Earth


 * Earth**



Moon

[|Earth info] To learn more about our Earth's delicate environment and how to save it go to Our Environment

The third planet from the [|Sun], Earth, is the fifth largest with a diameter of 12,756 kilometers (7,928 miles). This rocky object is the densest major planetary body in the [|Solar System]. It also has an unusually large satellite for its size, as Earth's Moon has about a quarter of its diameter. Many astronomers now believe that the Earth was formed from the collision of a Mars-sized protoplanet with the primordial Earth. Much of the protoplanet's core merged with the Earth's own, while the lighter materials of the collision reformed as the Moon (more [|discussion, illustrations, and links]). The gravitational interaction of the Earth with its Moon slows the Earth's rotation by about two milliseconds per century, so that about 900 million years ago, Earth's "year" was comprised of 481 "days" that lasted only 18 hours long.

//[|NASA] -- [|larger image]//

Viewed from space, Earth's classic image is that of a bluish ball with shifting white clouds, the result of an atmosphere actively sustained by its widespread life. Its atmosphere helps to shield its surface from meteors, most of which burn up before they can strike the surface. The atmosphere is composed of mostly nitrogen (78 percent) and oxygen (21 percent), with traces of argon, carbon dioxide, and water. The presence of free oxygen is quite unusual because oxygen is a very reactive gas. Without the constant and massive respiration of plants and phytosynthetic microbes worldwide, oxygen would quickly combine with other elements, and there would be little free oxygen, as has happened on [|Venus] and [|Mars].



//© [|NCAR], [|ESSL]/[|CGD], [|NSF], [|DOE], [|Marika M. Holland], [|Cecilia M. Bitz], [|Bruno Tremblay] -- larger [|2000] and [|2040] animation stills

The rising level of carbon dioxide and other [|greenhouse gases] in Earth's atmosphere is leading to higher surface temperatures and melting ice deposits, such as the loss of Arctic sea ice during its warm summer months after 2040 according to simulation runs of the [|Community Climate System Model] in 2006 (more [|information and animation]).//

The primordial Earth probably had much more carbon dioxide, but virtually all of it has been incorporated into carbonate rocks, dissolved into the oceans, or incorporated into living plants. However, the tiny amount of carbon dioxide still in the atmosphere at any time warms the Earth's average surface temperature by about 35 °C (95 °F) above what it would otherwise be (from a frigid -21 °C/-17 °F to a comfortable 15 °C/59 °F) via the "[|greenhouse effect]." Without this improved retention of solar heat, the oceans would freeze. On the other hand, the activities of Earth's dominant lifeform ([|Homo sapiens sapiens]) have been increasing the level of carbon dioxide in Earth's atmosphere which appears to be promoting a rising trend in global temperatures, melting ice deposits, and rising sea levels (more from the [|IPCC]).

//Although smaller than the// Chicxulub impact //structure that may have contributed to the demise of the Dinosaurs,// Manicouagan//, a 214-million-year-old crater in eastern Canada (Quebec) that has been eroded nearly flat by glaciers, is easily seen from space because of its huge 62-mile (100-km) diameter. It was made by the largest known fragment of an object that also created: the 25-mile (40-km) diameter, Saint Martin crater in western Canada (Manitoba); the 15-mile (25-km) Rochechouart crater in the Massif Central of France; the 9.3 mile (15-km) Obolon' impact structure in the Ukraine; the 5.6-mile (9-km) Red Wing crater in the western U.S.; and possibly also the 7.4 mile (12-km) Wells Creek, Tennessee impact structure and the 2-mile (3-km) Newporte, North Dakota crater -- both in the U.S.// Earth is currently the only planet on which water can exist in liquid form on the surface, and most (71 percent) of the planet's surface is indeed covered with water. The heat-absorbing capacity of Earth's oceans is crucial to keeping the planet's temperature relatively stable. Liquid water is also responsible for most of the erosion and weathering of the Earth's continents, a process that is unique in the Solar System today, although it may have occurred on Mars in the past).


 * //Earth, our home planet, is the only planet in our solar system known to harbor life - life that is incredibly diverse. All of the things we need to survive are provided under a thin layer of atmosphere that separates us from the uninhabitable void of space. Earth is made up of complex, interactive systems that are often unpredictable. Air, water, land, and life - including humans - combine forces to create a constantly changing world that we are striving to understand.

Viewing Earth from the unique perspective of space provides the opportunity to see Earth as a whole. Scientists around the world have discovered many things about our planet by working together and sharing their findings.

Some facts are well known. For instance, Earth is the third planet from the Sun and the fifth largest in the solar system. Earth's diameter is just a few hundred kilometers larger than that of//** Venus//**. The four seasons are a result of Earth's axis of rotation being tilted more than 23 degrees.**//


 * //Earth's land surfaces are also in motion. For example, the North American continent continues to move west over the Pacific Ocean basin, roughly at a rate equal to the growth of our fingernails. Earthquakes result when plates grind past one another, ride up over one another, collide to make mountains, or split and separate. These movements are known as plate tectonics. Developed within the last 30 years, this explanation has unified the results of centuries of study of our planet, long believed to be unmoving.

From the vantage point of space we are able to observe our planet globally, as we do other planets, using similar sensitive instruments to understand the delicate balance among its oceans, air, land, and life.//**