CHAPTER 14 HISTORY OF THE EARTH

1. 14.1 The record of life CHAPTER 14HISTORY OF THE EARTH

2. 14.1 The Record of Life… VOCABULARY • Isotope = atoms of the same element that have different numbers of neutrons. • Fossil = evidence of an organism that lived long ago. • Plate tectonics = the theory that explains how the continents move.

3. 14.1 The Record of Life • Paleontologist • Scientists who study ancient life. • Early Earth: • Very hot • Caused by the energy created by the colliding meteorites. • This heated the Earth’s surface. • The compression of minerals and decay of radioactive materials heated its interior. • Volcanoes • Spewed lava and gas – releasing pressure from the Earth’s interior. • The gases helped to form the Earth’s early atmosphere.

4. 14.1 The Record of Life • Earth’s Early Atmosphere… • Probably did not contain free oxygen, O2. • Water vapor, carbon dioxide and nitrogen were probably present. • We would not have been able to survive in early Earth’s atmosphere.

5. 14.1 The Record of Life • Earth formed about 4.6 billion years ago. • Theory states that the Earth cooled enough for water vapor to condense. • This may have led to millions of years of rainstorms with lightning. • Depressions filled – oceans formed • First life on Earth about 3.5 billion years ago. • Scientists are not certain that Earth formed in this way. • It is one theory – no direct evidence of the earliest years of Earth’s history.

6. Fossils… Clues to the Past • A fossil is evidence of an organism that lived long ago. • Scientists study fossils to learn about ancient species. • About 95% of the species that have existed are extinct – they no longer live on Earth. • Paleontologist = scientists who study ancient life. • Act like detectives… • They use fossils to understand events that happened long ago. • They use fossils to determine the kinds of organisms that lived during the past. • They also use fossils to try to learn about the organisms’ behaviors.

7. Paleontologists… Detectives to the Past Examples of fossil evidence: • Fossil bones and teeth • Indicate the size of animals • How they moved • What they ate • Ancient climate and geography • Studying fossils helps scientists to learn about past climates and geography. • Finding a fossilized plant suggests that the past climate was mild. • The condition, position, & location of rocks and fossils, scientists can make deductions about the geography of past environments.

8. Fossil Formation… • Fossils form • When organisms are buried in mud, sand or clay soon after they die. • Particles are compressed over a long period of time and harden into a type of rock. • This rock is called sedimentary rock. • Fossils still form today at the bottom of lakes, streams, oceans.

9. Fossil Formation… • Most fossils are found in sedimentary rocks. • Sedimentary rocks form at somewhat low temperatures and pressures. • This may prevent damage to the organism. • Sedimentary rocks form in horizontal layers, with younger layers closer to the surface. • Older fossils and rocks will be found in the deeper layers.

10. Fossil Formation… • Fossils are not usually found in other types of rock for a number of reasons. • Metamorphic rocks form when heat, pressure, and chemical reactions change other rocks. • i.e., Marble / limestone; slate / shale… • These conditions often destroy any fossils that were present in the original sedimentary rock.

11. Relative Dating… • Scientists use different methods to determine the age of fossils. • Figure 14.2 • If rock layers have not been disturbed, the older layers will be below the younger layers…. Younger layers will be on top of older layers. • This also means that the fossils found in the lower layers are older than the fossils found in the layers closer to the surface. • Determines relative age (older than, younger than) and order of appearance of the species preserved as fossils in the layers.

12. Radiometric Dating… • Relative dating does not determine the actual age in years of a fossil or rock. • Radiometric dating provides the specific age of rocks and fossils. • Scientists use radioactive isotopes in rocks to find the exact age in years. • Radioactive isotopes are atoms with unstable nuclei. • They break down over time. • They give off radiation. • A radioactive isotope forms a new isotope after it decays.

13. Radiometric Dating… • The half-life is the length of time needed for half of the atoms of the isotope to decay. • The ratio of radioactive isotope to the new isotope formed as it decays… • helps scientists to determine the approximate age of rocks. • Example of isotopes used in radiometric dating… • Potassium-40 decays to argon-40

14. Radiometric Dating… For accurate, consistent values – • Many rock samples are used with a variety of testing methods. • Errors can happen if • the rock has been heated. • This will cause some of the radioactive isotopes to be lost or gained. • The age will be inaccurate in this case.

15. Geologic Time Scale… • Calendar of Earth’s history. • Based on evidence from Earth’s rocks and fossils. • Figure 14.4 • Divided into 4 large sections. • Precambrian • Paleozoic Era • Mesozoic Era • Cenozoic Era P P Me C • Era is a large division in the scale and equals a very long period of time. • Each era is subdivided into periods.

16. Geologic Time Scale, cont’d… • Divisions are distinguished by the organisms that lived during that time period. • Fossil record indicates that there were several mass extinctions that fall between time divisions. • Mass extinction = event that occurs when many organisms disappear from the fossil record nearly all at once.

17. Precambrian • Accounts for about 87% of Earth’s history. • At the beginning of the Precambrian, about 3.4 billion years ago… • Unicellular organisms, bacteria, were the only life form. • About 2.1 billion years ago, eukaryotic organisms appeared. • At the end of the Precambrian, about 543 million years ago, multicellular eukaryotes, i.e., sponges and jellyfishes, diversified and filled the oceans.

18. Paleozoic Era • Many more types of animals and plants present during this time. • Some were preserved in the fossil record. • The earliest part of the Paleozoic Era is the Cambrian Period. • Referred to as the “Cambrian explosion” of life. • Fossil record shows an enormous increase in the diversity of life forms during this time. • Oceans teemed with many types of animals.

19. Paleozoic Era… • Early Paleozoic Era • Vertebrates appeared. • Ferns and early seed plants appeared. • Middle Paleozoic Era • 4-legged animals appeared, i.e., amphibians. • Late Paleozoic Era • Reptiles appeared on land and flourished. • Largest mass extinction recorded marked the end of the Paleozoic Era.

20. Paleozoic Era End of the Paleozoic Era: • Largest mass extinction recorded in the fossil record marked the end of the Paleozoic. • 90% of Earth’s marine species and 70% of the land species disappeared at this time.

21. Mesozoic Era • Divided into three periods. • Triassic Period • Oldest period • Mammals appeared • Early mammals were small, mouselike • Dinosaurs and reptiles appeared • Ferns – huge fern forests

22. Mesozoic Era, cont’d… Jurassic Period – middle of the Mesozoic Era • Modern birds evolved from one of the groups of dinosaurs. • This happened toward the end of this period. • Archaeopteryx • Small bird discovered in Germany • Had feathers, which is a birdlike feature • Present day bird – hoatzin, figure 14.8B, pg. 378 • Reptilian features – claws on its wings – during its first few weeks of life • This evidence suggests that birds evolved from dinosaurs.

23. A Mass Extinction! • Cretaceous • Last period of the Mesozoic Era • Many new types of mammals appeared • Flowering plants flourished • Mass extinction of dinosaurs marked the end of the Cretaceous Period • Scientists estimate that more than 2/3 of all living species during this time became extinct. • Cause of the Extinction? • One idea is that a large meteorite collision caused the mass extinction.

24. Mass Extinction, cont’d… • A huge collision could have filled the atmosphere with thick, possibly toxic dust. • This would have changed the climate. • Many species would not have been able to survive the changed climate. • Large crater found in the waters off eastern Mexico • Crater was dated back to the Cretaceous Period. • Scientists believe this was the impact site.

25. Changes During the Mesozoic Era • Geological events during this era changed the places where species lived. • These events affected the distribution of the species on Earth. Theory of Continental Drift • Earth’s continents have moved during Earth’s history and are still moving today. • 6 cm per year • Same rate as the growth of hair

26. Changes During the Mesozoic Era • Early in the Mesozoic • The continents were merged into one large landmass. • The supercontinent broke up. • Pieces drifted apart. • Plate Tectonics – Theory that explains how the continents move.

27. Plate Tectonics, cont’d… • Earth’s surface is made of several rigid plates. • These plates drift on top of a fluid, partially molten layer of rock. • Plates are constantly moving. • Spreading apart • Sliding by • Or pushing against each other. • The movements affect organisms. • i.e., Descendants living on plates that are moving apart may be living in areas with very different climates.

28. Cenozoic Era • Began about 65 million years ago. • Era in which we now live. • Mammals flourish in the early part of this era. • Primates appear – group of animals which humans belong to. • Primates have diversified greatly over the past 65 million years. • Modern man appeared approximately 200,000 years ago.