The Privileged Planet

In my recent blog posting, The Razor's Edge, I wrote about the fine-tuning of the universe. Now let's travel a little closer to home. For years astronomers thought the Earth was a rather ordinary planet - nothing exceptional. As Carl Sagan wrote in 1994, the earth is "a lonely speck in the great enveloping comic dark". However the modern day astronomical thinking has been turning in a different direction. Dr Peter Ward and Dr. Donald Brownlee wrote a book, The Rare Earth, which makes a case that the conditions for life on Earth are very rare indeed. As they say, it is "inescapable" that "Earth is a rare place indeed. Astronomer David Levy agrees by writing "As we know it on Earth, complex life might be very rare, and very precious. Astronomers Jay Wesley Richards and Guillermo Gonzalez recently authored a book called The Privilege Plant also records astounding evidence which shows how many things had to go right to support life on Earth. Here are some of those conditions.

Earth is located in the Milky Way galaxy which is suited to supporting life. You can't find life in old globular clusters due to 1) lack of heavy atoms needed for life, and 2) unstable orbits due to the density of stars.

The Earth is in what is know as the "inhabitable zone" within the Milky Way which about half-way out in the spiral arm. Near the center of the galaxy there are too many exploding stars and black holes to be safe. This would not only be dangerous in itself but the increased amount of radiation which is not hospitable for life. If positioned farther out on the arm there would be insufficient heavy elements for life.

If we look at our solar system we see the earth with a nearly circular obit. If earth had a highly elliptical orbit, the temperature extremes on earth would be too extreme for life. Also, if the massive planets such as Jupiter had eccentric orbits, this would disrupt the earth's steady orbit.

The larger, more massive planets such as Jupiter shield our planets from comet impacts. This was shown in 1994 by George Wetherill of the Carnegie Institution.

The earth is just the right distance from the sun to sustain life. 5 per cent closer or father and life would be be possible.

Our sun is quite unusual. It is just the right size and type. About 80% of the stars are red giants which would not be suitable to support a life-sustaining planet. This is due to many factors including 1) the planet must be close to a red dwarf to get enough heat but that that exposes to the planet to solar flares and also cause the planet to be in rotational "lock" 2) the sun's output is very stable which is essential for life, not so for many other stars, 3) our sun has the perfect balance of red and blue hues for heat and for photosynthesis.

Our extremely large moon stabilizes the earth's axis. This was only discovered in 1993. Also, the tide cause by the large moon are very benefical since it nourishes the ocean and keeps the ocean currents going. If the moon were more massive it slow down the earth.

The earth's mass produces a optimum gravitational field; large enough to hold the atmosphere but not too large like Jupiter.

The Earth has the optimum carbon dioxide - rock cycle to regulate the greenhouse gases.

The Earth's molten core produces a magnetic field which shields the Earth from dangerous radiation.

There are many more elements of earth's design for life. For futher reading, refer to these two books.

The Rare Earth

The Privaleged Planet

As a postscript, Dr. Guillermo Gonzalez was denied tenure due to the his science leading him to conclude the earth was designed for life.

For more on this postscript, read this.