*** How heavy is earth? - approximately 6,000,000,000,000,000,000,000,000 (6E+24) kilograms.
It is "more proper" to ask about mass rather than weight because weight is a force that requires a gravitational field to determine. To weigh the Earth, we would need to know in which object's (for instance the sun or Jupiter) gravitational field we want to calculate the weight. The mass of the Earth, on the other hand, is a constant.
E.g. your mass will always be constant, but you will weigh less on the moon, due to the weak gravity.
*** Do we actually know that for sure or just roughly extimate? - The measurement of the planet's weight is derived from the gravitational attraction that the Earth has for objects near it.
The following equation expresses the gravitational attraction that two spherical objects have on one another:
F = G * M1 * M2 / R2
R is the distance separating the two objects.
G is a constant that is 6.67259x10-11m3/s2 kg.
M1 and M2 are the two masses that are attracting each other.
F is the force of attraction between them.
Assume that Earth is one of the masses (M1) and a 1-kg sphere is the other (M2). The force between them is 9.8 kg*m/s2 -- we can calculate this force by dropping the 1-kg sphere and measuring the acceleration that the Earth's gravitational field applies to it (9.8 m/s2).
The radius of the Earth is 6,400,000 meters (6,999,125 yards). If you plug all of these values in and solve for M1, you find that the mass of the Earth is 6,000,000,000,000,000,000,000,000 kilograms (6E+24 kilograms / 1.3E+25 pounds).
*** How heavy is the moon? - Using the above method about 81 billion tons or 1/81 of the Earth's mass.
*** How much weight can earth actually take if we where to built mass and mass of weight on land to earth would earth break... tiritate or fall - We can build as much as we want. The damage would be to the earths crust and tectonic plate, not the earth's path (orbit) around the sun.
*** What if we went to live on the moon and bring and built home sand, would the moon feel heavier? - The moon's mass would increase. With the moon's mass already 81 billion tons, there have to be considerable increase to affect the moon's weight (gravitational field and orbit around the earth).
*** Is it posible that universe fall from no air into air comming in oneday someday or no way there will be air around the unvierse oneday either - In other words: Is it a possibility that some day the universe will collapse back onto itself? (aka The Big Crunch Theory). It depends on whether there is enough mass in the universe to keep it together. At the moment there is not enough mass that has been seen or inferred, so the answer of today would be that the universe will probably never collapse back on itself. But, we could still find the extra matter, maybe. Many are looking for it.