The Scriptures declare that "God ... formed the earth ... to be inhabited" (Isaiah 45:18). An impartial study of the Earth soon convinces the student that there is a tremendous amount of meaning behind this simple statement.
The Earth is the only planet circling our sun on which life as we know it could (and does) exist. A brief glance at the Earth and all other known planets finds many startling contrasts. The Earth as a planet consists mostly of iron, oxygen, sulfur, silicon, magnesium, and nickel (total, 98%), with the other two percent consisting of about a hundred other elements. Like no other planet, ours is covered with green vegetation, blue-green seas, streams, rivers, mountains, and deserts which produce a spectacular variety of color and texture—all other known planets are covered with lifeless soil which varies only according to slight movements made by wind or mild air currents. Completely barren, the surface of most planets is totally in contrast to the Earth's with its blue lakes, green oceans, huge land masses and 500,000 islands. Even from a distance, its colors are quite lively—bright greens, blues and whites—whereas the surface of all other known planets are rather dull.
Some type of life is found in every niche on the Earth. Even in the extremely cold Antarctica, hardy microscopic beings exist in ponds, tiny wingless insects live in patches of moss and lichen, and even two types of plants flower yearly. From the top of the atmosphere to the bottom of the oceans, from the coldest part of the poles to the warmest part of the equator, life persists here. To this day no sign of life has been found on any other planet.
The Earth is immense—8,000 miles in diameter and weighing roughly 6.6 x 1021 tons. If the Earth traveled much faster in its 292-million-mile-long orbit around the sun, centrifugal force would pull it away from the sun, and if too far, all life would cease to exist. If it traveled slightly slower, the Earth would move closer to the sun, and if it moved too close, all life would likewise perish. The Earth's 365 day, 5-hour, 48-minute and 45.51-second-round-trip is accurate to a thousandth of a second! If the yearly average temperature on Earth rose or fell only a few degrees, most life on it would soon roast or freeze. This change would upset the water-ice and other balances, with disastrous results. If it rotated on its axis slower, all life would die in time, either by freezing at night because of lack of heat from the sun, or by burning during the day from too much sun.
Of all the energy the sun gives off, only one billionth of its daily output is picked up by the Earth. The sun does provide the Earth with more than 130 trillion horse power each day, about fifty thousand horse power for each current resident. Even though there are likely several hundred billion galaxies in the universe, there is only one atom for every 88 gallons of space, which means most of the universe (the vast majority, actually) is empty space!
If the Moon were much nearer to Earth, one result would be huge tides which would overflow onto the lowlands and erode the mountains (and with the continents leveled, it is estimated that water would cover the entire surface to the depth of a mile and a half)! If the Earth was not tilted 23° on its axis, but was at a 90° angle in reference to the sun, we would not have four seasons. Without seasons, life would soon not be able to exist here—the poles would lie in eternal twilight, and water vapor from the oceans would be carried by the wind towards both the north and south, and would freeze when close enough to the poles. In time, huge continents of snow and ice would pile up in the polar regions, leaving most of the Earth a dry desert. Eventually the oceans would disappear and rainfall would cease. The accumulated weight of ice at the poles would cause the equator to bulge and, as a result, the rotation of the Earth would drastically change.
The Miracle of Water
Another example which illustrates the rigidity of environmental variations for life to exist is that of water. The Earth is the only planet with huge bodies of water—70% of its surface area consists of oceans, lakes, and seas surrounding huge bodies of land. The few planets that have water contain only moisture floating as vapor on their surface, not large bodies of liquid water as on Earth.
Water is unique in that it absorbs large amounts of heat without much alteration in its temperature. Its absorption speed is extremely rapid—about ten times as fast as steel. During the day, the seas rapidly soak up a great deal of heat, thus the Earth stays fairly cool. At night, the oceans release the vast amounts of heat that they soaked up during the day, which combined with atmospheric effects, keeps the surface from getting too cold at night. If it were not for the tremendous amount of water on the Earth, there would be far greater day and night temperature variations. Many parts of the surface would be hot enough to boil water in the day and the same part would be cold enough to freeze water at night. Water is an excellent temperature stabilizer. The large oceans on Earth are a vital part of our survival!
The large amount of water on the Earth could create problems, though. If something is heated, it expands, and when cooled, contracts. Thus, given two objects of the same size and material, if one is cooler, it will be heavier. This may not seem like a problem, but in the case of water, it would be, if it were not for a rare anomaly. Water, as almost all other substances, contracts when cooled, but in contrast to virtually all other materials (there are very few exceptions, such as rubber and antimony), it contracts when cooled only until it reaches 4° Centigrade then it, amazingly, expands until it freezes. If water continued to contract when cooled, it would become heavier and thus sink to the bottom of the ocean. Further, when water turned to ice, it would likewise sink to the bottom of the ocean. One result of this is that the ocean bottom would be extremely cold—and many fish would die. In time, more and more of the ocean would become ice as more froze on the surface, sank, and accumulated at the bottom.
Thus, for much of the Earth, the ice that forms in seas, oceans, and lakes stays near the surface where the sun and the warm water below melts it in the summer. Water that is warmer than 4°, being heavier, sinks to the bottom and warms the depth of the oceans. This process of surface water warming and sinking to the bottom, plus the Coriolis effect produces ocean currents. These currents, among other things, insure that most of the ocean stays in a liquid form. Indeed, "The Lord by wisdom hath founded the earth; by understanding hath He established the heavens." Proverbs 3:19.
The Miracle of Air
On the land, the opposite happens. Air, after it is warmed, rises—and the air close to the surface of the Earth is heated via light energy from the sun. The air near the surface then rises upward. The result is that the air near the Earth's surface maintains a temperature in which life can exist. If air acted the same way that water did, the temperature on the Earth's surface would be unbearable—and life could not survive for very long. The temperature a few hundred feet above the surface, on the other hand, would be quite cold and, likewise, life could also not exist there. The only habitable region would be a thin slice of air, but even here life could not exist for long. Plants and trees which would be necessary to support the life in the atmosphere could not survive as they would be in the cold zone. Thus birds would have no resting place, or food, water or oxygen. But air rises when heated and thus life can exist on the Earth.
The movement of warm air from the surface rising upward creates air currents (wind) which are an important part of the Earth's ecological system. They carry away carbon dioxide from areas which overproduce, such as cities, and move oxygen to areas in need of it, as large urban population centers.
The mixture of gases usually found in the atmosphere, without man's pollution, is perfect for life. If it were much different (more oxygen, less carbon dioxide, etc., or the atmospheric pressure was much lighter or heavier), life would cease to exist on Earth.
If our atmosphere were thinner, many of the millions of meteors which now are burned up would reach the Earth's surface, causing death, destruction and fires everywhere.
Adaptation to Environment or Creation of Environment for Life?
If evolution works to evolve life to fit the existing environments, why has it not equally conquered all of the environments here and elsewhere? Earth is far better suited for life than any other planet, yet most of the environments even here, are either too hot or too cold, too far underground or too far above ground to support much life. In the several thousands of miles of changing environments from the center of the Earth to the edge of its atmosphere, there are only a few feet of habitable environment, and therefore almost all creatures are forced to live there. Although only the Earth was made to be inhabited (Isaiah 45:18) in our solar system, even on the Earth only a thin slice is ideally suited for life.
This thin section, though, is teeming with life. It is estimated that an acre of typical farm soil, six inches deep, has several tons of living bacteria, almost a ton of fungi, two hundred pounds of one-cell protozoan animals, about one hundred pounds of yeast and the same amount of algae.
The extremely fine line between an environment where life can and cannot exist is illustrated by the fact that it is estimated that a one-degree temperature change in the average worldwide temperature would, in time, seriously affect life on the Earth, and a two-degree temperature change could be disastrous to life. The tolerances are extremely small, and if there are any other planets in the universe, it is unlikely that any of them could have life, due to the extremely rigid conditions necessary for life to exist.
The chances of a planet being just the right size, the proper distance away from the right star, etc., are extremely minute, even if many stars have planets circling them, as some speculate. The mathematical odds that all of these and other essential conditions happened by chance are astronomical—something like billions to one!
* My thanks to Dr. David Johnson, Professor of Chemistry at Spring Arbor College, and Robert Laing, President of Clean Flow Laboratories, for their help on this article.
The above article was originally published in June 1985. For an updated article, please click here.
Cite this article: Jerry Bergman, Ph.D. 1985. The Earth: Unique in All the Universe. Acts & Facts. 14 (6).
Habitable alien planets similar to Earth may not be that rare in the universe, a new study suggests.
About one in five sunlike stars observed by NASA's planet-hunting Kepler spacecraft has an Earth-size planet in the so-called habitable zone, where liquid water — and, potentially life — could exist, according to the new study. If these results apply elsewhere in the galaxy, the nearest such planet could be just 12 light-years away.
"Human beings have been looking at the stars for thousands of years," said study researcher Erik Petigura, a graduate student at the University of California, Berkeley (UC Berkeley). "How many of those stars have planets that are in some way like Earth? We're very excited today to start to answer that question," Petigura told SPACE.com. [9 Exoplanets That Could Host Alien Life]
The findings, detailed today (Nov. 4) in the journal Proceedings of the National Academy of Sciences and in a video describing the frequency of Earth-like planets, say nothing about whether these planets actually support life — only that they meet some of the known criteria for habitability. Petigura also presented the results today in a briefing at the second Kepler Science Conference at NASA Research Park in Moffett Field, Calif, in which the Kepler team also announced the discovery of hundreds of new exoplanets, including many in the habitable zone.
"I think it's by far the most trustable estimate available, but I don't think it's final," said Francois Fressin, an astronomer at the Harvard-Smithsonian Center for Astrophysics who was not involved with the study.
To find these Earth-size exoplanets, Petigura and his colleagues used Kepler's measurements of stellar brightness to look for signs of dimming, known as transits, as planets crossed in front of their host star.
Taking a planet census
Petigura and his colleagues painstakingly developed software to sift through Kepler's mammoth data set. The spacecraft's field of view includes about 150,000 stars, but most of these fluctuate in brightness too much for a planet to be detectable. The team examined 42,000 of the "quietest" stars, finding 603 planet candidates around these stars, 10 of which were Earth-size and lay in the habitable zone.
The team defined Earth-size planets as ones having a radius one to two times that of Earth. Planets were considered to be in the habitable zone if they received about as much light as the Earth does from the sun (within a factor of four). [7 Ways to Discover Alien Planets]
They used the Keck I telescope in Hawaii to take spectra of the stars, in order to pin down the radii of the planets.
But this wasn't the end of the story. Just as taking a census requires some statistical corrections for the people the survey misses, the researchers had to make corrections for planets Kepler missed.
The transit method of finding planets, by definition, only detects planets orbiting in the same plane of view as their host star, which includes just a fraction of the total number of planets. Study researcher Geoff Marcy of UC Berkeley compared planetary orbits to papers fluttering through the air. Very few are going to be edge-on, he said.
Secondly, the analysis misses some planets simply because the tiny amount of starlight they block makes them tricky to detect. To correct for this, the researchers inserted "fake planets" into the data so they could see how many their software would miss.
The analysis was a "Herculean task," Marcy said.
After making these corrections, the researchers had their result: About 22 percent of sunlike stars observed by Kepler have Earth-size, potentially habitable planets.
Chances for life
The researchers were quick to point out that the fact that these planets are Earth-size and lie in the habitable zone does not mean they could support life. The planets might have scorching-hot atmospheres, or no atmospheres at all, they said. Even if the planets have all the basic ingredients for life, scientists don't know the probability that life would ever get started.
The definition of Earth-size planets in this study was pretty broad, Fressin said. For instance, a planet that has a radius twice the size of Earth's might not even be rocky, he said.
Kepler mission scientist Natalie Batalha, an astronomer at NASA's Ames Research Center who was not involved with the study, agrees it's a generous definition. Rocky planets with a radius about 1 to 1.5 times the size of Earth's have been found, but the fraction of larger planets that are rocky is probably much lower, Batalha told SPACE.com. Still, it's a fair start, she said.
"Kepler's prime objective was to understand the prevalence of habitable planets in the galaxy," Batalha said at a news conference. "This is the first time a team has offered such a number for stars like the sun."
The researchers had to extrapolate the number of planets with orbits longer than 200 days, because these haven't been detected in the Kepler data. "Ideally, we won't rely on extrapolations," Batalha said. "But as a first cut, this is a valid thing to do."
Last week, Marcy and his colleagues reported the discovery of the alien planet Kepler-78b, a rocky world nearly the same size and density as the Earth. But Kepler-78b hugs its star at a distance far too close and hot to be habitable, with surface temperatures of about 3,680 degrees Fahrenheit (2,027 degrees Celsius).
Kepler went out of commission in May, after the loss of a wheel used for pointing the spacecraft. Nevertheless, scientists will mine Kepler data for decades to look for potentially habitable planets.
"Maybe with future instruments, we could actually image these planets," Petigura said.
Follow Tanya Lewis on Twitter and Google+. Follow us @Spacedotcom, Facebook and Google+. Original article on SPACE.com.
Astronomers have confirmed more than 800 planets beyond our own solar system, and the discoveries keep rolling in. How much do you know about these exotic worlds?
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Alien Planet Quiz: Are You an Exoplanet Expert?
Astronomers have confirmed more than 800 planets beyond our own solar system, and the discoveries keep rolling in. How much do you know about these exotic worlds?
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