Transcript Now
The Moving Crust Based on Discover God’s Creation, ch. 3-1, 3-2 & 3-3 3-1 Continental Drift • As people explored Earth more thoroughly, they discovered new facts that showed that Earth had changed over thousands of years. • As the “new world” was discovered and maps were drawn more accurately, it looked as if the edges of some continents fit together like a jigsaw puzzle. We are not sure when or over how many years this happened, or what started the process. Pangea • 1800— Alexander Von Humboldt found mountains in South America that matched mountains in Africa. Humboldt believed that the continents had been separated by erosion. • By 1912, Alfred Wegener, a German scientist, suggested that long ago the continents were joined in a large landmass. • He called this landmass “PANGEA”. It appeared that Pangea split into what we now call continents. Once split, they slowly drifted to where they are today. Continental Drift Theory Wegner based his theory on several ideas: 1. The coastlines and mountains of Africa and South America looked as if they fit together like a jigsaw puzzle. 2. Fossils found on the African continent matched those found in South America. 3. Tropical plants were found frozen in the ice of Antarctica. Although Wegner had these observations, he could not explain how or why these sections had split and drifted apart. 3-2 Sea-Floor Spread • Sonar came into use during WWII as a device to locate submarines. • Sonar transmits sound waves that bounce off objects. By recording the time it takes sound waves to travel out and bounce back, how far away an object is can be measured. • This has allowed geologists to draw more accurate maps of the ocean floor. • Today, use is being made of space satellites. • In spite of this, much of the ocean floor is unexplored. Ocean Floor Features As geologists charted the ocean floor, they discovered new features. • Trenches: long, narrow canyons in the deepest parts of the ocean • Midocean Ridge: a large underwater mountain range that circles earth. Ocean Floor Features As geologists charted the ocean floor, they discovered new features. • Rift Valley: a narrow valley running down the Midocean Ridge. This area is warmer than the surrounding areas. • Pillow Lava: formed when molten rock cools underwater. Found in the rift valley. Sea-Floor Spread • This theory says that magma from the mantle of the earth pushes up and out at the rift valley. • This upward movement of the magma causes the sea floor on either side to spread out. • As the magma pushes out, it pushes the sea floor apart on either side and forms new ocean floor. • This continuing process causes the continents to move farther apart. Sea-Floor Spread Ring of Fire • The theory of sea-floor spread explained how continents could have moved, but not WHY. • When geologists began to mark maps where earthquakes occurred and volcanoes were located, they discovered a pattern. • One of the patterns was named the “Ring of Fire”. The Ring of Fire circles the Pacific Ocean. • It is a place of intense volcanic and earthquake activity. • These patterns show that the earth is divided into sections, or plates. Plate Tectonics According to the plate tectonic theory, the Earth’s crust is broken into seven major plates, each a different size and thickness. These plates “float” on Earth’s liquid mantle. They are often named for the continents they support. Plate Tectonics • At the Midocean ridge, the plates move apart about 1-2 inches a year. This is caused by two forces. • The first, convection currents, is created by the motion of liquids and gases. As a liquid or gas is heated, it rises, as it cools, it sinks. • Geologists believe convection currents occur inside Earth. • These currents cause magma to rise at the midocean ridge and push the plates apart. Plate Tectonics • The second force thought to move plates is plumes. • Plumes are columns of hot magma that rise from the mantle. • As a plume rises, it spreads out below the plate, cools, “locks” onto the plate, and pulls the plate along as it continues to move. • If a plume breaks through the crust, it forms a volcano. Plate Tectonics • As the plate continues to move because of the action of the plume, the volcano stops erupting. • Geologists believe that the Hawaiian Islands were formed in this way. Plate Tectonics Boundaries • Where the edges of the plates come together, they form three kinds of boundaries: • spreading • sliding • colliding Plate Tectonics Boundaries SPREADING BOUNDARIES • These boundaries are often identified by large, spreading valleys. • The Great Rift Valley of northeastern Africa, like the valley in the midocean ridge, is formed as two plates are pushed apart by the upward movement of magma. Great Rift Valley, Kenya, Africa Plate Tectonics Boundaries COLLIDING BOUNDARIES • Colliding boundaries occur where two continental plates collide. • Mountain ranges such as the Himalayas in Asia are formed in this way. • When a continental plate collides with an oceanic plate, the heavy continental plate slips below the lighter oceanic plate. • The continental plate melts and is absorbed back into the mantle. • Ocean trenches and volcanoes occur in these areas. • The Andes are volcanic mountains formed where a continental plate sinks below and oceanic plate. Himalayas Plate Tectonics Boundaries SLIDING BOUNDARIES • Sliding boundaries occur where plates slide past each other. • Instead of sliding smoothly, the plates pull on each other, causing tension to build up. • When the plates slip suddenly, this tension is released in an earthquake. • An example is the San Andreas fault in California. San Andreas Fault, California • The earth is not solid and unmoving. • Just as the tides in the ocean rise and fall each day, the continents rise and fall each day as much as six inches. • Creationist viewpoint: The earth has many evidences of catastrophes. It is possible that in God’s original creation, there was only one huge continent. Because of sin, all of creation began to change. • The Bible mentions a gigantic flood, including such forces as the “breakup of the deep”, and “huge winds”. It also mentions a man named Peleg, and tells us that “in his day, the earth was divided”. We can only speculate on how this event changed the surface of the earth.