Nature
Squirrels are familiar to almost everyone. More than 200 squirrel species live all over the world, with the notable exception of Australia.
The tiniest squirrel is the aptly named African pygmy squirrel—only five inches (thirteen centimeters) long from nose to tail. Others reach sizes shocking to those who are only familiar with common tree squirrels. The Indian giant squirrel is three feet (almost a meter) long.
Like other rodents, squirrels have four front teeth that never stop growing so they don't wear down from the constant gnawing. Tree squirrels are the types most commonly recognized, often seen gracefully scampering and leaping from branch to branch. Other species are ground squirrels that live in burrow or tunnel systems, where some hibernate during the winter season.
Ground squirrels eat nuts, leaves, roots, seeds, and other plants. They also catch and eat small animals, such as insects and caterpillars. These small mammals must always be wary of predators because they are tasty morsels with few natural defenses, save flight. Sometimes groups of ground squirrels work together to warn each other of approaching danger with a whistling call.
Tree squirrels are commonly seen everywhere from woodlands to city parks. Though they are terrific climbers, these squirrels do come to the ground in search of fare such as nuts, acorns, berries, and flowers. They also eat bark, eggs, or baby birds. Tree sap is a delicacy to some species.
Geophysics, which studies the physics of the Earth, has led to many significant discoveries about the Earth and its make-up. Seismologic studies of the Earth have uncovered new information about the interior of the Earth that has helped to give credence to plate tectonic theory.
Significant progress was made in the 1960s, and was prompted by a number of discoveries, most notably of the Mid-Atlantic ridge. The most significant paper was the 1962 publication by American geologist Harry Hammond Hess (Robert S. Dietz published the same idea one year earlier in Nature. However, priority belongs to Hess, since he had already distributed an unpublished manuscript of his 1962 article by 1960). Hess suggested that instead of continents moving through oceanic crust (as was suggested by continental drift) that an ocean basin and its adjoining continent moved together on the same crustal unit, or plate. In the same year, Robert R. Coats of the U.S. Geological Survey described the main features of island arc subduction in the Aleutian Islands. His paper, though little-noted (and even ridiculed) at the time, has since been called "seminal" and "prescient". In 1967, W. Jason Morgan proposed that the Earth's surface consists of 12 rigid plates that move relative to each other. Two months later, in 1968, Xavier Le Pichon published a complete model based on 6 major plates with their relative motions.
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