Chapter 5 The Fossil Record Preview Section 1 Geologic HistoryGeologic History Section 2 Looking at FossilsLooking at Fossils Section 3 Time Marches OnTime Marches On Concept Mapping

Chapter 5 Uniformitarianism: assumes that geologic processes that are shaping the Earth today have been at work throughout Earth’s history. Catastrophism: the principle that all geologic change occurs suddenly –catastrophism thought that Earth’s mountains, canyons, and seas formed during rare, sudden events called catastrophes. Geologic History Section 1 Geologic History

Chapter 5 Section 1 Geologic History

Chapter 5 Most geologic change is gradual and uniform. But catastrophes that cause geologic change have occurred during Earth’s long history. Asteroid and comet strikes to Earth, for example, have caused rapid change. Modern Geology—A Happy Medium Section 1 Geologic History

Chapter 5 Some scientists think an asteroid strike 65 million years ago caused the dinosaurs to become extinct. Modern Geology—A Happy Medium, continued Section 1 Geologic History

Chapter 5 Scientists can use two methods to determine the age of objects in sedimentary rocks. Relative dating: examines a fossil’s position within rock layers to estimate its age. –Look for key words such as before, after, older, younger –Examples: Before the dinosaurs existed Older than my brother After the extinction of dinosaurs Relative Dating Section 1 Geologic History

Chapter 5 Relative Dating, continued The bottom layers of rock are usually the oldest, and the top layers are usually the youngest. Scientists can use the order of these rock layers to determine the relative age of objects within the layers. For example, fossils in the bottom layers are usually older than fossils in the top layers. Section 1 Geologic History

Chapter 5 The Geologic Column To make relative dating easier, geologists combine data from all of the known rock sequences around the world. From this information, geologists create the geologic column—an ideal sequence of rock layers that contains all of the known fossils and rock formations on Earth. These layers are arranged from oldest to youngest. Relative Dating, continued Section 1 Geologic History

Chapter 5 Section 1 Geologic History

Chapter 5 Scientists can use absolute dating to more precisely determine the age of a fossil or rock. Absolute dating: to measure the age of fossils or rocks in years. –Examples: 5780 years ago Born in 1900 At the beginning of the Triassic period Absolute Dating Section 1 Geologic History

Chapter 5 Section 1 Geologic History

Chapter 5 Paleontology is the science involved with the study of past life. Scientists who study past life are called paleontologists. Paleontologists collect data by studying fossils, the remains of organisms preserved by geological processes. Paleontology—The Study of Past Life Section 1 Geologic History

Chapter 5 Vertebrate and invertebrate paleontologists study the remains of animals. Paleobotanists study fossils of plants. Other paleontologists reconstruct past ecosystems, study the traces that animals left behind, and piece together the conditions under which fossils formed. Paleontology—The Study of Past Life, continued Section 1 Geologic History

Chapter 5 Fossilized Organisms The remains or physical evidence of an organism preserved by geologic processes is called a fossil. 1.Fossils in rocks can form when an organism dies and is quickly covered by sediment. –When the sediment becomes rock, hard parts of the organism are preserved. Section 2 Looking at Fossils

Chapter 5 Fossilized Organisms, continued 2.Fossils in amber are entire organisms preserved inside hardened tree sap, called amber. –If an insect is caught in sticky tree sap, the sap covers its entire body and hardens quickly. –Some of the best insect fossils, as well as frogs and lizards, have been found in amber. Section 2 Looking at Fossils

Chapter 5 Fossilized Organisms, continued 3.Petrifaction is a process in which minerals replace the organism’s tissues. –Permineralization, pore space in an organism’s hard tissue (like bone or wood) is filled up with mineral. –Replacement, minerals completely replace the tissues of the organism. Section 2 Looking at Fossils

Chapter 5 Fossilized Organisms 4. Fossils in asphalt, asphalt wells up and forms thick, sticky pools at Earth’s surface. –These asphalt pools can trap and preserve many organisms. The La Brea asphalt deposits in Los Angeles, California have preserved organisms for at least 38,000 years. Section 2 Looking at Fossils

Chapter 5 Fossilized Organisms, continued 5.Frozen Fossils In 1999, scientists removed a 20,000-year-old woolly mammoth that was frozen in the Siberian tundra. –These mammoths became extinct about 10,000 years ago. –Because cold temperatures slow down decay, the mammoth was almost perfectly preserved. Section 2 Looking at Fossils

Chapter 5 Trace fossils are any naturally preserved evidence of animal activity. –Tracks are an example of a trace fossil. They form when animal footprints fill with sediment. –Tracks can reveal size and speed of an animal, and whether it traveled in groups. Other Types of Fossils Section 2 Looking at Fossils

Chapter 5 Burrows are another trace fossil. –Burrows are shelters made by animals that bury themselves in sediment, such as clams. –Another type of trace fossil is coprolite, or preserved animal dung. Other Types of Fossils, continued Section 2 Looking at Fossils

Chapter 5 Other Types of Fossils, continued Molds and casts are two more examples of fossils. A cavity in rock where a plant or animal was buried is called a mold. A cast is an object that is created when sediment fills a mold and becomes rock. Section 2 Looking at Fossils

Chapter 5 The Information in the Fossil Record The fossil record gives only a rough sketch of the history of life on Earth. Most organisms never become fossils. Many fossils have yet to be discovered. Using Fossils to Interpret the Past Section 2 Looking at Fossils

Chapter 5 Organisms with hard body parts have left more fossils than those with soft body parts. Organisms that lived in areas that favored fossilization have also left more fossils. Using Fossils to Interpret the Past, continued Section 2 Looking at Fossils

Chapter 5 But fossils can show a history of environmental change. For example, the presence of marine fossils on mountaintops in Canada means that these mountains formed at the bottom of the ocean. Marine fossils can also help scientists reconstruct ancient coastlines and detect the presence of ancient seas. Using Fossils to Interpret the Past, continued Section 2 Looking at Fossils

Chapter 5 Scientists can use fossils of plants and land animals to reconstruct past climates. By examining fossils, scientists can tell whether the climate of an area was cooler or wetter than that climate is now. Using Fossils to Interpret the Past, continued Section 2 Looking at Fossils

Chapter 5 History of Changing Organisms Scientists study the relationships between fossils to interpret how life has changed over time. Since the fossil record is incomplete, paleontologists look for similarities between fossils over time to try to track change. Using Fossils to Interpret the Past, continued Section 2 Looking at Fossils

Chapter 5 Scientists have found that particular types of fossils appear only in certain layers of rock. By dating rock layers above and below these fossils, scientists can determine the time span in which the organism lived. If the organism lived for a relatively short period of time, its fossils would show up in limited layers. Using Fossils to Date Rocks Section 2 Looking at Fossils

Chapter 5 Index fossils are fossils of organisms that lived for a relatively short, well-defined geologic time span. To be index fossils, these fossils must be found worldwide. Using Fossils to Date Rocks, continued Section 2 Looking at Fossils

Chapter 5 Ammonites of the genus Tropites are index fossils. Using Fossils to Date Rocks, continued Section 2 Looking at Fossils

Chapter 5 These ammonites were marine mollusks similar to modern squids. Tropites lived between 230 million and 208 million years ago. Fossils of these ammonites are index fossils for that time period. Using Fossils to Date Rocks, continued Section 2 Looking at Fossils

Chapter 5 Trilobites of the genus Phacops are also index fossils. Trilobites are extinct. Their closest living relative is the horseshoe crab. Using Fossils to Date Rocks, continued Section 2 Looking at Fossils

Chapter 5 Phacops lived about 400 million years ago. When scientists find fossils of trilobites anywhere on Earth, they assume the rock layers are also approximately 400 million years old. Using Fossils to Date Rocks, continued Section 2 Looking at Fossils

Chapter 5 Earth is about 4.6 billion years old. Paleontologists find a record of Earth’s history in rock formations and fossils around the world. The Rock Record and Geologic Time One of the best places in North America to see Earth’s history recorded in rock layers is Grand Canyon National Park in northwestern Arizona. Geologic Time Section 3 Time Marches On

Chapter 5 Geologic Time, continued The Colorado River has cut the Grand Canyon nearly 2 km deep in some places. Over the course of 6 million years, the river has eroded countless layers of rock. These layers represent almost half, or nearly 2 billion years, of Earth’s history. Section 3 Time Marches On

Chapter 5 Section 3 Time Marches On

Chapter 5 The geologic column represents the billions of years that have passed since the first rocks formed on Earth. Geologists study a total of 4.6 billion years of Earth’s history! To make their job easier, geologists have created the geologic time scale, a scale that divides Earth’s history into distinct intervals of time. The Geologic Time Scale Section 3 Time Marches On

Chapter 5 Section 3 Time Marches On

Chapter 5 Geologists have divided Earth’s history into sections of time. The largest divisions of time are eons. –The four eons are the Hadean eon, the Archean eon, the Proterozoic eon, and the Phanerozoic eon. The Geologic Time Scale, continued Section 3 Time Marches On

Chapter 5 The Phanerozoic eon is divided into three eras, which are the second-largest divisions of geologic time. The three eras are further divided into periods, which are the third-largest divisions of geologic time. Periods are divided into epochs, the fourth-largest divisions of geologic time. The Geologic Time Scale, continued Section 3 Time Marches On

Chapter 5 The Paleozoic Era—Old Life The Paleozoic era lasted from about 543 million to 248 million years ago. The Paleozoic era is the first era well represented by fossils. Marine life flourished at the beginning of the Paleozoic era. However there were few land animals. The Geologic Time Scale, continued Section 3 Time Marches On

Chapter 5 By the middle of the Paleozoic era, all modern groups of land plants had appeared. By the end of the era, amphibians and reptiles lived on the land, and insects were abundant. The following slide shows what life might have looked like in the late Paleozoic era. The Geologic Time Scale, continued Section 3 Time Marches On

Chapter 5 The Late Paleozoic Era Section 3 Time Marches On

Chapter 5 The Paleozoic era came to an end with the largest mass extinction in Earth’s history. Some scientists believe that ocean changes were a likely cause of this extinction. The event killed nearly 90% of all species. The Geologic Time Scale, continued Section 3 Time Marches On

Chapter 5 The Mesozoic Era—The Age of Reptiles The Mesozoic era began about 248 million years ago. The Mesozoic era is called the Age of Reptiles because reptiles such as dinosaurs dominated the land. The Geologic Time Scale, continued Section 3 Time Marches On

Chapter 5 Small mammals appeared about the same time that the dinosaurs did. Birds appeared in the late Mesozoic era. Many scientists think that birds developed directly from a type of dinosaur. The Geologic Time Scale, continued Section 3 Time Marches On

Chapter 5 At the end of the Mesozoic era, about 15% to 20% of all species on Earth became extinct. This mass extinction event wiped out the dinosaurs. Global climate change may have caused this extinction. The Geologic Time Scale, continued Section 3 Time Marches On

Chapter 5 The Cenozoic Era—The Age of Mammals The Cenozoic era began about 65 million years ago and continues to the present. This era is known as the Age of Mammals. During the Mesozoic era, mammals had to compete with dinosaurs and other animals for food and habitat. The Geologic Time Scale, continued Section 3 Time Marches On

Chapter 5 After the mass extinction at the end of the Mesozoic era, mammals flourished. Unique traits may have helped these mammals survive the environmental changes that probably caused the extinction of the dinosaurs. These traits include the ability to regulate internal body temperature and to develop young inside the mother. The Geologic Time Scale, continued Section 3 Time Marches On