Structure and Atmosphere
The Earth's interior is made up of:1. The Crust: this is the outermost layer of the Earth 30-50 km (20-30 mi) thick under the continents and 5-10 km (3-6 mi) under the oceans.
2. The Mantle: a layer of denser (melted, not solid) rock about 2900 km (1800 mi) thick
3. The Core: made up of an outer fluid layer and a solid inner region.
The crust is mainly formed by minerals forming rocks chemically linked to oxygen and other elements. Silicates are the most common form of rock found on the Earth's surface. Quartz is the most common form of silicate mineral, and other abundant minerals are combinations of sodium, calcium, and aluminum with silicates. Igneous rocks form when volcanic lava or magma cools and solidifies. Sedimentary rocks are accumulation of rock fragments. Fossils are only found in sedimentary rocks. Metamorphic rocks are igneous or sedimentary rocks that have undergone some transformation caused by long time exposure to high temperature, pressure, impact or any combination of the three. The Stone Mountain in Atlanta is an example of a metamorphic rock.
Hot springs, volcanoes and the high temperature inside mines tell us that the Earth's interior is hot. The increment of temperature as we travel towards the centre of the Earth is steeper near the crust, and eventually levels off several kilometres inside the mantle. The heat of the Earth originates from radioactive decay of minerals and from the heat transported from the centre of the Earth through conduction.
Plate tectonics is the study of rigid lithospheric plates floating on the upper mantle. The heat transportation mechanism or convection of the mantle creates the necessary forces responsible for the movement of plates on which ride the continents. These plates can collide with each other forming orographic regions such as the Himalayas, they can also cause ocean trenches, volcanic islands, and mountain ranges to form, if they move away from each other, rifts occur. In the ocean this process is called sea floor spreading, and on land rift valleys are formed. When two plates slide past each other, there are faults. The boundaries of these plates are regions of large seismic and volcanic activity. Plate tectonic activities produce very visible effects on the Earth's crust, features such as volcanoes and earthquakes exist mainly along the plate boundaries. Most moons and some planets have many impact craters , however these are rare features on Earth. Geologists and planetary astronomers look for similar features in other planets in an effort to gain further understanding of how Earth came to be.
The atmosphere is the nearly transparent envelope of gases and
suspended particles that surrounds the Earth, profoundly influencing
environmental conditions on the planet's surface. Without chemical
processes involving several of the atmospheric gases, life could not
exist. The Earth's atmosphere is made up of particles and gasses with
about 99% of the atmosphere made up of oxygen and nitrogen and about
1% made up of inert gas argon. Particle content and the presence of
other atmospheric gases change continuously and is a very small
fraction of the atmospheric content. The content of the
Earth's atmosphere has changed throughout the eons. Indeed,
much of the present atmosphere came from within the Earth's
interior. Continuous chemical processes are the main agents
that cause the atmosphere content to change. Some of these
processes are dissolution of gases such as CO2
(carbon dioxide) in the ocean and inland water masses and living
organism processing such as plant photosynthesis and anaerobic
activity of simple organisms such as bacteria.
The elements that make up the atmosphere absorb the electromagnetic radiation that we receive from space (including the doses that we receive from the Sun.) Some atmospheric agents are opaque to some part of the spectrum, these agents either absorb this energy or reflect it back into space. For this reason, not all radiation from space reaches the surface of the Earth. A very important and vital energy filter is the ozone layer high in the Earth's atmosphere. The ozone layer absorbs the ultraviolet (UV) radiation coming from the Sun. The UV radiation is responsible for the suntan we get when we go to the beach. The troposphere is the bottom most part of the atmosphere, this is the layer that gives us life as we know it. The stratosphere follows, and higher up we find the mesosphere. The thermosphere is the upper most part of the atmosphere.
Atmospheric Anatomy Meteorologists usually divide the atmosphere into four layers. In order of increasing elevations these are the Troposphere, Stratosphere, Mesosphere, and Thermosphere. Each has a different temperature range. Temperatures decrease with altitude in the troposphere and mesosphere and increases with altitude in the stratosphere and the thermosphere. The troposphere and stratosphere are separated by the tropopause, a level of minimum temperature that varies in altitude from about 16 km (10 mi) near the equator to 9 km (6 mi) near the poles. The stratosphere and mesosphere are separated by the stratopause, a level of temperature maximum that occurs near 50 km (30 mi). The mesosphere and the thermosphere are in turn separated by a temperature minimum, the mesopause, near 80 km (50 mi).
The outermost portion of the atmosphere, at altitudes beyond 450-600 km (280-380 mi), is called the exosphere. Atmospheric atoms in this region readily escape into space after colliding with one another. Helium is the most abundant exospheric gas. The temperature there is approximately 700°C (1300°F) but can vary from 300°C (570°F) during sunspot minimum to 1700°C (3100°F) at sunspot maximum. About 35% of the energy we receive from the sun is reflected back to space by the Earth's crust and the atmosphere. About 15% of the total energy is absorbed by the atmosphere, and about 50% is directly absorbed by the ground. Part of the energy reflected by the Earth is further absorbed by the atmosphere which in turn reflects the same energy in all directions including towards the ground itself. The effect is that the atmosphere and the ground in general get warmed until equilibrium is reached. This effect is known as "the green house effect."
Atmospheric pressure is the result of the collision that takes place between atmospheric components and the ground and everything on top of the ground. Since the bottom layers of the atmosphere support the upper layers of the atmosphere, the atmospheric pressure is greater at the lowermost layer or the troposphere, which is the layer that we live in. On the other hand, higher up in the atmosphere the pressure decreases, and this is proportional to air resistance to movement. For this reason aeroplanes do fly high up in the atmosphere, and as a general rule of thumb, the faster the aeroplane flies, the higher up in the atmosphere the aeroplane has to fly.
Winds are the cause of the unequal heating of the Earth's surface. The convective motion of atmospheric air causes the masses of air to move from latitude to another latitude. The Earth's rotation provides the atmosphere with the necessary energy to complete the job of global wind circulation. The coriolis effect is responsible for large air movement organisation such as hurricanes. In general, air flows from high pressure zones to low pressure zones. Air flowing into a low pressure zone flows counter clockwise in the Northern hemisphere (cyclonic motion), while the opposite happens in the Southern hemisphere (anticyclonic motion).
