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Change Over Time Chapter 2 Lesson 3 What is natural selection? • Dramatic changes have occurred on Earth over time: climate change, forests have become deserts, and seas have dried up • These changes affect organisms within the environments and they must change in order to survive • Charles Darwin developed a theory in the 1800s about how organisms change over time • Population- is all of the members of a singlespecies living in the same geographic area • Darwin noticed that there were variations in the populations (differences among members of the same species) What is natural selection? • Darwin’s theory is called natural selection • An organism with favorable variations is well suited to its environment. It is more likely to survive and reproduce than others. • Its variations will be passed on to the next generation • “Survival of the Fittest” is when the organisms with the favorable traits have survived. • A horse is an animal that has changed over time • Ancestors walked on several spread-out toes that probably helped them navigate swamps and mud. As the land dried, the horses developed single, flat hooves What is natural selection? • Throughout Earth’s history, many organisms have emerged and many have become extinct • Extinct Species no longer exist anywhere on Earth. • Species become extinct because they cannot adapt. What is evidence of change over time? • Scientists know that environments have changed because the history of change can be found in fossils • Fossils- are any remains, traces, or imprints of organisms that lived long ago. • Fossils can be formed when minerals in the sediment preserve bones, shells, or teeth of an animal • Fossils can also be formed when an insect is trapped in tree sap and the same hardens into amber • Footprints can be made when an animal walks across wet sand or mud and sediment quickly covers it and preserves the print. What Fossils tell us • Provide clues that tell us how environments have changed • For example: Scientists have found fossils of an ancient whale called Basilosaurus in Mississippi which tells us that Mississippi was once covered by water • Scientists can also predict past climate of an area • For example: Fossils of a warm-climate animal found in the arctic indicate that particular areas climate was not always artic like • Fossils provide clues about what organisms were like in the past and how they have changed (Smilodon) • Earth’s history is marked by geological and climate change and have caused some organisms to change over time • As environments change, organisms will adapt, move on, or die out How has Earth changed? • Earth’s history is measured in long stretches of time called eras-each era is divided into periods • Precambrian- Earth first became hospitable to life. Few fossils have been found • Paleozoic- life became abundant. Trilobites, fish, insects, amphibians, and reptiles appear during this era • Mesozoic- reveals the appearance of dinosaurs, mammals, birds, and flowering plants. Rock from this era indicate that life became extinct at the end of this era • Cenozoic- the era we live in. fossils show that some early mammals were very large. The most recent ice age occurred during this era.