Apollo 17 sample of lunar basalt. The dark areas visible on the Moon (the lunar maria) are plains of flood basaltic lava flows. Lunar basalts differ from terrestrial ones in their high iron content and wide range of titanium concentrations. Lunar basalts range from 4.2 to 1.2 billion years old, with most being around 3 to 3.5 billion years old. The Apollo moon landings from 1969 to 1972 returned 2,415 samples and over 380 kilograms of moon rock. Studying moon rock helps reveal the conditions present in the early solar system when the Moon and Earth were forming. This sample has a diameter of 15 millimetres and weighs 1.1 grams.