Earth has gravity because of its mass. Gravity is a fundamental force of nature that exists between any objects with mass. The more massive an object is, the stronger its gravitational pull. Earth's gravity is a result of its mass, which is approximately 5.97 x 10^24 kilograms.
The concept of gravity is described by Albert Einstein's theory of general relativity, which explains how mass and energy curve spacetime, creating what we perceive as gravitational attraction. According to this theory, objects with mass cause a curvature in the fabric of spacetime around them. Other objects moving through this curved spacetime experience a gravitational force pulling them toward the object with mass.
So, in the case of Earth, its mass generates a gravitational field around it. This gravitational field causes objects near Earth's surface to be pulled downward, creating the sensation of gravity. It's the Earth's mass that gives rise to its gravitational pull, rather than its gravity causing it to have a large mass.
It's important to note that while Earth's gravity is significant enough to keep objects on its surface, the strength of gravity diminishes with distance. As you move farther away from Earth, its gravitational pull becomes weaker.