evidence: In 2015, new research gave further weight to this theory, using simulations of planetary orbits in the early solar system as well as newly uncovered differences in the abundance of the element tungsten-182 detected in the Earth and the moon. [...] The moon's gravitational pull may have been key to making Earth a livable planet by moderating the degree of wobble in Earth's axial tilt, which led to a relatively stable climate over billions of years in which life could flourish. [...] The Earth's axis of rotation is tilted about 23.5 degrees in relation to the ecliptic plane, an imaginary disk through Earth's orbit around the sun. This means the Northern and Southern hemispheres point somewhat toward or away from the sun depending on the time of year, varying the amount of solar radiation they receive and causing the seasons.