Chemistry- Earth, its structure and atmosphere

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Changes in the Earth and Its Atmosphere:

By Monisah Mehrban

An Introduction to the Earth:

The Earth is 4.54 billion years old. The Earth's diameter is 12,742 km and the Earth's radius is 6,371 km.

What is the Earth like inside?

The Earth has 3 main layers, which are the following (starting with the outermost):

1. 2. The Crust is relatively thin and rocky. The crust is the outer layer of the earth and is on top of the mantle. It is between 6 and 48 kilometres thick and includes the continents and the ocean floor. The crust is the solid rock layer upon which we live. There are 2  different types of crust:- continental crust, which carries land and oceanic crust, which carries water.

1. The Mantle is a zone of hot rock in the interior of the Earth, which is located between the outer crust and the molten core. The mantle has the properties of a solid but can flow very slowly. The mantle is the widest section of the Earth. It has a thickness of approximately 2,900 km. The mantle is made up of semi-molten rock called magma. In the upper parts of the mantle the rock is hard, but lower down the rock is soft and beginning to melt.

1. The Core is the innermost part of the Earth. It is made from liquid nickel and iron. There is the inner core and the outer core. The inner core is in the centre and is the hottest part of the Earth. It is solid and made up of iron and nickel with temperatures of up to 5,500°C. With its immense heat energy, the inner core is like the engine room of the Earth. The outer core is the layer surrounding the inner core. It is a liquid layer, also made up of iron and nickel. It is still extremely hot, with temperatures similar to the inner core.

Plate Tectonics and Continental Drift:

Continental drift is the process that makes the Earth's plate's move. The Earth's crust and the upper part of the mantles are cracked into a number of large pieces called tectonic plates[1]. These are constantly moving at a few centimetres each year. Although this doesn't sound like very much, over millions of years the movement allows whole continents to shift thousands of kilometres apart. This process is called continental drift. The plates move because of convection currents in the Earth’s mantle.

Convection currents within the Earth's mantle driven by heat released by natural radioactive processes cause the plates to move at relative speeds of a few centimetres per year. Where tectonic plates meet, the Earth's crust becomes unstable as the plates push against each other, or ride under or over each other. Earthquakes and volcanic eruptions happen at the boundaries between plates, and the crust may ‘crumple’ to form mountain ranges.

Wegener's Theory of Continental Drift:

Before Wegener:

The theory of plate tectonics and continental drift was proposed at the beginning of the last century by a German scientist, Alfred Wegener. Before Wegener developed his theory, it was thought that mountains formed because the Earth was cooling down, and in doing so contracted. This was believed to form wrinkles, or mountains, in the Earth’s crust. If the idea was correct, however, mountains would be spread evenly over the Earth's surface. We know this is not the case.

Wegener’s theory:

Wegener suggested that mountains were formed when the edge of a drifting continent collided with another, causing it to crumple and fold. For example, the Himalayas were formed when India came into contact with Asia. Alfred Wegener proposed the theory of continental drift at the beginning of the 20th century. His idea was that the Earth's continents were once joined together, but gradually moved apart over millions of years. It offered an explanation of the existence of similar fossils and rocks on continents that are far apart from each other. But it took a long time for the idea to become accepted by other scientists.

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Alfred Wegener (1880 - 1930)

Wegener's evidence for continental drift was that:

* the same types of fossilised animals and plants are found in South America and Africa

* the shape of the east coast of South America fits the west coast of Africa, like pieces in a jigsaw puzzle

* matching rock formations and mountain chains are found in South America and Africa

Why wasn't Wegener's theory not accepted for million of years.....?

It took more than 50 years for Wegener’s theory to ...

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