The regular daily and monthly rhythms of Earth's
only natural satellite,
the Moon, have guided timekeepers for thousands of years. Its influence
on Earth's cycles, notably tides, has also been charted by many cultures
in many ages. More than 70 spacecraft have been sent to the Moon;
12 astronauts have walked upon its surface and brought back 382 kg (842 pounds) of
lunar rock and soil to Earth.
The presence of the Moon stabilizes Earth's wobble. This has led to a
much more stable climate over billions of years, which may have affected
the course of the development and growth of life on Earth.
How did the Moon come to be? The leading theory is that a Mars-sized
body once hit Earth and the resulting debris (from both Earth and the
impacting body) accumulated to form the Moon. Scientists believe that
the Moon was formed approximately 4.5 billion years ago (the age of
the oldest collected lunar rocks). When the Moon formed, its outer
layers melted under very high temperatures, forming the lunar crust,
probably from a global "magma ocean."
Read More About Earth's Moon