A Planet Perfect for Life
Could life on earth be the product of a blind watchmaker or no watchmaker at all? Could it be strictly the result of blind chance?
Some scientists have concluded that earth may be the only planet in the universe that harbors life because the conditions necessary for life are so exacting that the possibility of life on other planets is infinitesimal.
Earth's atmosphere is one way our planet is finely tuned for life. No other planet in our solar system has anything remotely like it. High in the atmosphere, ozone blocks cancer-causing radiation emanating from the sun. The atmosphere shields us from meteors, burning up the overwhelming majority long before they reach earth. Otherwise they would cause great damage and loss of life.
Our atmosphere contains a mixture of gases in perfect proportions to sustain life. Oxygen makes up 21 percent of our air. Without oxygen, all animate life—including humans-would die in minutes. But too much oxygen is toxic and makes combustible materials more flammable. If the proportion of oxygen in the air increased to only 24 percent, destructive fires would frequently break out and be much harder to bring under control. Objects around us could literally burst into flame.
Nitrogen, making up 78 percent of earth's atmosphere, dilutes the oxygen and serves a vital function as a fertilizer for plants. During thunderstorms millions of lightning bolts around the earth each day combine some nitrogen with oxygen, creating compounds that are then washed to earth by rain, where they can be utilized by plants.
Carbon dioxide makes up much of the rest of our atmosphere. Without it plant life would be impossible. Plants require carbon dioxide, which they take in while giving off oxygen. Animals and humans are the opposite, breathing in oxygen and exhaling carbon dioxide. Plant life sustains human and animal life and vice versa in a magnificent, precise, self-sustaining cycle.
Even the thickness of the earth's crust plays a part in regulating our atmosphere. If earth's crust were much thicker, it would hoard oxygen below the surface as oxides. But a thinner crust would leave us susceptible to frequent earthquakes and devastating volcanoes that would permeate our atmosphere with volcanic ash.
How important is the precise balance in our atmosphere? Our neighboring planet Venus suffers from what is thought to be a runaway greenhouse effect in which heat is trapped and cannot escape. One NASA astronomer noted that our sterile, lifeless moon "is a friendly place compared to Venus, where, from skies forty kilometers high a rain of concentrated sulfuric acid falls toward a surface that is as hot as boiling lead" (Robert Jastrow, God and the Astronomers, 1992, p. 117).
Earth's size and position
Another condition that makes the earth hospitable for life is its size, which determines its gravity and in turn affects its atmosphere. If earth were only a little larger, making its gravity slightly stronger, hydrogen, a light gas, would be unable to escape earth's gravity and would collect in our atmosphere, making it inhospitable to life. Yet, if earth were only slightly smaller, oxygen—necessary for life—would escape, and water would evaporate. Thus, if earth were slightly larger or smaller, human life could not have existed on earth.
The earth travels through space at 66,600 miles an hour as it orbits the sun. That speed perfectly offsets the sun's gravitational pull and keeps earth's orbit the proper distance from the sun. If earth's speed were less, it would be gradually pulled toward the sun, eventually scorching and extinguishing life. Mercury, the planet closest to the sun, has a daytime temperature of about 600 degrees Fahrenheit.
On the other hand, if earth's speed were greater, it would in time move farther away from the sun to become a frozen wasteland like Pluto, with a temperature of about minus- 300 degrees, also eliminating all life.
As earth rotates in its orbit, it is tilted at a 23.5-degree angle relative to the sun. Although not a direct factor in whether life is possible, the angle creates the change of seasons we are able to enjoy. Were the earth not tilted, our climate would always be the same, with no change of seasons. If the tilt were greater, summers would be considerably hotter and winters much colder, wreaking havoc on plant cycles and agriculture.
So many of earth's forms of life are dependent on an environment in which liquid water is stable. This means that earth must not be too close or too far from the sun. Astronomers estimate that, if the distance from earth to the sun changed by as little as 2 percent, all life would be extinguished as water either froze or evaporated.
Another factor making life on earth possible is frozen water's set of unusual characteristics. Ice is such a common substance that most of us do not stop to consider that the balance of life depends on the simple chemical properties of ice.
Ice is one of the few substances that expands when frozen. Most substances when frozen become more dense and sink when placed in a container of the same substance in liquid form. But not ice. Since water expands by one tenth its volume when frozen, frozen water has the unusual characteristic of floating on top of liquid water. When rivers and lakes freeze in the winter, they freeze from the top down. If ice acted like almost all other compounds, it would sink, and rivers and lakes would freeze from the bottom up. All bodies of water would eventually become solid bodies of ice, eliminating most life as we know it.
Astronomer Hugh Ross points out some of the other ways earth is perfectly balanced for life to exist: "As biochemists now concede, for life molecules to operate so that organisms can live requires an environment where liquid water is stable. This means that a planet cannot be too close to its star or too far away. In the case of planet Earth, a change in the distance from the sun as small as 2 percent would rid the planet of all life . . .
"The rotation period of a life-supporting planet cannot be changed by more than a few percent. If the planet takes too long to rotate, temperature differences between day and night will be too great. On the other hand, if the planet rotates too rapidly, wind velocities will rise to catastrophic levels. A quiet day on Jupiter (rotation period of ten hours), for example, generates thousand mph winds . . ." (The Creator and the Cosmos, 1993, pp. 135-136).
In contrast to Jupiter's 10-hour rotation, our neighboring planet Venus rotates once every 243 days. If earth's rotation took as long, plant life would be impossible because of the extended darkness and extremes of heat and cold from such long days and nights.
Our amazing solar system
Dr. Ross describes how other planets in our solar system play a vital role in preserving life on earth: "Late in 1993, planetary scientists George Wetherell, of the Carnegie Institution of Washington, D.C., made an exciting discovery about our solar system. In observing computer simulations of our solar system, he found that without a Jupiter-sized planet positioned just where it is, Earth would be struck about a thousand times more frequently than it is already by comets and comet debris. In other words, without Jupiter, impacts such as the one that wiped out the dinosaurs would be common.
"Here is how the protection system works. Jupiter is two and a half times more massive than all the other planets combined. Because of its huge mass, thus huge gravity, and its location between the earth and the cloud of comets surrounding the solar system, Jupiter either draws comets (by gravity) to collide with itself, as it did in July 1994, or, more commonly, it deflects comets (again by gravity) right out of the solar system. In Wetherell's words, if it were not for Jupiter, 'we wouldn't be around to study the origin of the solar system.'
"Neither would we be around if it were not for the very high regularity in the orbits of both Jupiter and Saturn. Also in July 1994, French astrophysicist Jacques Laskar determined that if the outer planets were less [orbitally] regular, then the inner planets' motions would be chaotic, and Earth would suffer orbital changes so extreme as to disrupt its climatic stability. In other words, Earth's climate would be unsuitable for life . . . Thus even the characteristics of Jupiter and Saturn's orbits must fit within certain narrowly defined ranges for life on Earth to be possible . . .
"The moon plays a critical role for life as well. Our moon is unique among solar system bodies in that it is so large relative to its planet. As a result, our moon exerts a significant gravitational pull on Earth. Thanks to this pull, coastal sea waters are cleansed and their nutrients replenished, also the obliquity (tilt of the rotation axis relative to the orbital plane) of Earth is stabilized (a critical factor for avoiding climatic extremes) . . . So we see that Earth is prepared for life through a variety of finely tuned characteristics of our galaxy, star, planet, and moon.
"This discussion by no means exhausts the list of characteristics that must be fine tuned for life to exist. The astronomical literature now includes discussions on more than forty different characteristics that must take on narrowly defined values. And this list grows longer with every new year of research" (ibid., pp. 137-138).
No wonder the Genesis creation account concludes with this summary of God's handiwork: "Then God saw everything that He had made, and indeed it was very good" (Genesis 1:31).
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