EARTH
(Ksaahkomm)
Visualization of the spinning Earth. NASA/Goddard Space Flight Center Scientific Visualization Studio
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FORMATION Earth is the third planet from the Sun and the largest of the terrestrial (“rocky”) planets. It was formed approximately 4.5 billion years ago from a massive swirling cloud of gasses and dust, called the solar nebula.
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NASA (Adapted from Goddard Media Studios)
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STRUCTURE ATMOSPHERE AND MAGNETOSPHERE The Earth’s basic structure consists of a solid dense core, a semi-liquid mantel and an outer crust. The inner core is about 2500 km in diameter, equaling about one fifth the diameter of the Earth. Surrounding the inner core is an outer core, about 2000 km thick. Decaying radioactive material in the core releases a great deal of heat. At approximately 5000 degrees C, the Earth’s interior temperature is about the same as the surface of the Sun.
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VIsualization of Continental Drift NASA/Goddard Space Flight Center Scientific Visualization Studio
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Heat from the core drives convection plumes in the overlaying mantel. The mantel is liquid or semi-liquid rock, also called magma. Above the mantel lies the Earth’s outer shell of rigid rocky plates. There are seven major plates, which slowly migrate over the Earth, continually reshaping its surface. This is called "continental drift". The rate of movement ranges from 10mm/yr. up to 75mm/yr.
When plates collide. Graphic courtesy of USA National Parks Service
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The boundaries where these plates meet are very geologically active. Interactions between neighbouring plates results in earthquakes, volcanoes, and the formation of mountain ranges and ocean trenches. The San Andreas Fault (the straight line to the right of the mountains in photo) is one such feature, where the Pacific Plate meets the North American Plate. It is 1300 km long and at least 25 km deep.
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San Andreas Fault line, just to the right of the mountains. Image credit: NASA/JPL
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More than two thirds of the Earth’s surface is covered by water. It is the only planet in the solar system with liquid water on its surface, a feature which is closely intertwined with the history of life on Earth. Only 2.5% of the Earth’s water is fresh water, and more than two thirds of fresh water exists in the form of ice locked in glaciers and the polar ice caps. Fresh liquid water is a precious resource, necessary for many of Earth’s life forms.
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Image credit: NASA
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Earth’s atmosphere is about 78% nitrogen and 21% oxygen, with traces of argon, carbon dioxide and other gasses. A layer of ozone in the upper atmosphere blocks most of the ultraviolet radiation from the Sun. Three quarters of the atmosphere lies within 11 km of the Earth's surface.
The atmosphere sustains life and regulates the Earth’s temperature through the heat-retaining “greenhouse effect.” Without the greenhouse effect, the average surface temperature on Earth would likely be around -18 degrees C instead of the current +15 degrees C. This balance is quite sensitive. Small changes in the amount of greenhouse gasses like carbon dioxide and methane can produce large changes in climate, with dire consequences to the Earth’s ecosystems. |
The thin "skin" of the Earth's atmosphere. NASA/Glenn Research Center
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Temperature map of the Earth. Image courtesy of NASA
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The Earth’s climate varies greatly depending on latitude. Local climates can be divided into five major groups (humid tropics, arid, humid middle latitude, continental and polar). Recorded surface temperatures can range from -89 degrees C in Antarctica to +55 degrees C in hot deserts. Local weather is strongly influenced by the distribution of land masses and its topography, the proximity to oceans and ocean currents, the prevailing winds and the amount of solar energy.
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Earth’s magnetic field originates deep in the spinning core from a dynamo process. It is roughly aligned with the Earth’s geographic poles. Historically, this alignment was extremely important in navigation. The exact location of the magnetic poles changes over relatively short time scales (decades) and the north and south poles “flip” over long time scales. The last reversal was about 700,000 years ago. Based on the history of these events, it is possible that we are over-due for another one. |
The Earth's magnetic field and magnetosphere. Image Credit: NASA
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The Earth’s magnetic field extends beyond our atmosphere into space, forming a magnetosphere. The solar wind (charged particles streaming from the Sun) compresses the magnetosphere on the day side of Earth, and extends it into a long tail on the night side. During solar storms, charged particles can follow the magnetic lines through the Earth’s atmosphere, striking and exciting air molecules and causing aurorae (e.g. the Northern Lights). |
Aurora Australis
Image Credit: NASA
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LIFE Earth is the only place in the universe where life is known to exist. Earth is teaming with life. Life can thrive under seemingly impossible conditions- for example, microbial life can be found in rocks 580 meters below the sea floor, under 2600 meters of ocean.
Deoxyribonucleic acid (DNA) is a molecule that contains the biological information necessary for the growth and functioning of all known living things. DNA molecules, together with proteins, fatty acids and carbohydrates are the four essential elements of all known life forms. Living cells formed from these essential elements are capable of reproduction and are the unit building blocks of all known life. |
Image Credit: NASA
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Many scientists believe that life on other planets is plausible or likely. There are several environments within our solar system that appear to be (or have been) capable of supporting life; for example, in the upper atmosphere of Venus, the planet Mars, and in subsurface oceans of some of the moons of Jupiter or Saturn. This does not mean that life exists there- only that it is possible given our current knowledge. Our solar system is only one of billions of planetary systems in the universe, so the list of potential life-supporting environments is long.
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MOON Earth has only one large natural satellite. It is a little more than one quarter the Earth’s diameter. The most accepted theory of its formation is the “giant impact hypothesis”. This idea suggests that a Mars-sized object, “Theia” collided with the Earth during its formative stages, ejecting a large amount of material into space. This material coalesced into the Moon. The “giant impact hypothesis” is supported by the fact that the Moon’s surface has a nearly identical composition to the Earth’s crust.
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The Moon received its first human visitors on July 20, 1969. Image Courtesy of NASA
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MISSIONS Of course, the Earth is the most extensively explored planet in the solar system. It should be remembered that many of Earth’s species, not only humans, explore their environment. The recorded history of human exploration indicates that it was motivated mainly by economic and/or military concerns. Currently, the Earth’s land surface is almost entirely mapped and “explored” by satellite imagery. The ocean floor has been studied only recently, and vast areas of it remain unexplored.