Theia is named for the Greek goddess of light, daughter of Gaia (Earth) and Uranus (sky), and mother of the sun, moon and dawn. According to this theory, the Earth had no tilt before Theia’s impact.

Seasonal changes result from Earth’s tilt, not its varying distance from the Sun. This tilt determines the intensity of sunlight and length of days in each hemisphere.

The study included data from 1993 through 2010, and showed that the pumping of as much as 2,150 gigatons of groundwater has caused a change in the Earth’s tilt of roughly 31.5 inches.