11.   Both the earlier extinctions are marked in geologic formations by the sudden disappearance of species that had been common on the Earth.

12.   Groundwater is contained in underground geologic formations called aquifers, which are constantly replenished by rainwater that percolates downward through the soil.

13.   Inject it into geologic formations under the ocean.

14.   Oswald says seismographic studies have indicated Windsor Castle could be sitting on a perfect geologic formation to hold oil or natural gas.

15.   Scientists picked this spot because it is thought to be on the edge of two different geologic formations.

16.   Made of rocks and ice, it has a variety of geologic formations similar to Earth with mountains, craters and basins.

17.   Made of rocks and ice, it has a variety of geologic formations similar to Earth, including mountains and craters.