Earth, our home, is the third planet from the sun. It is the only planet known to have an atmosphere containing free oxygen, oceans of liquid water on its surface, and, of course, life.
Earth is the fifth largest of the planets in the solar system — smaller than the four gas giants, Jupiter, Saturn, Uranus and Neptune, but larger than the three other rocky planets, Mercury, Mars and Venus. It has a diameter of roughly 8,000 miles (13,000 kilometers), and is round because gravity pulls matter into a ball, although it is not perfectly round, instead being more of an "oblate spheroid" whose spin causes it to be squashed at its poles and swollen at the equator.
Roughly 71 percent of Earth's surface is covered by water, most of it in the oceans. About a fifth of its atmosphere is made up of oxygen, produced by plants.
Earth's climate has enabled life to evolve on our planet. Life, in turn, has had effects on the climate.
CREDIT: Reto Stöckli, Nazmi El Saleous, and Marit Jentoft-Nilsen, NASA GSFC
CREDIT: Reto Stöckli, Nazmi El Saleous, and Marit Jentoft-Nilsen, NASA GSFC
Earth's climate has enabled life to evolve on our planet. Life, in turn, has had effects on the climate.
CREDIT: Reto Stöckli, Nazmi El Saleous, and Marit Jentoft-Nilsen, NASA GSFC
CREDIT: Reto Stöckli, Nazmi El Saleous, and Marit Jentoft-Nilsen, NASA GSFC
Earth's climate has enabled life to evolve on our planet. Life, in turn, has had effects on the climate.
CREDIT: Reto Stöckli, Nazmi El Saleous, and Marit Jentoft-Nilsen, NASA GSFC
CREDIT: Reto Stöckli, Nazmi El Saleous, and Marit Jentoft-Nilsen, NASA GSFC
The Earth spins on an imaginary line called an axis that runs from the north pole to the south pole, while also orbiting the sun. It takes Earth 24 hours to complete a rotation on its axis, and roughly 365 days to complete an orbit around the sun.
The Earth's axis of rotation is tilted in relation to the ecliptic plane, an imaginary surface through Earth's orbit around the sun. This means the northern and southern hemispheres will sometimes point toward or away from the sun depending on the time of year, varying the amount of light they receive and causing the seasons.
Earth's orbit is not a perfect circle, but is rather an oval-shaped ellipse, like that of the orbits of all the other planets. Earth is a bit closer to the sun in early January and farther away in July, although this variation has a much smaller effect than the heating and cooling caused by the tilt of Earth's axis. Earth happens to lie within the so-called "Goldilocks zone" around its star, where temperatures are just right to maintain liquid water on its surface.
History
Earth probably formed at roughly the same time as the sun and other planets some 4.6 billion years ago, when the solar system coalesced from a giant, rotating cloud of gas and dust known as the solar nebula. As the nebula collapsed because of its gravity, it spun faster and flattened into a disk. Most of the material was pulled toward the center to form the sun. Other particles within the disk collided and stuck together to form ever-larger bodies, including the Earth. The solar wind from the sun was so powerful that it swept away most of the lighter elements, such as hydrogen and helium, from the innermost worlds, rendering Earth and its siblings into small, rocky planets.
Scientists think Earth started off as a waterless mass of rock. Radioactive materials in the rock and increasing pressure deep within the Earth generated enough heat to melt Earth's interior, causing some chemicals to rise to the surface and form water, while others became the gases of the atmosphere. Recent evidence suggests that Earth's crust and oceans may have formed within about 200 million years after the planet had taken shape.
The history of Earth is divided into four eons — starting with the earliest, these are the Hadean, Archean, Proterozoic, and Phanerozoic. The first three eons, which together lasted nearly 4 billion years, are together known as the Precambrian. Evidence for life has bee found in the Archaean about 3.8 billion years ago, but life did not become abundant until the Phanerozoic.
The Phanerozoic is divided into three eras — starting with the earliest, these are the Paleozoic, Mesozoic, and Cenozoic. The Paleozoic Era saw the development of many kinds of animals and plants in the seas and on land, the Mesozoic Era was the age of dinosaurs, and the Cenozoic Era we are in currently is the age of mammals.
Most of the fossils seen in Paleozoic rocks are invertebrate animals lacking backbones, such as corals, mollusks and trilobites. Fish are first found about 450 million years ago, while amphibians appear roughly 380 million years ago. By 300 million years ago, large forests and swamps covered the land, and the earliest fossils of reptiles appear during this period as well.
The Mesozoic saw the ascendence of dinosaurs, although mammals also appear in the fossil record about 200 million years ago. During this time, flowering plants became the dominant plant group and continue to be so today.
The Cenozoic began about 65 million years ago with the end of the age of dinosaurs, which many scientists think was caused by a cosmic impact. Mammals survived to become the dominant land animals of today.
Composition & Structure
- Atmosphere
Air surrounds Earth and becomes thinner farther from the surface. Roughly 100 miles (160 kilometers) above Earth, the air is so thin that satellites can zip through with little resistance. Still, traces of atmosphere can be found as high as 370 miles (600 kilometers) above the surface.
The lowest layer of the atmosphere is known as the troposphere, which is constantly in motion, causing the weather. Sunlight heats the Earth's surface, causing warm air to rise. This air ultimately expands and cools as air pressure decreases, and because this cool air is denser than its surroundings, it then sinks, only to get warmed by the Earth once again.
Above the troposphere, some 30 miles (48 kilometers) above the Earth's surface, is the stratosphere. The still air of the stratosphere contains the ozone layer, which was created when ultraviolet light caused trios of oxygen atoms to bind together into ozone molecules. Ozone prevents most of the sun's harmful ultraviolet radiation from reaching Earth's surface.
Water vapor, carbon dioxide and other gases in the atmosphere trap heat from the sun, warming Earth. Without this so-called "greenhouse effect," Earth would probably be too cold for life to exist, although a runaway greenhouse effect led to the hellish conditions now seen on Venus.
Earth-orbiting satellites have shown that the upper atmosphere actually expands during the day and contracts at night due to heating and cooling.
- Magnetic field
Earth's magnetic field is changing in other ways, too — globally, the magnetic field has weakened 10 percent since the 19th century. These changes are mild compared to what Earth's magnetic field has done in the past — sometimes the field completely flips, with the north and the south poles swapping places.
When charged particles from the sun get trapped in Earth's magnetic field, they smash into air molecules above the magnetic poles, causing them to glow, a phenomenon known as the aurorae, the northern and southern lights.
- Chemical composition
The Earth's core consists mostly of iron and nickel and potentially smaller amounts of lighter elements such as sulfur and oxygen. The mantle is made of iron and magnesium-rich silicate rocks. (The combination of silicon and oxygen is known as silica, and minerals that contain silica are known as silicate minerals.)
- Internal structure
Above the core is Earth's mantle, which is about 1,800 miles (2,900 kilometers) thick. The mantle is not completely stiff, but can flow slowly. Earth's crust floats on the mantle much as a wood floats on water, and the slow motion of rock in the mantle shuffles continents around and causes earthquakes, volcanoes, and the formation of mountain ranges.
Above the mantle, Earth has two kinds of crust. The dry land of the continents consists mostly of granite and other light silicate minerals, while the ocean floors are made up mostly of a dark, dense volcanic rock called basalt. Continental crust averages some 25 miles (40 kilometers) thick, although it can be thinner or thicker in some areas. Oceanic crust is usually only about 5 miles (8 kilometers) thick. Water fills in low areas of the basalt crust to form the world's oceans. Earth has more than enough water to completely fill the ocean basins, and the rest of it spreads onto edges of the continents, areas known as the continental shelf.
Earth gets warmer toward its core. At the bottom of the continental crust, temperatures reach about 1,800 degrees F (1,000 degrees C), increasing about 3 degrees F per mile (1 degrees C per kilometer) below the crust. Geologists think the temperature of Earth's outer core is about 6,700 to 7,800 degrees F (3,700 to 4,300 degrees C), and the inner core may reach 12,600 degrees F (7,000 degrees C), hotter than the surface of the sun. Only the enormous pressures found at the super-hot inner core keep it solid.
Orbit & Rotation
Average Distance from the Sun
English: 92,955,820 miles
Metric: 149,597,890 km
Perihelion (closest)
English: 91,400,000 miles
Metric: 147,100,000 km
Aphelion (farthest)
English: 94,500,000 miles
Metric: 152,100,000 km
Average Length of Solar Day
24 hours
Length of Year
365.24 Earth days
Equatorial Inclination to Orbit
23.45 degrees
(Source: NASA.)
Moon
Earth's moon is 2,159 miles (3,474 kilometers) wide, about one-fourth of Earth's diameter. Earth has one moon, while Mercury and Venus have none and all the other planets in our solar system have two or more.
The leading explanation for how the moon formed was that a giant impact knocked off the raw ingredients for the moon off the primitive molten Earth and into orbit. Scientists have suggested the impactor was roughly 10 percent the mass of Earth, about the size of Mars.
Species Overview
Earth is the only planet in the universe known to possess life. There are several million known species of life, ranging from the bottom of the deepest ocean to a few miles into the atmosphere, and scientists think far more remain to be discovered.
![Earth's Nature gets more and more unbalanced. Soil and oceans are being weakened as buffers against global warming. A down ward spiral with long-term implications for the climate system.
If the seas and the land are less able to soak up or store greenhouse gases, more of these carbon emissions will enter the atmosphere, holding in even more heat from the sun. Studies show a gradual increase in atmospheric carbon dioxide (CO2) over the last half-century has accelerated the release of methane and nitrous oxide in the soil. These gases are respectively 25 and 300 times more effective at trapping radiation than CO2, the principal greenhouse gas by volume. This feedback to our changing atmosphere means that nature is not as efficient in slowing global warming as we previously thought.
Earlier studies examining how additional CO2 affects the capacity of different soils -- in forests, grasslands, wetlands and agricultural fields -- to either absorb or release these two gases yielded conflicting results.
More CO2 increased nitrous oxide in all soils, but soils in rice paddies and wetlands released more methane in particular.
The culprits in both cases are microscopic soil organisms that breathe in CO2 and exhale methane. The more carbon dioxide in the air, the more these single-cell greenhouse-gas factories thrive. The carbon credit that is attributed to faster plant growth driven by extra CO2 in the air must be revised, many scientists say. This credit helps to offset the negative impact of greenhouse gases - but the new data suggests it should be written down by a fifth.
By overlooking the key role of these two greenhouse gases, previous studies may have overestimated the potential of ecosystems to mitigate the greenhouse effect. There is enough evidence that global warming is eroding the ability of the ocean to soak up CO2. Earth's seas take up roughly one-third of all human carbon emissions, but how this sponge responds to rising CO2 levels is a tough question, mainly because data has been spotty geographically and didn't cover long time periods. In the North Atlantic rising air and water temperatures were slowing the pace at which carbon is absorbed across a large portion of this ocean's subtropical zones. The ocean is taking up less carbon because of the warming caused by the carbon in the atmosphere. Up to now, scientists reasoned that only when carbon content in the ocean rose faster than in the atmosphere could one say that the capacity to take in CO2 had diminished.
But the new study shows that the ocean sink can be weakened even without this visible sign. What we are going to see is that the ocean will keep its equilibration the balance between atmospheric and ocean carbon levels] but it doesn't have to take up as much carbon to do it because it's getting warmer at the same time - warmer water cannot hold as much CO2 as colder water. Earth ocean's temperatures are rising, ocean's carbon capacity decreases](http://www.keepbanderabeautiful.org/dust-storm-ii.jpg)
Citizens of all countries have to work together to keep Earth beautiful!
Jauh sebelum ilmu kedokteran maju seperti sekarang, madu telah dipercaya sebagai salah satu 
