Layers of the Earth

The earth have four layers: the crust, mental, inner core, and outer core. The lithosphere (when divided into parts called plates) is the crust and the upper part of the mental. the lithosphere is about 5 to 30 miles deep, the mental is about 1800 miles thick, the outer core is about 1300 miles thick and the inner core is about 800 miles to the center of the earth.

Major geological features of California

One of the best known sites in California is the Sierra Nevada Mountain range. This mountain range stretches 400 miles from north to south. In the Triassic Period an island ark crashed into the continent of North America. This created a set of mountains. At roughly the same time a subduction zone formed in roughly the same place formed plumes under ground which 0pushed the mountain range up forming the Sierra Nevada batholith.

Another mountain is Mt. Shasta.

 This volcano is formed by subduction. The Pacific Plate subducted and formed this volcano. Eruptions happen usually every 800 to 600 years.

Mid-ocean ridge

Mid-ocean ridge is an underwater mountain range formed by plate tectonics. At mid-ocean ridge, molten material rises from the mantle and erupts. The molten material then spreads out, pushing older rock to both sides of the ridge. As it cools, it forms a strip of solid rock in the center of the ridge. Then more molten material splits apart the strip of solid rock that formed before, pushing it aside. The process, called sea-floor spreading, continually adds new material to the ocean floor. The ocean floor does not just keep spreading. Instead, it sinks beneath deep underwater canyons called deep-ocean trenches. Then subduction takes place. Subduction is the process when the ocean floor sinks beneath a deep-ocean trench and back into the mantle. At deep-ocean trenches, subduction allows part of the ocean floor to sink back into the mantle, over tens of millions of years. This process can change the size and shape of the oceans, and the ocean floor is renewed about every 200 million years.
(the following picture shows the mid-ocean ridge in red, to give you the idea of how big it is. Click on it to make it bigger.)

Ring Of Fire

The Ring Of Fire is the consequence of plate tectonics. The Pacific plate constantly moves around and crash into other plates or submerge into the mantle. This is what causes the volcanoes to form near this area. About 75% of the world's active and dormant volcanoes are located here. Major earthquakes are also located here. The Cascade Volcanic Arc was formed because of the plates. Another example was the Great Kanto Earthquake all the way in Japan. The earthquake was because of direct motion of the plates. Tsunamis are also a danger at the Ring Of Fire. Under sea earthquakes may cause plate monition and also to tsunamis. Sometimes, the plates also slode past each other, causing more earthquakes.

Plate Tectonics

Earth's lithosphere is broken into sections called plates. They fit closely together along cracks in the crust, and so they carry both continents and parts of the ocean floor. They are in constant, slow motion driven by convection currents (Convection currents are circular currents or movement within a liquid or gas due to different densities of the hotter and cooler parts, so the magma move under the surface, pushing the plates) in the mental. The plates float on the top of the atmosphere and spread out beneath the lithosphere, making the movements of Earth's plates. They move about 1 cm per year! As they move, the produce changes in Earth's surface, like volcanoes, mountain ranges, and deep motion trenches. The edges of different plates, where they meet each other, are called plate boundaries. There are three types of plate boundaries - transform boundaries, divergent boundaries, and convergent boundaries.
(the following picture shows the different plates, when you click on it it becomes bigger)

Pangea Evidence

You may be wondering how come people believe in Pangae - the super continent. Well, there was an evidence that led to the discovery by Alfred Wagner - fossils.
Fossils that matched were found on different continents with many miles between them. How is that possible? The climate is very different on these continents. Wagner suggested that these continents may have been close to each other millions of years ago. Also, the continents shape fits together perfectly.
(click on the Pangea picture to see the movement)

Boundaries

Now that you know about plate tectonics, you should learn about boundaries. As you already learned, the crust is divided into many different plates, and the plates move around on the mantel. Sometimes, the mantle is more solid and sometimes it is more watery, the plates move faster when the riding on the more watery mantle and slower when on more solid mantle. The plates move and when plates interact with each other, they form boundaries. There are three types of zones, one of them is the spreading zone, another is fault zone, and the last is converging zone. The spreading zone is mostly found under the sea. These zones are formed when the plates move away from each other. The opening constantly open up and opening into the mantle. When the mantel hardens, new earth is formed, the plates then keep moving apart and keeps on creating new earth.
Another type of boundary is a fault zone. A fault zone is when two plates slide past each other. No new earth is formed, no earth is lost. Sometimes earthquakes occur at these fault zones. The third type of zone is the converging zone.A converging zone is formed when two plates move together. Sometimes, when two plates meet, the denser plate slides down and join the mantle, creating earthquakes and sometimes even volcanoes, but when the plates crash head on, mountains form. That is what happens at the zones.

Pangea, the Super Continent

Did you know that once the continents were all connected? Yes they were. Plate tectonics constantly move the continents around. When the continents move far enough, for long enough, new continents would be formed and this would change a lot. Continents may block the currents of the ocean and make the planet super hot or cause ice ages. Pangea was formed after the super continent, Rodinia broke apart. the plates began moving and by the Permian Period, Pangea was formed. The dinosaurs developed on Pangea, but by the mid Jurassic Period, Pangea split apart into many pieces and carried dinosaurs together with them. The pieces eventually moved to where the continents are today.