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Spaceship Earth: A Rare Jewel

Earth
“Are we alone in the universe?”  This question has stirred the imaginations of people for as long as anyone can remember.   Is there an “ET” out there somewhere trying to contact us?  Discovery of alien life is the prime theme for science fiction movies and TV shows.  Given the vastness of the universe, with countless galaxies and star systems, it seems logical that there must be millions of inhabitable earth-like planets (“class M” planets for you Trekkies).  This idea has likely been fueled by recent discoveries of a number of extra-solar planets (that is, planets outside our own solar system).  As of July 2016, the discovery of 2933 confirmed “exoplanets” has been reported, with many other potential ones being investigated.  Nearly 300 exoplanets are considered to be in the “habitable zone” or “Goldilocks zone,” that is the temperature range that would be favorable for liquid water.  (This doesn’t take into account other factors such as deadly x-ray or ultraviolet emissions from the host star.)[1]

Indeed, one of the stated missions of NASA is “To explore the universe and search for life.”[2]  Some think that life must have originated in outer space somewhere, given the tremendous odds against life forming by itself from non-living matter here on earth.

In their 2004 book The Privileged Planet Drs. Jay Richardson and Guillermo Gonzales explore the amazing uniqueness of Earth and the improbability of another earth-like planet anywhere in the universe.  That earth is such a special place only becomes apparent after we consider all the conditions necessary to support life, and compare them with the array of conditions existing in the rest of the galaxy.

Mars

Just what makes earth so special?  Consider, for instance, that the planet must be just the right size to sustain life.  If it were much smaller, gravity would be weaker, and earth wouldn’t be able to hold as much atmosphere.  The air would be thinner, and it would be more difficult to get the oxygen we need.  The most earth-like planet in the solar system, Mars, has a gravitational field 38% as strong as ours, and its atmosphere is so much thinner than ours that the average surface temperature is a frigid -81°F.  In spite of recent claims that micro-organisms once inhabited the planet, no life has been discovered there.

If earth were too large, the force of gravity could be crushing, and if the atmosphere were too thick beyond a certain point, life would be inhibited.  A planet twice the size of earth would have about 3½ times the gravitational attraction.

Our sun is rather unique as a star.  The vast majority of stars are smaller and cooler.  Ours is just the right size to produce radiant heat and light to sustain life.  Most stars produce lethal radiation such as gamma and x-rays in much greater proportion than visible light.  The emission of the sun peaks at the energy level ideal to promote growth of plant life on earth.

 

Sun
Our sun’s output of energy is very steady and reliable compared to other stars.  Most stars vary considerably in intensity, ranging from 10% of normal to 150,000% (in the case of pulsars and neutron stars) over time.  If the sun’s output varied by just 10%, life wouldn’t be possible on earth.

To support life, a planet must be free from harmful radiation.  Although most of the sun’s output is beneficial, it also emits high-energy particles, mostly electrons, protons, and alpha particles.  Earth’s magnetic field protects us from the deadly effects of these particles.  Not all planets have magnetic fields.

Earth’s orbit is ideal for supporting life.  It’s nearly circular and just the right distance from the sun to give us a temperature range to make life possible.  A smaller or larger orbit could cause us to roast or freeze.  Most of the other seven planets (eight if we count the recently demoted dwarf planet Pluto) have somewhat elliptical orbits.  If earth’s orbit were elliptical, there’d be large temperature swings from one side of our orbit to the other.

 

There are many other factors that make earth unique: location in the galaxy, our moon, the tilt of the axis, the speed of rotation about the axis, the composition of the atmosphere, and so on.  But let me dwell on just one factor that makes earth unique among planets.  Earth is known as “the water planet” because about ¾ of the surface of our planet is covered with water.  Without the oceans we’d live on a desert planet like Mars, and once again life wouldn’t be possible.  No other planet that we know of has a surface mostly covered by water. 

 

These are only a few of the dozens of characteristics that have to be just right in order for life to exist on our home planet.  The authors of The Privileged Planet estimate the odds of a planet forming with so much water to be about one in 10 to the 158th power.[3]  This is beyond the possibility of an earth-like planet forming by chance, as statisticians generally agree that when the odds of an event occurring are one in 10 to the 50th power or less, it’s impossible.

 

Given these odds it would seem that planet Earth is very unique.  The chances that there is another Earth-like planet are infinitesimally small.

Carl Sagan in his book Pale Blue Dot seems to agree: “Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity, in all this vastness, there is no hint that help will come from elsewhere to save us from ourselves.”

Like Sagan, I’m not holding my breath for aliens from another galaxy to save us.  On the other hand, I don’t share his pessimism.  Because, after all, we’re not really alone.  In fact, God sent his Son to save us from ourselves.  We can have a bright future if we accept the free gift that He’s provided for us. 


[1] exoplanets.org; also nasa.gov/kepler; J. of Creation 29(2) 2015 “Exoplanets—Habitable or Not?”

[2] Although this quote is no longer on the NASA website, many articles express the same thought.  See for example, www.nasa.gov/vision/universe/starsgalaxies/search_life_I.html.

[3] Richardson, Jay and Gonzales, Guillermo, The Privileged Planet, p. 327

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