Week 4

Week 4 marked the start of the second part of our course, which deals with the geology of the earth.

The formation of the earth and much of our universe is believed to be due to an event many millions of years ago called the Big Bang. This theory is the most prevailing one currently as a model for the formation of our universe.

According to this theory, about 14 billion years ago, the entire Universe was very, very small and very, very dense and hot. After that it exploded, and as it expanded it cooled down. It continues to expand to this very day.

The matter condensed into dust, and once this dust and matter particles settled they stuck together forming many of the interstellar bodies around us now, including the planet earth.

While it is true that we cannot study the Earth’s core using visible light, we can study it using other senses. The most important thing we use to sense the Earth’s core are seismic waves. A lot of evidence has lead geologists to believe that the Earth is made of four distinct layers.

These layers are the crust, the mantle, the outer core, and the inner core.

The Earth’s Crust

The first layer consists of about 10 miles (16km) of rock and loose materials scientists call the crust. Underneath the continents, the crust is almost three times as thick as it is under the oceans.

The Earth’s Mantle

Traveling beyond the Earth’s crust, we next encounter the mantle. The mantle extends to a depth of approximately 1,800 miles (2897km), and is made of a thick, solid, rocky substance that represents about 85% of the total weight and mass of the Earth.

The first 50 miles (80km) of the mantle are believed to consist of very hard, rigid rock. The next 150 miles (241km) or so are believed to be super-heated solid rock that due to the heat energy is very weak. Below that for the next several hundred miles, the Earth's mantle is believed to once again be made up of very solid and sturdy rock materials.

The Earth’s Outer Core

Traveling still deeper within the Earth, we next would encounter the Earth’s outer core, which extends to a depth of around 3000 mile (4828km) beneath the surface. It is believed that this outer core is made up of super-heated liquid molten lava. This lava is believed to be mostly iron and nickel.

The Earth’s Inner Core

Finally, we would reach the Earth’s inner core. The inner core extends another 900 miles (1448km) toward the center of the Earth. It is believed that this inner core is a solid ball of mostly iron and nickel.

The earth’s surface is not as fixed as we think it is, instead it has a lot of geological activity occurring all the time.

Plate tectonics is a relatively new theory and it wasn't until the 1960's that geologists, had started to develop it with the help of ocean surveys. Also, the theory that was proposed saying that continents can drift about is called the continental drift theory.

The Earth's surface is made up of a series of large plates.

These plates are in constant motion travelling at a few centimetres per year. The ocean floors are continually moving as well, spreading from the centre and sinking at the edges.

The edges of these plates, where they move against each other, are sites of intense geologic activity, such as earthquakes, volcanoes, and mountain building.

Plate Boundaries are the edge of the tectonic plates.There are three different plate boundaries convergent, divergent, and transform.

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