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Cave, also called cavern, is a naturally hollow area in the earth that is large enough for a person to enter. Some caves consist of a single chamber only a few yards or meters deep. Other caves are vast networks of passages and chambers. The longest cave ever explored is the Mammoth-Flint Ridge cave system in Kentucky. This cave has about 340 miles (550 kilometers) of explored and mapped passageways, but geologists think that it extends even farther. More »
Artesian well, ahr TEE zhuhn, is a well that taps ground water which is under pressure. Such... More >>
Centrosphere is the inner core of the earth. It is also called the barysphere. Its diameter is... More >>
Hydrosphere. When we think of the earth, we think mostly of areas of land. However, the land... More >>
Mineral water, also called aerated water, is spring water that has a high content of mineral... More >>
Plate tectonics is a theory that explains the origin of most of the major features of Earth's... More >>
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