The Case for a Creator - Lee Strobel [96]
“The moon also helps in another crucial way, which is to increase our tides. The moon contributes sixty percent to the tides; the sun accounts for the other forty percent. Tides serve an important role by flushing out nutrients from the continents to the oceans, which keeps them more nutrient-rich than they otherwise would be. Scientists discovered just a few years ago that the lunar tides also help to keep large-scale ocean circulation going. That’s important because the oceans carry a lot of heat, which is necessary to keep the temperature of the higher latitudes relatively mild.”
I asked, “What if the moon were larger than it is?”
“If it were more massive and in the same place, the tides would be much too strong, which would create serious difficulties. You see, the moon is slowing down the Earth’s rotation. The tides pull on the Earth and slow it down a little bit, while at the same time the moon moves out in its orbit. We can actually measure this. Astronauts left mirrors on the moon and astronomers have been bouncing lasers off them since the early 1970s. They’ve documented that the moon is moving out in its orbit at 3.82 centimeters a year.
“If the moon were more massive, it would slow down the Earth much more. That would be a problem because if the days became too long, then you could have large temperature differences between day and night.”
James Kasting, a professor of geosciences and meteorology at Pennsylvania State University, has confirmed that “Earth’s climatic stability is dependent to a large extent on the existence of the moon.” Without the moon, he said, the Earth’s tilt could “vary chaotically from zero to eighty-five degrees on a time scale of tens of millions of years,” with devastating results.
To me, it was amazing enough that the moon “just happens” to be the right size and in the right place to help create a habitable environment for Earth. Again, it was piling on more and more “coincidences” that were making it harder to believe mere chance could be responsible for our life-sustaining biosphere.
But then Kasting made one more intriguing observation that adds yet another mind-blowing improbability to already extraordinary circumstances. “The moon is now generally believed to have formed as a consequence of a glancing collision with a Mars-sized body during the later stages of the Earth’s formation,” he said. “If such moon-forming collisions are rare . . . habitable planets might be equally rare.” 37
THE DANGERS OF A WATER WORLD
Having explored the moon’s contribution to the Earth’s life-support system, I decided it was time to focus on our planet itself. I had studied enough geology to know that the Earth is more than just an undifferentiated spinning rock, but that its interior is a dynamic and complex system eight thousand miles in diameter, with a solid iron core surrounded by iron that has been rendered liquid by the heat. At its center, where the pressure is more than three million times greater than at the planet’s surface, temperatures soar to nine thousand degrees Fahrenheit.
“What,” I said to Gonzalez, “are some of the phenomena on Earth that contribute to its ability to sustain life?”
“First let’s talk about the Earth’s mass,” Gonzalez said. “A terrestrial planet must have a minimum mass to retain an atmosphere. You need an atmosphere for the free exchange of the chemicals of life and to protect inhabitants from cosmic radiation. And you need an oxygen-rich atmosphere to support big-brained creatures like humans. Earth’s atmosphere is twenty percent oxygen—just right, it turns out.
“And the planet has to be a minimum size to keep the heat from its interior from being lost too quickly. It’s the heat from its radioactive decaying interior that drives the critically important mantle convection inside the Earth. If Earth were smaller, like Mars, it would cool down too quickly; in fact, Mars cooled down and basically is dead.”
“What if the Earth were a little more massive than