Unit 2: “Earth and Space Science Chapter 4: “Our Dynamic Earth” Lesson 1: ”Plate Tectonics”

What are Earth’s layers? Earth is made of layers that differ in composition (what it’s made of), thickness, and temperature. The three layers of Earth are the crust, mantle, and core.

Diagram of Earth’s Layers

The core… The core is divided into the inner core and the outer core. The outer core is made of liquid metals. The inner core is made of solid metals. The Earth’s core is under high pressure.

The mantle… The mantle is a thick layer of solid and molten rock that surrounds the core. The mantle is divided into two parts---upper and lower. The top layer of the mantle is solid rock. The crust of the Earth and the top layer of the mantle make up the lithosphere. The rest of the upper mantle is partly melted rock and is called referred to as the asthenosphere. The lower mantle is solid rocl.

The crust… The crust is a thin layer of solid rock that makes up the outermost layer of Earth. While the thickness varies (is different) from place to place it is generally very thin. In comparison, the crust is like the skin on an apple.

The hydrosphere… All Earth’s liquid and solid water including oceans, lakes, rivers, glaciers, and groundwater makes up its hydrosphere. The hydrosphere covers about 70% of Earth’s surface. Most of Earth’s water is salt water. Of the small fraction of Earth’s water that is freshwater, most of it is frozen…trapped as ice around the North Pole and South Pole.

What makes up the hydrosphere?

Landforms A landform is a physical feature on the surface of Earth. Examples include mountains, canyon, hills, mesas, islands, and deserts. Each landform has specific characteristics and forms in a different way.

Types of landforms…

Are the continents moving? Alfred Wegener developed the theory of continental drift. Wegener noticed that the coastlines of continents appeared to fit together like pieces of a giant jigsaw puzzle. This supercontinent was named Pangaea. It is believed that over hundreds of millions of years the continents slowly separated and moved to the positions in which they are currently located.

Pangaea: A “Supercontinent” Pangaea Today

Pangaea: Fact or Fiction? Mountains on the east coast of South America had the same types of rocks as the mountains on the west coast of Africa. A fossil of a freshwater reptile called Mesosaurus has been found in very old rocks in South America and Africa. Mesosaurus could not have swum through the salt water of the Atlantic Ocean but could have traveled across the larger continent through freshwater rivers.

What causes the continents to move? Scientists have developed the theory of plate tectonics to explain how forces deep within Earth can cause seafloors to spread and continents to move. The lithosphere is made of huge plates of solid rock and the continents move with these plates. The almost melted rock of the asthenosphere acts like a conveyor belt on which the plates can move.

Plate Tectonics can cause… As the plates move magma (hot, melted rock deep within Earth) from the mantle pushes up toward the surface. This upward movement of magma causes tension, or a stretch or push, on the plates. This can result in seafloor spreading or the creation of mid-ocean ridges. As plates collide, one plate can sink under another plate which is called subduction…one plate ducks under the other.

How do mountains form? In addition to seafloor spreading, mid-ocean ridges, and subduction, plate tectonics can cause mountains to form. When plates collide, the force that results is called compression. Compression causes the ground above to be forces upward thereby creating folded mountains like the Himalayas located in India and Asia. The Himalayas grow about 0.2 inches each year.

How do mountains form? When plates spread apart faults form. Faults are deep cracks in Earth’s crust where rocks move in opposite directions. As a result of the tension between the faults, one block of rock moves down relative to the other block of rock forming fault-block mountains. The Sierra Nevada located in the western United States are an example of fault-block moutains.