Gravity
Because it has sufficient gravity and a strong magnetosphere.
no
There is no simple relationship, but the general tendency is that more massive planets have more gravitational attraction, and are able to maintain a denser atmosphere. The amount of atmosphere a planet has may also depend on it closeness to the Sun / to the planet's star, and to its evolutionary history.
There is no simple relationship, but the general tendency is that more massive planets have more gravitational attraction, and are able to maintain a denser atmosphere. The amount of atmosphere a planet has may also depend on it closeness to the Sun / to the planet's star, and to its evolutionary history.
Life. One reason for this is the fact that it has water and a breathable atmosphere.
It the earth was half its mass, then it might only be able to hold half the atmosphere. In this case, it may not be able to maintain many species of life as we know it.
Well to maintain the oxygen in the earth atmosphere you need to make sure that the level of global warming is decreasing and less fumes will be able to make up the ozone layer. With a thinner layer around the earth this means that oxygen will be able to enter and exit the earths surface, allowing oxygen to still stay in the atmosphere.
Mars has a thinner atmosphere than earth but currently it's still able to have storm systems like wind and dust storms. Mars may have had an atmosphere as dense as Earth's at one time. On November 21, 2008, however, researchers announced new evidence that the atmosphere of Mars was and is still being stripped away by the Solar Wind.
Mercury is the only major planet without an atmosphere. It is able to hold some gases close to its surface, but not really enough to call it an atmosphere. Its due to the size of the planet being so small and lack of a decent magnetic field that it is unable to sustain an atmosphere.
earth
Because, the planet it's self is able to produce it's own oxygen. The atmosphere of the planet, is what makes that planet able to produce it's own oxygen, even if there is no air in space, the atmosphere itself, is able to sustain it's own air. (I think)
able