipids (like oil) can gather into vesicles or spheres called microspheres • First step to cell organization, however not a life from without the ability of reproducing or passing down information

10. Origin of heredity • First proposed genetic material: RNA • hypothesized by Thomas Cech and Sidney Altman because: • RNA can be formed spontaneously in water • RNA acts as catalysts to make protein, this RNA molecule is called a ribozyme • RNA is self-replicating

12. Section 19.2 The Age of Earth • The age of Earth is about 4.5 billion years old • The fossil record includes all fossil remains of living things on Earth • Fossils are physical evidences of a deceased organism • They can appear in a number of different objects such as rocks, amber and ice.

13. Fossils

14. How do fossils form? • Most fossils are found in sedimentary rock and form when fine sediment buries organisms • The sediment can be moved by wind, water, or volcanic eruptions • Areas with wet lowlands or slow-moving bodies of water are excellent for fossil formation • However, if an organism’s body isn’t buried, it may simply decay before fossilizing

16. How do fossils form? Cont. • Over time, sedimentary rock forms layers, strata, with the youngest layer being on top, but due to geologic events such as earthquakes, sometimes strata can shift • Scientists use two different types of dating methods to find the age of fossils

18. Relative Dating • Estimating the age of fossils with respect to another rock or fossil • An index fossil (fossil of an organism that was common and had widespread geographical distribution during a certain time in history) can estimate the time period of another fossil found around the index fossil • This method is not very accurate and only an estimation

19. Radiometric Dating • This method can determine the actual age of a fossil in years • Radioisotopes (radioactive parent) break down into more stable forms (stable daughter) • Half life—the amount of time it takes for ½ of the radioisotope to decay

20. At the end of the first half-life, ½ of the parent is left • At the end of the second half-life, ¼ of the parent is left

21. Examples of different radioactive isotopes

22. With the help of fossils, scientists have been able to put together a chronology of Earth’s history—The Geologic Time Scale • Starts with Precambrian time then the Paleozoic, Mesozoic, and Cenozoic Eras respectively

25. Section 19-3 Evolution of Life 1. The Precambrian time spanned between 4.5 billion and 542 million years ago. 2. During this time, Early Earth was a dangerous place. Meteors bombarded the planet in large numbers making the environment hostile and hot.

26. 3. The most common fossil found from the Precambrian time was cyanobacteria, which are photosynthetic prokaryotes. Stromatolites, layers/mats of cyanobacteria

27. 4. The early Earth’s atmosphere lacked oxygen. Cyanobacteria began adding oxygen to the air by performing photosynthesis • 5. UV radiation is dangerous to living things. Ozone accumulated over millions of years to block the majority of UV radiation and make land a safe place to live. • 6. Prokaryotes were the first organisms to live on land.

28. 7. How are eukaryotes different from prokaryotes? • Eukaryotes have: • Membrane-bound organelles • Nucleus • Prokaryotes do not have a nucleus nor membrane-bound organelles. Prokaryotic Cell vs. Eukaryotic Cell

29. 8. What is endosymbiosis? • Mutually beneficial relationship in which one organism lives within another • 9. The endosymbiotic theory proposes that larger cells engulfed smaller cells, which then began to live inside larger cells. • Mitochondria are descendants of aerobic, bacteria • Chloroplasts are descendants of photosynthetic bacteria

30. Endosymbiotic Theory Evidence of Theory Endosymbiotic Theory

31. 10. What are the 4 pieces of evidence that support the Endosymbiotic Theory? • Size and structure—both organelles are the same size as some bacteria • Genetic Material—both organelles contain their own DNA separate from the nucleus • Ribosomes—both organelle’s ribosomes are similar to bacterial ribosomes • Reproduction—both organelles reproduce by simple fission

32. 11. What are very early animal fossils scarce? • Because most animals at that time had soft body parts that did not fossilize well

33. 12. During the Paleozoic Era, marine invertebrates diversified, and marine vertebrates evolved. The first land plants evolved. Some arthropods, and then some vertebrates, left the oceans to colonize land.

34. 13. An arthropod is an animal that has a hard outer skeleton, a segmented body, and paired, jointed limbs. • First successful animal to live on land • Ex. Insects, crustaceans, etc… • 14. A vertebrate is an animal with a backbone. • Ex. Fish, amphibians, reptiles, etc…

35. 15. Reptiles, dinosaurs, and birds were the dominant animals during the Mesozoic Era, and the mammalian animals dominated the Cenozoic Era.