Planet Earth Surface Life Tropics Seasons Crust and More
About the planet Earth, its surface and crust variations, life on earth, tropics of cancer and capricorn, seasons and lakes.
ANATOMY OF EARTH
Earth's surface is constantly gaining weight through a steady dustfall of cosmic or micrometeoritic particles, an estimated 92,500 particles per second, some 8 billion each 24 hours, a ton or perhaps even 10 tons per day. "Shooting stars," we call these heavenly visitors when we chance to see their swift, gay splendor at night. When they encounter the earth's atmosphere, their temperature shoots upward from the--460deg F. of outer space to more than 2,000deg F. Raindrops need these dust particles to form around.
Up from earth's interior comes further building material, magma turning into lava as it wells through the mouths of volcanoes. Kilauea, on Hawaii, has been putting out steadily since 1969--producing 300,000 cubic yards of scenic lava per day.
Life on earth dwells strictly between water's boiling and freezing points. Vatnajokull, Iceland's great glacier, has a volcano, Hvannadalshnjukur, sticking out of its south face--a dramatic confrontation between ice and fire. Yellowstone National Park has over 3,000 hot springs, fumaroles, and steam vents that geyser skyward spectacularly, indicative of the terra infirma state of earth's surface.
Though they're not visible, the 2 tropics, Cancer and Capricorn, are nevertheless very real, the 2 parallels of terrestrial latitude lying 23 1/2deg north and south of the equator, which mark the solstitial points of the sun's greatest annual declination north and south. Similarly, the Arctic and Antarctic Circles, demarking the frigid zones of the 2 poles, are invisible but nevertheless very real. Since the latticework of longitudinal lines had to begin somewhere, Greenwich, England, is earth's great zero point, and the opposite International Date Line in mid-Pacific, where all our "artificial" days begin, is very "real" though it does not, of course, exist in fact.
Earth's elliptical journey around the sun gives us our seasons, because of the tilt of earth's axis, of 23 1/2deg, with the seasons of the northern and southern hemispheres thus alternating. Its rotation gives us night and day. Earth wobbles on its axis, because of the pull of the moon. Other motions are the precession of the equinoxes, a gradual shifting wobble that takes 25,800 years to complete, and another "nodding" motion that requires only 18.6 years.
Earth's crustal variation is very slight. The top of Mount Everest is somewhat over 5 mi. high. The bottom of the greatest deep, the Marianas Trench in the Pacific, 36,198' below sea level, is somewhat over 6 mi. down. Thus the extremes above and below sea level total a mere dozen miles! An important part of every volcano's lava is water vapor from earth's interior. Meantime, by eroding limestone, water returns below ground, at the same time creating fabulous caves with glistening stalagmites and stalactites. The Carlsbad Caverns, in New Mexico, have the largest underground "chamber," the Big Room. And Mammoth Cave, Ky., is one of the earth's longest-largest: 5 sq. mi. The bottom of the Dead Sea, 1,286' below sea level, might seem to be the lowest land "surface," but there are probably deeper "dents" below the downpressing of both the Greenland and the Antarctica glaciers.
Earth's largest saltwater lake is the Caspian "Sea," 169,350 sq. mi. Largest freshwater lake is Superior, 31,820 sq. mi. When is a lake large enough to be called a sea? When does a hill become a mountain? When is an island large enough to be called a continent? The Black Hills of the Dakotas are higher than many "mountain" ranges elsewhere in the U.S.
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