is one of those things that you take for granted. There are two points that we take for granted: it is always there and it never changes. If the earth's gravity ever changed, it would produce a serious effect on almost everything that surrounds us, because a lot of things organized around the current state of gravity.
Before considering the implications of gravity changes, let's see what it is. Gravity is the force of attraction between any two atoms. Let's say you take two balls and put them on the table. Between these two balls, or rather between the atoms of which they consist, will of the weak gravitational pull. If you use two massive pieces of lead and precise tools, you can measure this infinitesimal attraction. Only if you have a huge number of atoms collected together — as in the case with planet Earth — gravitational attraction to be significant.
The reason that gravity of the Earth never changes, is that the mass of the Earth never changes. The only way to change the gravity of Earth to change the mass of the planet. A sufficiently large mass change, which could lead to a change in gravity, is not planned.
Could we survive without gravity?
Let's ignore the physics and imagine that one day the planet's gravity will turn off and on the planet Earth will not be the force of gravity. It will be a terrible day. We depend on gravity and things that surround us — cars, other people, furniture, pen on your Desk too. Everything that is not tied to the place, suddenly swim. Will float not only the furniture and the handle, but the atmosphere, the water in the oceans and rivers. This problem is the moon — the satellite of the Earth has insufficient gravity to hold an atmosphere around itself, so the condition around the moon okolovenoznoe. Without an atmosphere of any living creature and you die, and any liquid will evaporate into space.
In other words, if the planet will be deprived of gravity, one will not last long.
If gravity suddenly doubled, it will be too bad because everything will be twice as hard. In any building there will be serious problems. Houses, bridges, skyscrapers, supporting columns and beams, they are designed for normal gravity. Most of the buildings will quickly fall if you increase the load by half. Trees and plants will have problems. At the power lines too. The air pressure will be doubled and will seriously affect the weather.
Now you understand that without the normal gravity we can not do without air and water. This is one of the constants that defines our lives.