We are now going to deal with the most commonly accepted hypothesis that would answer several questions. Why is the Earth's axis tilted? Why do we have the seasons? Why we have climate differences? Why do we have a moon? Now you will know why.
Many different theories have been put forward for how the Moon formed, but only the Giant impact hypothesis is widely accepted today. The giant impact hypothesis states that the Moon was formed out of the debris left over from a collision between the Earth and a body the size of Mars, approximately four and a half billion years ago. The colliding body is sometimes called Theia, for the mythical Greek Titan who was the mother of Selene, the goddess of the Moon*.
Consequences of the Impact**
The cataclysmic impact between Theia and the proto-Earth, together with its result, the Moon, had some profound effects on Earth and its subsequent history.
a.) The collision knocked the proto-Earth out of its position, producing the tilt in the Earth's axis, which is the cause of the seasons.
b.) The moon's presence also helped stabilize this tilt, which is likely to have smoothed out climatic conditions over the whole course of Earth's history.
c.) When the Moon was first formed, the Moon was closer to Earth than it is today and these forces were more pronounced. Their strength may have triggered the development of Eart's system of tectonic plates.
d.) The Moon's gravitational pull produces the tides in our planet's oceans. By subjecting organisms that lived in tidal zones to daily (or twice-daily) fluctuations in their living conditions, the Moon may have influenced the pace at which life on Earth evolved.
** Robert Dinwiddle, Bite-Size Science. p.67