Earth's+Surface

All the continents were once part of a huge supercontinent. It broke up and the pieces drifted apart on tectonic plates. The plates float on the liquid rock of the mantle. They only move an inch or two a year. When they collide, they can cause mountains or volcanoes to form. They can also cause earthquakes when they collide, slide past each other, or one dives under the other. The San Andreas Fault is where two plates meet in California. Help design a bridge that will withstand an earthquake. || Continental Drift In the early 1900s, Alfred Wegener noticed that the coastlines of Africa and South America looked like pieces of puzzle that should fit together, as if they had once been attached. He found other similar patterns on both sides of the Atlantic Ocean that had the same kinds of fossils. He concluded that all the continents used to be connected millions of years ago forming Pangaea until they drifted apart. See if you can reconstruct Pangaea on the interactive map. Check out the other links explaining earthquakes, plate tectonics- boundaries and motion, mountains, volcanoes and hot spots. || Geographers and mapmakers have long speculated that the continents were fragments of larger landmasses, and that continents were not always in their present locations on Earth. Not only do the coastlines of continents appear to fit together, but the continental shelves and slopes submerged in the water of the oceans also fit together. Scientists believe Rodinia may have been the first supercontinent, over a billion years ago. Pannotia, another supercontinent, is believed to have been formed 600 million years ago. Laurasia and Gondwanaland combined to form Pangaea 225 million years ago. || Plate Tectonics Plate tectonics is a theory that the Earth's outer shell is divided into several different plates that are able to move and glide over the Earth's mantle. The mantle is a rocky inner layer that lies above the Earth's core. Features on the planet include deep oceans and tall mountains which can all be explained to exists because of these plates and their movement. Here you will find a 40 minute documentary discussing plate tectonics, continental drift, and an exploration of the ocean floor for evidence of these plates. || Follow the evolution of a theory as you see how scientists have come to understand how our planet works. Learn about continental drift and see how the theory of plate tectonics came about. The evidence for continental drift is provided and sea floor spreading is discussed. The theory of plate tectonics is examined in depth beginning with a definition of a plate and with discussions of constructive and deconstructive plate boundaries. Understand plate tectonic motion and learn about the driving forces that cause plates to move. The implications of plate tectonics are explained. || Understanding Earthquakes Spreading ridges under the ocean allow magma to rise up from inside the earth. Subduction zones create mountains as two plates collide and the edge of one is forced under the other. The most common place for geologic activity is places where continental margins are near subduction zones or spreading ridges. Geologic activity is rarer in the center of a continent or plate, but can occur in rift zones. The New Madrid Seismic Zone was once a rift but is now being pushed together. It is the most seismically active area in the U.S. east of the Rockies. || You will really like this color animation of the breakup of the ancient continent of Pangea. When you click onto the world map, you can watch as the continent breaks up and the sea floor spreads. See how the spreading of the sea floor created the Atlantic, Pacific, and Indian oceans. The different colors in the animation represent the age of the ocean floor and the symmetry of sea floor spreading. If you desire, you can also view more detailed animations of the three oceans and how they were formed. || Plate Tectonics: Pangea Continent Maps The Earth was very different 225 million years ago. There was a supercontinent known as Pangaea. This supercontinent broke into many different pieces and those pieces developed into the Earth's continents today.Take a look at the illustrated maps of the Earth on this Web page to get a glimpse of what the Earth looked like many years ago. You will see the progressive changes showing the Earth of the past to the present continents of the Earth today. || Even if you stand perfectly still, the ground beneath you is slowly drifting. The entire continent is like a giant raft that moves about an inch a year. The movement is incredibly slow but the force of something as big as a continent moving an inch is incredibly big. The crust of the Earth is divided into different plates that float on molten magma. When plates scrape against each other, it causes a fault and earthquakes. The collision of these plates can cause rocks to bend as they are pushed upwards into mountains. || What on Earth is the Mid-Ocean Ridge? A professor of marine geophysics discusses the mid-ocean ridge in this article from the NOAA Ocean Explorer. This article provides background information on an expedition near the Galapagos Islands to study sea floor spreading. You will find a description of the mid-ocean ridge system and its length and depth. Learn why the mid-ocean ridge is geographically important and see what happens when plates spread apart. There is discussion about the volcanic eruptions that happen under water and the formation of new sections of earth's crust. ||
 * Building bridges
 * Supercontinents
 * Plate Tectonics
 * Break-up of Pangea
 * Earthforce in the Crust