The Case for a Creator - Lee Strobel [97]
“The bigger the planet, the higher the surface gravity, and the less surface relief between the ocean basins and the mountains,” he said. “The rocks at the bases of mountains can only withstand so much weight before they fracture. The higher the surface gravity of a planet, the greater the pull of the gravity on the mountains, and the tendency would be toward creating a smooth sphere.
“Think what would happen if our planet were a smooth sphere. The Earth has a lot of water in its crust. The only reason we’re not a water world right now is because we have continents and mountains to rise above it. If you were to smooth out all the land, water would be at a depth of two kilometers. You would have a water world—and a water world is a dead world.”
That perplexed me. “If you need water for life,” I said, “why doesn’t more water mean more life?”
Gonzalez replied, “We have life on Earth because we have the energy-rich sunlit surface of the oceans, which is teeming with mineral nutrients. Tides and weathering wash the nutrients from the continents into the oceans, where they feed organisms. In a water world, many of the life-essential minerals would sink to the bottom. That’s the basic problem. Besides, the salt concentration in a water world would be prohibitively high. Life can only tolerate a certain level of saltiness.”
“Our oceans and seas are salty,” I said. “How does Earth manage to regulate this?”
“We have large, marshy areas along some coasts. Because these are shallow, water comes in from the ocean and evaporates quickly, leaving salt behind. So you get huge salt deposits accumulating on the continents, and the salt content of the ocean doesn’t get out of control. But in a water world, eventually the excess salt would saturate the water and settle to the bottom. This would create a super-saturated salt solution that would be inhospitable to life.”
Even so, I said, some scientists have theorized that life might exist inside Jupiter’s frozen moon Europa, where a theoretical ocean might be located. “It doesn’t sound like you think life would be possible in an environment like that,” I said.
“No, I don’t think so,” he replied. “I don’t believe it would be habitable. There would be no way to regulate the salt, so I certainly don’t imagine there are any dolphins swimming around in there.”
Mountains and continents, then, are crucial for a life-flourishing planet. But where did they come from? I soon learned that they are partly the product of elaborate choreography involving radioactive elements and plate tectonics—absolutely essential ingredients for any planet to sustain a thriving biosphere.
THE ENGINE OF THE EARTH
Scientists over the last several decades have established the surprising centrality of plate tectonics, and the related continental drift, to the sustaining of life on Earth. Continental drift refers to the movement of a dozen or more massive plates in the Earth’s lithosphere, which is the outer, rigid shell of the planet. One crucial byproduct of plate tectonics is the development of mountain ranges, which are generally created over long periods of time as the plates collide and buckle.
Scientists are finding that the importance of plate tectonics is difficult to overstate. “It may be,” said Ward and Brownlee in Rare Earth, “that plate tectonics is the central requirement for life on a planet.” 38 Interestingly, they added that “of all the planets and moons in our solar system, plate tectonics is found only on Earth.” 39 In fact, any heavenly body would need oceans of water as a prerequisite to having plate tectonics, in order to lubricate and facilitate the movement of the plates.
When I asked Gonzalez why plate tectonics is so crucial, he launched into describing an improbable series of highly coordinated natural processes that left me amazed once more at how finely tuned our planet really is.
“Not only does plate tectonics help with the development of continents and mountains, which prevent a water world, but it also drives the Earth’s carbon dioxide–rock cycle,” he said. “This