Recent studies conducted on Venus and Mars illustrate just how carefully fine-tuned a planet’s abundance of sulfur must be for life to be possible.
Sulfur plays a crucial role in life chemistry. This fact became personal for me a year ago when I was diagnosed as sulfur deficient. Many protein functions crucially depend on sulfur. Fortunately, most agricultural soils contain plenty of sulfur that vegetables, like onions and garlic, readily absorb. So, now that my sulfur deficiency has been resolved, my family has requested that I back off on the garlic.
Too much sulfur, however, can lead to consequences far more devastating than bad breath. Acid rain results from industrial activity pumping too much sulfur compounds into the atmosphere. Many life-essential metabolic reactions are adversely affected by the acidic conditions brought about by sulfur pollution.
One reason life thrives on Earth is because of its low sulfur-water ratio. For Earth to have both such a low ratio and a relatively thin atmosphere is nothing short of miraculous. Earth’s sister rocky planets, Venus and Mars, help highlight Earth’s amazingly benign conditions for life. Venus, like Earth, is sulfur poor, but it has no water and, despite being less massive than Earth, its atmosphere is ninety times more massive than Earth’s. Mars has a thin atmosphere but the Mars Exploration Rover Missions, Spirit and Opportunity, have confirmed and greatly extended the evidence for the dominant role of sulfur in Mars’ geochemical processes.1 Astrobiologists now acknowledge that the high sulfur-water ratio on Mars is toxic, which rules out any naturalistic origin-of-life scenario.
Astrobiologists now also understand how Mars attained its high sulfur-water ratio. For any rocky planet, its crustal sulfur-water ratio is dictated by three factors: planetary accretion resources, the degree of core formation, and igneous evolution. Earth accreted less sulfur than Mars and most of the sulfur it did accrete—because of some extraordinary mass collision events—got incorporated into the planet’s interior.2 Those same extraordinary mass collision events also explain how Earth, as massive as it is, ended up with such a thin atmosphere.3
The lander missions on Mars and Venus illuminate a Christian apologetics principle. They demonstrate that the more we learn about the physics and chemistry of other planets, the more evidence we accumulate for the supernatural, super-intelligent design of Earth for the benefit of all life, both simple and complex.