6.1 Earth’s Structure

Fossils of the same plants and animals are found on different continents that are separated by wide oceans. How could this have happened and what does this suggest about the continents?

Compositional Layers of Earth Core Earth’s dense, metallic center made up mainly of metal iron Mantle Dense, thick middle layer Crust The surface layer composed mostly of silicon, oxygen, and aluminum.

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Describe Earth’s compositional layers. The crust, Earth’s surface layer, is rocky, thin, fractured, and composed mostly of silicon and oxygen. The mantle, Earth’s middle layer, is thick, dense, and rich in iron and magnesium. The core, Earth’s innermost layer, is dense and composed mostly of iron.

Two types of crust Continental crust Thicker than oceanic crust

Oceanic Crust Has almost twice as much iron, calcium, and magnesium than continental crust More dense and heavier than continental crust

Physical Structure of Earth Lithosphere A cool, rigid layer that includes the crust and the upper part of the mantle. Divided into pieces called tectonic plates.

Below the lithosphere, a layer of the mantle that is made of very slow-flowing solid rock Tectonic plates move Asthenosphere

Mesosphere Below the asthenosphere The lower part of the mantle.

Outer core A layer of liquid iron and nickel

Inner core Made mostly of iron and nickel Very hot, but it is solid because of extreme pressure

Continental Drift A single large landmass broke up into smaller landmasses to form the continents which then drifted to their present locations.

Evidence for Continental Drift: Fossils of the same plant and animal species are found on continents that are far from each other The location of mountain ranges and of similar types of rock. Ancient climatic zones supports this idea.

List three lines of evidence for continental drift. Three lines of evidence that support continental drift are the fit of the continents, the existence of the same fossils on different continents, and the locations of mountain ranges and similar types of rocks on different continents.

Alfred Wegener Wrote about continental drift Pangaea – the single large continent that gave rise to today’s continents. Pangaea existed 245 million years ago.

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Continental Drift

Briefly describe the movement of the continents over the past 245 million years. Beginning 245 million years ago, all of the present continents were joined in a single landmass called Pangaea. Approximately 135 million years ago, Pangaea split into a huge northern continent called Lauasia and a huge southern continent called Gonwanaland. By 65 million years ago they split into the continents we know today. Over the past 65 million years, the continents have moved slowly to their present positions.

Sea-Floor Spreading Mid-ocean ridges are underwater mountain chains that run through Earth’s ocean floor. There are patterns of magnetism in the sea-floor rocks. Magnetic reversal - the process by which Earth’s magnetic poles change places.

Sea-Floor Spreading At the mid-ocean ridge, magma rises through fractures in the sea floor. At the mid-ocean ridge, magma rises through fractures in the sea floor. Magma cools, and new rock forms. Magma cools, and new rock forms.

Sea Floor Spreading When new rock forms, the older rock gets pulled away from the mid-ocean ridge.When new rock forms, the older rock gets pulled away from the mid-ocean ridge. This process which new sea floor forms as old sea floor is pulled away is sea-floor spreading.This process which new sea floor forms as old sea floor is pulled away is sea-floor spreading.

Sea Floor Spreading

Review Questions 1. List the layers of Earth by their chemical composition and by their physical properties. The composition layers of Earth, beginning at Earth’s surface, are the crust, mantle, and core. They physical layers of Earth, beginning at Earth’s surface, are the lithosphere, asthenosphere, mesosphere, outer core, and inner core. 2. Describe evidence that supports the existence of Pangaea. The fit of the continents, the existence of the same fossils on different continents, and the locations of mountain ranges and similar types of rock on different continents support the existence of Pangaea.

3.Explain the process by which new sea floor forms at mid-ocean ridges. At mid-ocean ridges, magma rises through a series of fractures to the ocean floor. The magma cools and forms new rock. As this new rock forms, older rock is pushed away from the mid-ocean ridge. 4.If rocks found in North America and rocks found in Europe are the same, what does this indicate about the North American and European continents? This evidence would indicate that North America and Europe were once joined.