"Enjoy the Journey" Proverbs 3: 5,6

Apologetics Series #5: Earth…the Privileged Planet

“As we survey all the evidence, the thought insistently arises that some supernatural agency–or rather, Agency– must be involved. Is it possible that suddenly, without intending to, we have stumbled upon scientific proof of the existence of a Supreme Being? Was it God who stepped in and so providentially crafted the cosmos for our benefit?” (Greenstein 27).

The suggestion that God created the entire universe and all the creatures in it “is very from a discredited prescientific myth. In fact, no observation has ever laid the presumption to rest. And today, four centuries after the scientific revolution, the doctrine is again re-emerging. In these last decades of the twentieth century, its credibility is being enhanced by discoveries in several branches of fundamental science” (Denton 3-4).

Everything about our existence is amazing! God has placed us so perfectly within the galaxy, within the universe even, that life is perfectly possible here on Earth. Let’s take a look at some of those incredible circumstances that bolster the case for our uniqueness in the universe and the likelihood of a personal and omnipotent Creator.

Our Location within the Galaxy

Within our galaxy, the Milky Way, there is a small zone in which a habitable planet can lie. This is known as the Galactic Habitable Zone, in which Earth lies. In all other parts, there are too many threats to life, making it impossible for them to exist and be habitable.

Our galaxy is a spiral galaxy, which means that it is comprised of a “center spherical bulge and a disk with ‘spiral arms’ extending outward from the nucleus in a spiral pattern, resembling a celestial pinwheel” (177). The composition of this galaxy changes as you go outwards from the center; There are more heavy elements towards the center, and significantly less in the spiral arms. Therefore, the outer regions are a lot less likely to have Earth-type planets.

Moreover, the rate of active star formation is more prevalent in the outer spiral arms and in the inner regions, which is extremely hazardous. Where there is active star formation, there is also supernovae exploding at rapid rates, threatening all matter nearby.

Additionally, the inner region is extremely dangerous due to the massive amounts of gamma, x-ray, and particle radiation emitted from a black hole when it sucks in nearby matter. Therefore, this black hole in the nucleus of the galaxy provides a two-fold problem. On one hand, no massive particles can get anywhere near it or it will be sucked up and never seen again; On the other hand, when this occurs, the massive release of energy threatens all other matter in the area.

So we can’t go too close to the inner regions or to the outer spiral arms. Luckily, we were placed safely between the Sagittarius and Perseus spiral arms, and far enough away from the black hole at the inner region. It is pretty well-established that there could be no other life within our galaxy.

Our Location within the Universe

There are three types of galaxies in the universe: spiral, elliptical, and irregular. The first, again, is pinwheel-shaped, an elliptical galaxy is egg-shaped and the stars within it all have very random orbits, and lastly is the irregular galaxy which has no organization. Could we have survived in any of the other galaxies?

Most galaxies are elliptical, so let’s start there. Elliptical galaxies cannot support life because all of the stars within visit every region of the galaxy. Therefore, they are bound to pass through the dangerous dense inner regions, risking both supernovae and a possible black hole. (The Hubble telescope has found that nearly every large nearby galaxy has a giant black hole at the nucleus). Moreover, because they lack the heavy elements necessary to form them, an Earth-like planet cannot exist in this type of galaxy.

Irregular galaxies are worse, because they are “distorted and ripped apart, with supernovae going off throughout their volume. There are no safe places” (180). If you take just the spiral arms of a spiral galaxy and make a separate galaxy out of it, then you’d basically have an irregular galaxy. There is absolutely no chance for life with that sort of supernovae activity.

Other spiral galaxies will have the same very narrow habitable zone as the Milky Way does. However, our galaxy is in the top 1-2% of the most massive and luminous. The smaller the galaxy, the fewer heavy elements it will have and the smaller the chance that an Earth-like planet can form. In conclusion, there is an extremely small chance that a planet like ours could exist anywhere else, with the elements necessary for life.

“In terms of habitability, […] we are in the best possible place […] because our location provides enough building blocks to yield an Earth, while providing a low level of threats to life. […Nowhere else is] as friendly to life as our location. Sometimes people claim you can be in any part of any galaxy. Well, [astronomer and physicist Guillermo Gonzalez has] studied other regions–spiral arms, galactic centers, globular clusters, edges of disks– and no matter where it is, it’s worse for life. I can’t think of a better place than where we are” (181). The surmounting evidence lead Gonzalez to declare that Earth is a “privileged planet.”

Our Nearly Perfect Circular Orbit

Another unique aspect of our planet and those within our solar system, is the near perfect circular nature of our orbits. If we had a slightly more elliptical orbit, then we would be sensitive to the gravity of the nearby planets. They would knock our orbit off track and cause such variations within the surface temperature as would be dangerous to life. Moreover, if a large planet like Jupiter had a more elliptical orbit, then this same problem would occur whenever it came close. Our temperature and climate would be wildly unpredictable and unable to support life.

Out of all of the planets that have been discovered orbiting other G-2 stars since 1995, our solar system is the only one that illustrates the near-perfectness of the circular orbits which allows the life-supporting stability that we have.

The Perfect Distance from the Sun

The Circumstellar Habitable Zone refers to the region around a star in which a planet can have enough liquid water on the surface to host life, and is determined by the amount of light received from the host star (in this case, the sun). If we are too close, then the oceans begin to boil and the water evaporates. If we are too far, then the water gets too cold and freezes. In both of these situations, life is impossible. Moreover, that is why a circular orbit is necessary to keep us within this zone continuously.

There will be a part two to this blog to follow next week! Thanks again for reading! I hope you enjoy. As always, feel free to leave a question or comment.

-Allison Shockley

For more information…

Denton, M. Nature’s Destiny. New York: The Free Press, 1998.

Gonzalez, G., & Richards, J.W. The Privileged Planet. Washington, D.C.: Regenery, 2004.

Greenstein, G. The Symbiotic Universe. New York: William Morrow, 1988.

Jastrow, R. God and the Astronomers. New York: W.W. Norton, 1992.

Sampson, P. Six Modern Myths. Downers Grove, Ill: InterVarsity, 2000.

Strobel, L. A Case for a Creator. Grand Rapids, MI: Zondervan, 2004.

Ward, P., & Brownlee, D. Rare Earth. New York: Copernicus, 2000.


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