The Structure of the Earth The Earth, the planet we live on, is almost a sphere that is flattened at the poles (north and south), with a bulge at the equator. The Earth has three main LAYERS. The outer most layer is called the CRUST. It’s made of rock, mostly basalt, granite, and gabbro rocks.

The CORE has an outer core and an inner core section. The crust is about 12-40 miles thick under the land and only about 6-8 miles thick under the oceans. Under the crust is a melted, liquid zone called the MANTLE. It’s mostly made of silica and metal–rich minerals. It is very thick. The CORE has an outer core and an inner core section.

The outer core is mostly MELTED IRON while the inner core is mostly SOLID IRON. The inner core is under very high pressure caused by the gravity of the whole planet. Scientists have created the THEORY OF PLATE TECTONICS to explain what we see of the Earth’s crust.

The Crust is solid, we live on the crust. The Mantle is liquid, that’s were volcano lava comes from. The Outer Core is mostly LIQUID IRON metal. The Inner Core is mostly SOLID IRON metal.

The Theory of Plate Tectonics says… The Earth’s crust is made up of Tectonic Plates, that fit together like a jigsaw puzzle. These plates move, about six inches per year, because they are floating on the liquid mantle. At the boundaries between the plates we find volcanoes, earthquake fault lines, mountains, ocean trenches, and underwater mountain ridges. There are three specific types of plate boundaries…

A. Constructive Margins: Plates moving apart from each other, letting liquid mantle to percolate up, forming more crust. This happens often under the oceans. B. Destructive Margins: When two plates are pushing into each other. When two plates on land push together, they tend to form mountains we can see and climb. When it happens that a land plate and an ocean plate push together, the denser ocean plate goes UNDER the land plate, this forms a deep trench. C. Transform, or Conservative Margins: When two plates slide against each other, no new crust is formed, but it can cause earthquakes. The San Andreas Fault in California is like this.

Earth Scientists have a theory of a single continent called PANGAEA It is thought that at one time, more than 250 MILLION years ago, all the land on Earth was attached, and has gradually moved apart to the separate continents we have today.

6 Practice Questions 1. What does the theory of plate tectonics explain? A. Changes in the Earth’s crust B. Why there is extreme heat and pressure in the Earth’s core C. Changes in the Earth’s mantle. D. Changes in the composition of the Earth’s layers

6 Practice Questions 1. What does the theory of plate tectonics explain? A. Changes in the Earth’s crust The moving plates change or create the crust.

2. One similarity between Earth’s INNER and OUTER CORES is that both consist mostly of _______, although the two are different because in inner core _______, while the outer core ________. First blank Second blank Third blank iron is mostly gaseous granite is mostly liquid silica is mostly solid

2. One similarity between Earth’s INNER and OUTER CORES is that both consist mostly of IRON, although the two are different because in inner core mostly solid, while the outer core mostly liquid.

The Japan Trench off the coast of Japan is part of the boundary between an oceanic plate called the Pacific plate, and a continental plate called the Eurasian plate. At the trench, the Pacific plate is forced beneath the Eurasian plate, causing earthquakes in Japan. The Japan Trench is an example of which type of crustal feature? A. A tectonic plate B. A mid-ocean ridge C. A constructive margin D. A destructive margin

The Japan Trench off the coast of Japan is part of the boundary between an oceanic plate called the Pacific plate, and a continental plate called the Eurasian plate. At the trench, the Pacific plate is forced beneath the Eurasian plate, causing earthquakes in Japan. The Japan Trench is an example of which type of crustal feature? D. A destructive margin (where one plate if forced underneath another plate)

Which of the following provides evidence that the present-day continents were once a large continent that broke apart? A. Australia is a large, continent sized island. B. Eurasia is the largest land mass on Earth today. C. Eurasia and Antarctica are located in the southern hemisphere. D. The west coast of Africa seems to fit into the east coast of the Americas.

Which of the following provides evidence that the present-day continents were once a large continent that broke apart? D. The west coast of Africa seems to fit into the east coast of the Americas. This seems to go along with the idea that the continents once fit together as one whole land mass.

5. Which of the following is implied by the fact that the seafloor spreading at the Mid-Atlantic Ridge is causing the Atlantic Ocean to widen by about 5 centimeters per year? A. The Mid-Atlantic Ridge is thousands of miles long. B. The Mid-Atlantic Ridge is the largest underwater structure in the Atlantic Ocean. C. The continents of North America and Europe are moving apart. D. The continents of North America and Europe are growing larger at the Mid-Atlantic Ridge.

5. Which of the following is implied by the fact that the seafloor spreading at the Mid-Atlantic Ridge is causing the Atlantic Ocean to widen by about 5 centimeters per year? C. The continents of North America and Europe are moving apart. Because the crust is being created at the Mid-Atlantic Ridge, pushing these continents (slightly) apart all of the time.

6. Which of the following is a theory rather than a fact. A 6. Which of the following is a theory rather than a fact? A. The San Andreas Fault is the boundary between the North American Plate and the Pacific Plate. B. A single large landmass called Pangaea existed about 250 Million years ago. C. The Earth’s crust is composed of rocks like granite, basalt, and gabbro. D. Earthquakes often occur along tectonic plate boundaries.

6. Which of the following is a theory rather than a fact. B 6. Which of the following is a theory rather than a fact? B. A single large landmass called Pangaea existed about 250 Million years ago. The other three choices (A, C, and D) are all facts that can be proven true. Pangaea makes sense to scientists but none were there to see it that long ago.