Twenty-five years ago today men walked on the moon for the first time. It was an epochal event in human history that produced a rich harvest of scientific knowledge.
Neil A. Armstrong, Edwin "Buzz" Aldrin and the 10 astronauts who followed them during the Apollo program brought back a total of about 840 lbs. of lunar soil and rocks. The material recovered from those missions helped settle many basic questions about the moon's origin, its composition and even the early conditions that affected life on Earth.
One puzzle the Apollo missions helped solve was the origin of the moon. The samples suggested the moon is about 4.5 billion years old, or about the same age as Earth. Yet before Apollo, scientists could only guess as to the chemical composition of the moon. Having no clear idea of what the moon was made of, it was difficult to choose between competing scenarios for the moon's origin and evolution.
One theory held that the moon was originally an independent body that was captured by Earth's gravity sometime in the distant past. Another view suggested that the early Earth was spinning so rapidly that a piece of it broke off and became the moon. A third view -- the so-called "double planet hypothesis" -- suggested that Earth and the moon accreted at about the same time from the cloud of dust and gas that swirled around the Sun during the period of planet formation.
In 1984, 12 years after the Apollo program ended, a group of scientists gathered to review all the evidence gathered during the lunar landings. What emerged was a startling hypothesis -- that the moon was created by a cataclysmic collision of a Mars-sized planetoid with the early Earth. The impact flung a shower of debris into orbit that eventually coalesced into the moon. (The idea actually was first proposed in 1946 by geologist Reginald A. Daly, but it was ignored by the scientific community.) To everyone's amazement, the collision theory fit the new facts revealed by the lunar rocks better than any of its competitors.
Today the collision theory of the moon's origin is widely accepted among astronomers. Moreover, further analysis also showed that the period of intense cratering on the moon which occurred between 4.4 and 3.9 billion years ago may have affected early life on Earth as well. It now appears that the earliest terrestrial organisms began developing some 200 million years after the period of cratering ended -- an excellent example of how much can be learned about Earth by studying the moon. It is a tribute to the vision of its creators that without the Apollo program, none of these discoveries could have been made.