No one knows for sure why the Earth’s axis is tilted, but many theorize that it was the result of a collision with a large planetoid during the last stages of Earth’s formation over 4.5 billion years ago.
The theory is that the impact with this small, rocky planet not only knocked Earth to a tilt but also tore away a chunk of Earth, forming the moon.
Time and spinning smoothed Earth’s and the moon’s surfaces back into a sphere. Or so the theory goes.
Regardless, this tilt gives Earth the seasonal variations necessary to support the variety of lifefrom plants to animals.