Plate Tectonics Evidence of Earth's Change Over Time PDF

EXPLAIN READ ABOUT IT TEKS 7.10A, 7.1H, 7.4A Evidence of Earth’s Change Over Time Why do Africa and South America look like puzzle pieces? Were the two continents once connected? In...

EXPLAIN READ ABOUT IT TEKS 7.10A, 7.1H, 7.4A Evidence of Earth’s Change Over Time Why do Africa and South America look like puzzle pieces? Were the two continents once connected? In 1912, a German scientist named Alfred Wegener asked this very question. The answer transformed how we think about Earth. Vocab Tip A hypothesis is Plate Tectonics and Continental Drift an idea that can Wegener noticed that some continents seem to fit together, and this be tested by experimentation or led him to form the radical hypothesis that the different continents were investigation. It is once connected. But he needed more evidence to develop a theory. based on evidence In science, a theory is an explanation for why a phenomenon happens. and serves as a starting point in Theories must be supported by evidence. science. In contrast, Wegener studied the shape of continents, rock types, and fossils in a theory develops when a hypothesis different parts of the world. Together, the evidence suggested that, is shown to be true at one time, the continents had been fused together but had slowly through a broad drifted apart over time. This idea became known as the theory of range of studies. continental drift. Scientists knew that the continents moved, but they didn’t know why until decades later, when they developed the theory of plate tectonics. Copyright © Savvas Learning Company LLC. All Rights Reserved. Earth’s surface is broken up into more than a dozen distinct plates, called tectonic plates, that slowly move in different directions. Moving Plates Tectonic plates move a few inches per year, EURASIAN about the same rate PLATE NORTH EURASIAN PLATE your fingernails grow. AMERICAN PLATE Their movement JUAN DE FUCA PLATE causes continents to CARIBBEAN PHILIPPINE PLATE slowly drift away from PLATE AFRICAN PLATE each other. PACIFIC PLATE COCOS PLATE SOUTH AMERICAN NAZCA PLATE INDO-AUSTRALIAN PLATE PLATE SCOTIA PLATE ANTARCTIC PLATE ANTARCTIC PLATE 228 PLATE TECTONICS Evidence of Earth’s Change Over Time   he shape of the continents made them seem like giant puzzle pieces. T This was an important piece of evidence. Wegener hypothesized that, long ago, most or all of the continents were assembled as a supercontinent, which he called Pangaea. Other scientists have hypothesized the existence of supercontinents that formed even earlier than Pangaea. Earth‘s Changing Surface Tectonic plates have been moving for billions of years. Over time, the locations and sizes of continents and oceans have changed—and they are still changing. About 250 million years ago Most of Earth’s land was joined together into one large supercontinent called Pangaea. About 115–200 million years ago Pangaea began to break apart, due to tectonic plate movement, eventually forming smaller landmasses. Copyright © Savvas Learning Company LLC. All Rights Reserved. Today Over millions of years, Earth’s landmasses continued to move apart eventually becoming the continents we see today. Evidence of Earth’s Change Over Time PLATE TECTONICS  229  Fossil Evidence Photo Credits: De Agostini Picture Library/Universal Images Group North America LLC/Alamy Stock Photo; Corbin17/Alamy Stock Photo Fossils are bones and other traces of very ancient animals and plants. By studying the fossils in an area, people can know what organisms once lived there, what the climate was like, and what the environment was like. Fossils provide evidence for the theory of continental drift. Glossopteris (glaw SAHP tuh ris) was a fernlike plant that lived 250 million years ago. Today, its fossils are found on five different continents. Mesosaurus (may so SAW rus) was a stocky lizard that was unlikely to swim long distances or in salty water. Today, its fossils are found on two continents that are separated by a large ocean. This animal could not swim across a salty ocean—why are its fossils in two continents? Fossil Evidence of Continental Drift Fossils like Glossopteris and Mesosaurus are evidence for the theory that, long ago, all continents were joined together in a supercontinent. Over time, they slowly drifted apart. Use Visuals Look closely at AFRICA the diagram and photographs of the INDIA two different fossils. Compare where the two different kinds of fossils are found. Then, SOUTH AMERICA explain how you can tell on which modern continents AUSTRALIA each different fossil ANTARCTICA Copyright © Savvas Learning Company LLC. All Rights Reserved. occurs. Mesosaurus fossils are found in both South America and Africa. Glossopteris fossils are found on five different continents. 230 PLATE TECTONICS Evidence of Earth’s Change Over Time  Superposition and Rock Evidence Geologists analyze the positions of rock layers to determine their Vocab Tip age and identify how they change over time. They use the law of superposition to determine the ages of sedimentary rock layers, which In science, the term usually form in horizontal layers. In undisturbed sedimentary rock layers, law describes a repeated pattern according to the law of superposition, the oldest layer is at the bottom observed in and the youngest layer is at the top. nature. Unlike a theory, a law does Rocks and rock layers provide evidence to support the theory of not provide an continental drift. Rock layers and the fossils they contain form a geologic explanation for the observed pattern. record of Earth’s history and can reveal how Earth has changed over Describe to a time. Glaciers leave striations, deep scratches, on the surface of rocks. partner how the Scientists found similar glacial striations on rocks in Africa and South two terms theory and law are used in America, which supports the idea that these two continents were once everyday life. joined together and covered by a single glacier. Superposition and the Age of Rock Layers Each layer of undisturbed rock is older than the layer above it and younger than the layer below it. When comparing rock layers, the youngest rock layer is usually found above older rock layers. Fossils are the same age as the rock layer in which they are preserved. These fossils are in the same rock layer, so they are from organisms that lived at around the same Copyright © Savvas Learning Company LLC. All Rights Reserved. time. On different continents, the same types of fossils have been found in the same rock layer, suggesting the continents were once joined. Certain fossils, called index fossils, are particularly helpful to geologists in matching rock layers of the same age. They are the traces of organisms that were widely distributed but existed for a relatively short time. The oldest rock layers are usually found below younger rock layers, meaning fossils in these layers are usually older than the fossils found above them. Evidence of Earth’s Change Over Time PLATE TECTONICS  231 Apply It 1. Describe Describe how plate tectonics and the theory of Write About It continental drift suggest Earth has changed over time. Include one piece of evidence. Write a short paragraph in which you describe your experience reading about how Earth has changed over time. Use new words you have learned in your paragraph. What did you find easy or difficult to understand? 2. SEP Develop Models Draw a diagram showing three or more rock layers. In one layer, draw a fossil of a fish and a clam. In another layer, draw the fossil of leaf. In a blank layer, write “sandstone.“ Fill in any other remaining layers with either fish or leaf fossils. Label the layers from youngest to oldest. Use your model to describe how superposition provides evidence for how Earth has changed over time. Copyright © Savvas Learning Company LLC. All Rights Reserved. 232 PLATE TECTONICS Evidence of Earth’s Change Over Time