Unit B Chapter 8 Plate Tectonics Earth’s Variety

Unit BChapter 8Plate Tectonics Earth’s Variety Many different types of landforms plateau – raised flatland waterfall mountain plain – flatlands with few trees valley – low land between mountains ridge – long row towering mountains on ocean floor volcano trench – long narrow cut in ocean floor

Unit BChapter 8Plate Tectonics

Earth’s LayersCrust outermost solid layer of Earth-soil & rock from 5 to 30 kilometers thick compared to a thin shell

Mantle thick layer below crust – largest part outer part – solid inner part – partly melted rock

Core innermost layer compact/dense about 5000°C outer part – liquid inner part - solid


Earth’s PlatesLithosphere crust and solid part of mantle broken into pieces – tectonic plates 12 large plates many smaller ones Most made of continental and oceanic crust Most of U.S. on North Amer. Plate Plates float atop inner mantle

Earth has a variety of surface features and several layers.


Continental drift - theory that continents have drifted apart, and continue to do so Alfred Wegener – 1912 – German same fossils plants/animals on 2 different continents matching rock layers rejected by other scientists


Spreading Ocean Bottom Mid-Atlantic Ridge – long, deep trenches and a chain of mountains on floor on Atlantic Ocean.


Sea floor spreading – Magma pushes up, cools, forms new crust, and moves old crust aside. Plates are moving away from each other, and the ocean floor spreads apart. Magma rises to fill the gap.


Hot liquids weigh less and float above cooler liquids. Convection – force that moves Earth’s plates Hot, melted rock rises, then cools, gets heavy and sinks again. When mantle moves, plates floating on it also move.


Proof of Continental Drift Seafloor spreading Patterns in magnetism

Evidence of continental drift is found in fit of continents, distribution of fossils, and sea floor spreading.


Explaining Earth’s FeaturesPlate tectonics lithosphere contains 20 moving plates that float on a layer of partly meted rock.

Scientists measure the movement of plates using laser beams from space satellites.

Scientists make predictions about where the continents will be in 50 million years.


Plate boundaries areas where 2 plates meet

Spreading boundary – plates move away from each other.

Colliding boundary – plates push against each other.

Fracture boundary – plates slide past each other.

Earth’s plates are constantly moving to give earth its many features.


Earthquakes Caused by sudden shifting of rock as tectonic plates shift position. Pressure builds up and when it gets too strong the rocks suddenly move and an earthquake occurs. Focus – underground point where earthquake occurs Epicenter – point on Earth’s surface directly above the focus


Energy from an earthquake is released in waves Causes ground to move: back and forth up and down in a circular motion As waves spread out they lose energy Worst damage usually occurs closest to the epicenter. Most earthquakes take place near the edges of plates.


Strength measured on a magnitude scale (Richter scale) Each increase of 1 represents 31 times more energy that’s released.

Effects of an earthquake depends on: size/strength distance from epicenter kind of rock in the area types of buildings number of people who live there


Volcanoes Occurs when magma from mantle comes through crust. Occurs near plate boundaries. a plate sinks beneath another sinking crust melts pressure builds up magma explodes lava spreads over surface of earth Quiet flows are less destructive and more common.


Predicting Seismometers – detect tremors Tiltmeters – detect changes in tilt of earth Laser beams – detect movement between plates Ways to stay safe Prepare a safety plan Get under table/desk Stay away from falling objects Move to open area

Most volcanoes and earthquakes occur along plate boundaries.


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Unit B Chapter 8 Plate Tectonics Earth’s Variety