Was the Earth Fine-Tuned for Life?
The argument for Intelligent Design is based on the idea that the conditions necessary for life are too perfect, and the complexity of DNA is so great that there must be an intelligence behind the creation of all life and intelligence.
Lets look at the earth and the variables involved that must be “just right” for life to exist, apart from the argument of how life began. I will offer some of the variables and the estimated probability that any planet would have that condition so that we can calculate the probability of ANY planet being so suited for life after we see the most important factors involved. These factors were chose for a specific property and reason. Change any factor listed below significantly and life on earth could not exist.
SIZE AND GRAVITY: There is a range for the size of a planet and it gravity which supports life and it is small. A planet the size of Jupiter would have gravity that would crush any life form, and any high order carbon molecules, out of existence. Of the 8 planets + Pluto in our solar system there are 3 that fall within that range, Venus, Earth, and Mars. There is the possibility of some of the moons of Saturn and Jupiter being within the range but nothing conclusive. An estimated guess of probability - .4 or 4 out of 10
WATER: Without a sufficient amount of water, life could not exist. For reasons that go back to the early beginning of the solar system, the earth is the only planet known with ANY significant amount of water. Of the planets of our solar system only earth meets that requirement. Estimated probability - .1
ATMOSPHERE: Not only must a planet have an atmosphere, it must have a certain percentage of certain gasses to permit life. On earth the air we breath is 78% nitrogen, 21% oxygen, and 1% argon and carbon dioxide. Without the 78% nitrogen to “blanket’ the combustion of oxygen, our world would ‘burn up’ from oxidation. Nitrogen inhibits combustion and permits life to flourish. No other planet comes close to this makeup of atmosphere. Estimated probability - .01
OXYGEN: The range of oxygen level in the atmosphere that permits life can be fairly broad, but oxygen is definitely necessary for life. Mars falls far short in that respect, and so does Venus. The amount of ‘pure’ oxygen in the atmosphere is dependent on many things, like volcanism, thermal activity in the core of the planet, and the amount of metal in the crust. Too much metal would absorb the oxygen in the air in the form of rust and oxidation. Estimated probability - .01
RARE EARTHS MINERALS: Many chemical processes necessary for life are dependent on elements we call ‘rare earth’ minerals. These only exist as ‘trace’ amounts, but without which life could not continue. Estimated probability - .1
THE SUN: Our sun is an average star in both composition and size. The larger a star is the faster it burns out. It would take longer for life to develop than those larger stars would exist. Smaller stars last longer but do not develop properly to give off the heat and radiation necessary to sustain life on any planets that form. The smaller the star the less likely it will form a planetary system at all. Estimated probability - .3
DISTANCE FROM THE SUN: To have a planet with a surface temperature within the bounds for life, it must be within the ‘biosphere’ of a star, a temperate zone of a given distance from the source of radiation and heat. That would depend on the size of the star. For an average star the size of our sun, that distance would be about 60 to 150 million miles. Estimated probability - .2
RADIOACTIVITY: Without radioactivity, the earth would have cooled to a cold rock 3 billion years ago. Radioactivity is responsible for the volcanism, and heat generated in the interior of the earth. Volcanism is responsible for many of the rare elements we need as well as the oxygen in the air. Most rocky planets have some radioactivity. Estimated probability .5
DISTANCE AND PLACEMENT FROM THE GALACTIC CENTER: We receive very little of the x-rays and gamma rays given off from the galactic center, that would affect all life and its development on earth. We live on the outer rim of the Milky Way, in a less dense portion of the galaxy, away from the noise, dust, and dangers of the interior. Estimated probability - .5
THE OZONE LAYER: Animal life on land survives because of the ozone layer which shields the ultraviolet rays from reaching the earth’s surface. The ozone layer would never have formed without oxygen reaching a given level of density in the atmosphere. A planet with less oxygen would not have an ozone layer. Earth is the only planet in the solar system with an ozone layer. Estimated probability - .1
VOLCANIC ACTIVITY: Volcanic activity is responsible for bringing heaver elements and gasses to the surface, as well as oxygen. Without this activity, the planet would never have sustained life in the first place. Mars once had such activity, but appears to be inactive now. Estimated probability - .3
EARTH’S MAGNETIC FIELD: We are bombarded daily with deadly rays from the sun, but are protected by the earth’s magnetic field. Mars does not have a field and thus, most of its atmosphere and water were ‘blown away’ early in its life by the solar wind. Estimated probability - .2
SEASONS: Because of the earths tilt, we have seasons, and no part of the earth is extremely hot or cold. The seasons have balancing effect of the temperature on the surface and cause the winds and sea currents which we and all life depend on for a temperate climate. Mars has seasons but little atmosphere. Other planets have extreme tilts. Estimated probability - .2
THE MOON: Most people don’t think of the moon as necessary for life. We have the tides that are very important for some species, but the very early collision of a smaller Mars sized planet and the earth is what caused the moon. It also tilted the earth on its axis and caused seasons. The earth and moon should more accurately be called a ‘two-planet’ system, as the size of earth’s moon is greatly larger in proportion to the earth, than any other planet. The moon early in its existence also shielded the earth from bombardment by meteor showers that were devastating. The craters on the moon are the evidence of that factor. No other planet has undergone such a unique event in its history. Estimated probability - .0001
If any one of the above factors were missing, life could not have survived or developed on planet earth.
Multiplying all the probabilities of the above will give us the probability of any given planet having the conditions necessary for life.
Or seven chances in 10 quadrillion possibility. (for those following the U.S. budget, one quadrillion is a thousand Trillion)
It is evident from the math that the earth is a very special place in the universe. To say it is the only place like it would be speculative and unreasonable, given the immeasurable number of planets that must exist around the trillions of stars in other galaxies as well as our own. However we can’t say for sure, because we have yet to discover another planet like it among the “exoplanets” so far discovered. One reason is our limited ability to analyze any planet smaller than “Jupiter-size” at the distances we are searching.
For all practical purposes the earth is very unique and is truly a “garden” amidst the desert of rocky barren planets we know of. The more we learn of the universe, the more the earth appears to be the extreme exception to the norm.
Was it “fine-tuned”? From the evidence, what do you think?