You might guess that magma or tumbling rocks fill the void, but the truth is much more prosaic: water. Petroleum deposits, which are naturally mixed with water and gas, lie thousands of feet below the earth’s surface in layers of porous rock, typically sandstone or limestone. (Contrary to what you might imagine, drilling for oil is more like sucking oil from a sponge with a straw than from a giant pool of liquid.)
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.