Chapter 5 Section 1 Geologic History

ObjectiveObjective Contrast relative dating with absolute dating.Contrast relative dating with absolute dating.

Relative DatingRelative Dating Scientists use different methods to determine the age of objects in sedimentary rocks.Scientists use different methods to determine the age of objects in sedimentary rocks. One method, Relative dating, examines a fossil’s position within rock layers to estimate its age.One method, Relative dating, examines a fossil’s position within rock layers to estimate its age.

The bottomlayers of rock are usually the oldest, and the top layers are usually the youngest.The bottom layers of rock are usually the oldest, and the top layers are usually the youngest. Scientists can use the order of rock layers to determine the relative age of objects within the layers.Scientists can use the order of 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.For example, fossils in the bottom layers are usually older than fossils in the top layers.

The Geologic ColumnThe Geologic Column To make relative dating easier, geologists combine data from all of the known rock sequences around the world.To make relative dating easier, geologists combine data from all of the known rock sequences around the world.

From this information, geologists created the geologic column — an ideal sequence of rock layers that contains all of the known fossils and rock formations on Earth, arranging layers from oldest to youngest.From this information, geologists created the geologic column — an ideal sequence of rock layers that contains all of the known fossils and rock formations on Earth, arranging layers from oldest to youngest.

PaleontologyPaleontology Paleontology is the science involved with the study of past life. Scientists who study past life are called paleontologists.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. Paleontologists collect data by studying fossils.

Section 2 Looking at FossilsSection 2 Looking at Fossils

ObjectiveObjective Explain how fossils can be used to determine the history of changes in environments and organisms.Explain how fossils can be used to determine the history of changes in environments and organisms.

The remains or physical evidence of an organism preserved by geologic processes is called a fossil.The remains or physical evidence of an organism preserved by geologic processes is called a fossil. Trace fossils are any naturally preserved evidence of animal activity.Trace fossils are any naturally preserved evidence of animal activity.

A cavity in rock where a plant or animal was buried is called a mold.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.A cast is an object that is created when sediment fills a mold and becomes rock.

History of Changing OrganismsHistory of Changing Organisms Scientists study the relationships between fossils to interpret how life has changed over time.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 changeSince the fossil record is incomplete, paleontologists look for similarities between fossils over time to try to track change.

Using Fossils to Date RocksUsing Fossils to Date Rocks Scientists have found that particular types of fossils appear only in certain layers of rock.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.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.If the organism lived for a relatively short period of time, its fossils would show up in limited layers.