Unique Earth

EARTH
As far as science knows the planet earth is unique in the entire universe. Certainly this is true in our own solar system. Earth is far better suited for life than any other planet, yet even here most of the environments are too hot, too cold, too far underground or too far above ground to support much life. In the many thousands of miles of changing environments from the center of the earth to the edge of its atmosphere, there are only a few meters of habitable environment for most life forms, and therefore, almost all creatures are forced to live there. Although in our solar system only the earth was made to be inhabited , even on the earth only a thin slice is ideally suited for most life-forms
The miracle of Air
The mixture of gases usually found in the atmosphere not contaminated by human pollution is perfect for life. If it were much different (e.g. 17 percent instead of 21 percent oxygen, too little carbon dioxide, etc., or the atmospheric pressure were much higher or lower), life would cease to exist on earth.

The Miracle of Water
The earth is the only known planet with huge bodies of water. Seventy percent of its surface area consists of oceans, lakes, and seas surrounding huge bodies of land. The few other planets that have water contain only moisture floating as vapor on their surface or small amounts of ice or liquid water on the planet itself, not large bodies of liquid water as on earth.
Water is unique in that it can absorb enormous amounts of heat without a large alteration in its temperature. Its heat absorption level is about ten times as great as steel. During the day, the earth's bodies of water rapidly soak up enormous amounts of heat; thus, the earth stays fairly cool. At night, they release the vast amounts of heat that they absorbed during the day, which, combined with atmospheric effects, keeps most of the surface from freezing solid at night. If it were not for the tremendous amounts of water on the earth, far greater day and night temperature variations would exist. Many parts of the surface would be hot enough to boil water during the day, and the same parts would be cold enough to freeze water at night. Because water is an excellent temperature stabilizer, the large oceans on earth are vital for life to exist on earth.
Rotation,Revolution, Sun and Moon
If the moon was much larger or nearer to the earth, the huge tides that would result would overflow onto the lowlands and erode the mountains. If the continents were leveled, it is estimated that water would cover the entire surface to the depth of over a mile! If the earth was not tilted 23° on its axis, but rather was on a 90° angle in reference to the sun, we would not have four seasons.
Without seasons, life would soon not be able to exist on earth—the poles would lie in eternal twilight, and water vapor from the oceans would be carried by the wind towards both the north and south, freezing when it moved close enough to the poles. In time, huge continents of snow and ice would pile up in the polar regions, leaving most of the earth a dry desert. The oceans would eventually disappear, and rainfall would cease. The accumulated weight of ice at the poles would cause the equator to bulge, and, as a result, the earth's rotation would drastically change.
Gravity
Tides
The Earth's tides are caused by the moon's gravititional pull on the oceans. Tides are the rise and fall of the ocean level as related to the shoreline which occurs over every 12 hours or so.
To a lesser degree the moon also pulls on the rivers, lakes and land. Find out more about tides by clicking here .
Flight
Flying has been done by birds for millions of years. Yet flight is still an amazing science; the ability to break away from gravity - or at least it appears that way. For birds it is all about the structure of their bones, wings and feathers. For humans that don't have those structural positives, we have to design machinery that mimics the science that allows a bird to fly.
Airplane wings are designed after bird wings with a special curve in an effort for air to "lift" the plane. As a wing moves through the air, the curve of the top of the wing speeds up the air as it flows across. This reduces the pressure of the air over the top of the wing. Air on the underside then pushes upward. This is known as the Bernoulli's Principle, for the famous scientist Daniel Bernoulli, who determined that the higher the velocity of a liquid, the lower the pressure it exerts. This also applies to air and is what allows kites, airplanes, space shuttles, and even plastic discs to fly. It helps fans blow air and propellers to push boats through the water.
Floating on Water?
When an object floats on the top of water, gravity is still in play. For an object to float, it must displace enough water to make up the same mass as the object itself. Once that happens, the remaining mass then sits on top of the water. For example: if a boat has a mass of 45 grams, it will displace 45 grams of water and if that has happened before the whole thing has sunk below the surface level of the water, the boat floats