Question

what is the reason for gravitation in earth

Answer 1

I guess you are asking how mass causes gravitation?

Answer 2

According to newton's law of gravitation, every body gets attracted to every other body with a force proportional to the product of their mass and inversely proportional to the square of the distance between them.But gravitational force is only attractive since mass cannot be negative

Answer 3

the reason for gravitation is due to ' interaction between masses by the medium of an exchange particle called graviton '. a graviton has zero rest mass and travels at the speed of light. this is the simplest explanation one can give. if you want in depth explanation, you have to wait till your post graduate study in physics