The Case for a Creator, Chapter 7
Most of chapter 7 focuses on Guillermo Gonzalez’s “privileged planet” hypothesis. This argument, as he uses it here, consists of listing every way in which our planet or our solar system could have been different, and concluding that every single one of them would be completely fatal to life.
Throughout this chapter, neither Strobel nor Gonzalez ask any of the obvious follow-up questions, such as whether different kinds of life could exist in these conditions, whether life like Earth’s could have adapted, or even whether there are living things on Earth that already deal with very similar challenges (as we’ll see, in many cases, there are). Instead, their reigning assumption is that life as a whole is as fragile as a soap bubble, and even a single change to Earth’s parameters would have been catastrophic for the entire biosphere.
There are more arguments tossed out in this chapter than I could do justice to in a single post, so I’m splitting my responses up into several parts. This is the first post of what will either be two or three.
According to Gonzalez, the presence of Jupiter in our solar system “acts as a shield to protect us from too many comet impacts” [p.173]. Jupiter’s enormous mass and gravitational pull “deflects comets and keeps many of them from coming into the inner solar system, where they could collide with Earth with life-extinguishing consequences… If you want to get an idea of the stuff that probably would have hit the Earth [without Jupiter], look at the surface of the moon.” [p.174]
I’m not sure what point Gonzalez thinks he’s making here. Is he saying that Jupiter’s gravitational pull somehow shields the Earth but not the Moon? The two are so close, in astronomical terms, that any reputable scientist would find this laughable. Rather, the Moon’s surface preserves evidence of the kind of bombardment that both the Earth and the Moon were subjected to early in the history of the solar system, Jupiter’s presence notwithstanding. The Moon, which has no erosion, still bears these scars, while the Earth has largely erased them.
Although there’s no denying that Jupiter’s gravitational shield has deflected many cosmic objects that could otherwise have made it into the inner solar system, I’m far from convinced that this is an absolute necessity. As just mentioned, Earth did suffer a heavy bombardment early in its history, but that did not prevent life from forming here (soon after the bombardment had ended, in fact). Today, most of the lingering planetesimals and other stray rocks left over from the solar system’s formation have been cleaned out, and large impacts on our planet are relatively infrequent, Jupiter or no. And even when Earth has been hit by large objects, although mass extinctions ensued, life as a whole did not die out.
Next on Gonzalez’s list is the low eccentricity of the Earth’s orbit – i.e., the shape of our orbit is nearly circular. This keeps us in what he calls the “circumstellar habitable zone”, the Goldilocks region where liquid water can exist and the planet neither overheats, like Venus, nor freezes, like Mars.
“So if the Earth’s distance from the sun were moved by, say, five percent either way, what would happen?” I asked.
“Disaster,” came his quick reply. “Animal life would be impossible.” [p.174]
It’s not hard to believe that a change in atmospheric composition could keep our planet livable even if we were closer to, or farther from, the Sun. In fact, the Sun’s output of energy is not a constant, but has changed dramatically – not by a mere 5%, but by as much as 30% – over the lifetime of our solar system. Yet the Earth’s geologic records show that it’s had a warm surface and liquid water throughout that time. This is the so-called faint young sun paradox, and the favored scientific explanation does invoke changes in atmospheric greenhouse gas concentrations.
And even if the Earth’s temperature did vary due to a more elliptical orbit, there’s no reason to believe that would have been disastrous for life. Richards claims, “It doesn’t do you any good to have melted water for four months and then have the whole planet freeze up again” [p.174]. I’m sure that would come as a surprise to the arctic species that already cope with very similar conditions: a brief, warm growing season followed by months of dark and cold. In fact, some geologists believe that around 700 million years ago, nearly the entire planet was covered with ice, and that did not extinguish life either.
ID advocates are particularly enamored of the Moon, especially since we’ve learned that it formed from a gigantic impact early in the solar system’s history – the kind of unlikely event that they love to use as evidence of divine providence. Quoth Gonzalez:
“There was a remarkable finding that the moon actually stabilizes the tilt of the Earth’s axis… The tilt is responsible for our seasons.” [p.179]
He does not explain why the existence of seasons is a prerequisite for life; nor does he address the obvious point that equatorial and arctic regions, which experience little seasonal variation, support plenty of life.
Gonzalez goes on to say that if the Moon were not there, Earth’s axial tilt could vary wildly, and if it were much more massive, it could slow down the Earth’s rotation far more than it does. Either way, he worries, “you could have large temperature differences between day and night.” [p.180]
Again, there are already species on Earth that cope with large temperature swings between day and night. The Sahara Desert, for example, sees diurnal variations of almost 100°F, but is not lifeless – the major limiting factor for life is the availability of water, not the temperature.
It’s probably true that living on Earth would be more difficult if there were more frequent asteroid impacts, or more drastic temperature swings, or more chaotic seasonal variation. But this is a far cry from saying that life on Earth would be impossible. Based on the climactic extremes that other living species and even other human societies already deal with, we have every reason to believe that life would continue to thrive, even in the presence of the parade of horribles that Gonzalez invokes.
Other posts in this series: