Moon Rocks
In 1972, some of the first moon rocks from the Apollo manned space missions were brought back. Moon rock is a term describing rocks formed on the Moon, and is loosely applied to rocks collected during human exploration. These rocks are measured in radiometric dating techniques. They range from 3.16 billion years for the basaltic samples from Lunar Maria, to about 4.5 billion years old for the rocks in the highlands. Based on dating techniques, the youngest eruptions of basaltic rock are believed to have happened about 1.8 billion years ago. In contrast, the oldest rocks found on Earth are between about 3.8 to 4.16 billion years ago. There are currently 3 sources of Moon rocks. Those from the Apollo missions, rocks collected and returned from the Soviet Luna Missions, and rocks that were ejected naturally by craters forming, and rocks falling down to the Earth's surface. During the six Apollo surface missions, 2,415 rock samples weighing 382kg (842lbs) were collected, the majority by missions 15, 16, and 17. The three lunar space craft returned with an additional .32kg (.7lbs) of samples. Since 1980, 120 lunar meteorites representing 60 different meteor showers (none witnessed) have been collected on Earth, bringing in an additional mass of over 48kg. Lunar rocks are similar to Earth's rocks, with the basic isotope oxygen, but they are completely lacking commonly found minerals on Earth.