How Does Gravity Affect the Earth?
An important effect of gravity on the Earth is that the sun's gravity is responsible for the Earth's regular orbit through the solar system. The Earth travels at a velocity that approximates the force the sun exerts on the planet, resulting in a regular orbit. Without gravity, the planet would spin away into space, and if gravity was suddenly increased, it would eventually spiral into the star's fiery surface.
Gravity is responsible for the rising and falling of the tides. Water in the ocean is pulled down by the Earth's gravity, but when the moon is overhead, the satellite's own gravitational pull neutralizes some of that force. This allows the water to rise on that side of the planet, creating a high tide. The centrifugal force created as the moon and Earth rotate around a central point also causes a high tide on the opposite side of the planet.
Gravity played a role in the formation of Earth and its current level of tectonic activity. As the planet formed, denser elements were drawn down into the protoplanet's core. This included heavy elements, such as iron and nickel, and radiation sources, such as uranium and plutonium. Over time, these radioactive materials decayed in the core, keeping it molten and allowing the upper layers of the Earth's crust to float over a sea of liquid magma.