According to a new study, scientists think Earth's moon formed about 95 million years after the first solids condensed in the solar system. While there are competing theories, most scientists think that in those early days of the solar system Earth was impacted by a huge, Mars-sized body that spewed debris into orbit around the nascent planet.
Eventually, gravity bonded the vaporized debris from Earth's crust together, creating the moon. Earth's moon is the largest in the solar system in relation to its host planet. In theory, the impact that created the moon was so forceful that it left the natural satellite as a hot, liquid blob during its early formation.
As the molten rock cooled, the lunar crust formed, but the baby moon didn't get much of a reprieve from the cosmic action. Between 4.5 billion and 4.3 billion years ago, scientists think that a huge object impacted the moon's south pole, forming the South Pole-Aitken Basin. It is one of the two largest known impact basins in the solar system, and skywatchers can still observe it on the moon's face today.
From about 4.1 billion to 3.8 billion years ago, the solar system experienced what scientists call the Late Heavy Bombardment. Researchers think that the moon and inner planets were pummeled by unknown numbers of asteroids and comets. Because the interior of the moon wasn't completely cooled at this time, magma seeped out through cracks in the lunar surface, according to NASA.
Until about 1 billion years ago, the moon's nearside was volcanic. The dark, basaltic planes called lunar maria. ("seas" in Latin) that can still be seen on the moon's surface were formed by ancient volcanism. The last of the large impacts also probably happened around this time. Eventually the moon cooled, and experienced other, smaller impacts, giving it the pock marked appearance it has today.
Today, anyone looking skyward on a clear night can see the after effects of the moon's evolution on its face. At the moment, the moon is 225,623 miles (363,104 kilometers) from Earth during its closest approach, but the planet's only natural satellite is slowly moving away from Earth. The moon is distancing itself from Earth at a rate of about 1.5 inches (4 cm) every year.
Source :
http://www.space.com/25320-moon-evolution-photo-timeline-gallery.html
