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

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.

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.

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.

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.

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.

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.

Fossils still form today at the bottom of lakes, streams, oceans. 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.

Most fossils are found in sedimentary rocks. 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.

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.

Scientists use different methods to determine the age of fossils. 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.

Radiometric dating provides the specific age of rocks and fossils. 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.

Example of isotopes used in 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

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.

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.

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.

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.

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.

Paleozoic Era… Early Paleozoic Era Middle 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.

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.

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

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.

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.

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.

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

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.

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.

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.