The Case for a Creator (30 page)

“What would happen,” I asked, “if the moon were not there?”

“Then our tilt could swing wildly over a large range, resulting in major temperature swings. If our tilt were more like ninety degrees, the north pole would be exposed to the sun for six months while the south pole would be in darkness, then vice-versa. Instead, it varies by only about one and a half degrees—just a tiny variation, because the gravity from the moon’s orbit keeps it stabilized.

“The moon’s large size compared to its host planet is unique in the inner solar system,” he continued. “Mercury and Venus have no moons. Mars has two tiny moons—probably captured asteroids—and they don’t do anything to stabilize the axis of Mars. Its axis is pretty close to Earth’s right now, but that’s only by coincidence. It actually varies over a huge range. In fact, all three of these planets have chaotic variations in their tilt.

“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.”
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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 it is?” I asked.

“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.”
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Interestingly, they added that “of all the planets and moons in our solar system, plate tectonics is found only on Earth.”
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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 is critical in regulating the environment through the balancing of greenhouse gases and keeping the temperature of the planet at a livable level.

“You see, greenhouse gases, like carbon dioxide, absorb infrared energy and help warm the planet. So they’re absolutely crucial. The problem is that their concentration in the atmosphere needs to be regulated as the sun slowly brightens. Otherwise, the Earth would not be able to stabilize its surface temperature, which would be disastrous.

“Plate tectonics cycles fragments of the Earth’s crust—including limestone, which is made up of calcium, carbon dioxide, and oxygen atoms—down into the mantle. There, the planet’s internal heat releases the carbon dioxide, which is then continually vented to the atmosphere through volcanoes. It’s quite an elaborate process, but the end result is a kind of thermostat that keeps the greenhouse gases in balance and our surface temperature under control.

“What’s driving plate tectonics is the internal heat generated by radioactive isotopes—Potassium-40, Uranium-235, Uranium-238, Thorium-232. These elements deep inside the Earth were originally produced in supernovae, and their production in the galaxy is declining with time because the supernova rate is declining with time. That will limit the production of Earth-like planets in the future, because they won’t generate as much internal heat as the Earth does.

“This radioactive decay also helps drive the convection of the liquid iron surrounding the Earth’s core, which results in an amazing phenomenon: the creation of a dynamo that actually generates the planet’s magnetic field. The magnetic field is crucial to life on Earth, because it shields us from low-energy cosmic rays. If we didn’t have a magnetic shield, there would be more dangerous radiation reaching the atmosphere. Also, solar wind particles would directly interact with the upper atmosphere, stripping it away, especially the molecules of hydrogen and oxygen from water. That would be bad news because water would be lost more quickly.

“Now, remember how I said that plate tectonics helps regulate global temperatures by balancing greenhouse gases? Well, there’s also another natural thermostat, called the Earth’s
albedo
.
Albedo
refers to the proportion of sunlight a planet reflects. The Earth has an especially rich variety of albedo sources—oceans, polar ice caps, continental interiors, including deserts—which is good for regulating the climate. Whatever light isn’t reflected by Earth is absorbed, which means the surface gets heated.

“This is self-regulated through one of the Earth’s natural feedback mechanisms. To give you an example, some marine algae produce dimethyl sulfide. This helps to build cloud condensation nuclei, or CCN, which are small particles in the atmosphere around which water can condense to form cloud droplets.

“If the ocean gets too warm, then this algae reproduce more quickly and release more dimethyl sulfide, which leads to a greater concentration of CCN and a higher albedo for the marine stratus clouds. Higher cloud albedo, in turn, cools the ocean below, which then reduces the rate at which the algae reproduce. So this provides a natural thermostat.
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“On the other hand, Mars lacks oceans, so it doesn’t have this albedo component. It only has deserts, small polar caps, and very thin, occasional clouds. So Mars is far less capable of adjusting its albedo as its more eccentric orbit takes it closer and then further from the sun. That’s one of the reasons why it experiences larger temperature swings than Earth.”

Giant plates of shifting rock that precariously balance greenhouse gases; decaying radioactive isotopes acting as a life-sustaining underground furnace; an internal dynamo that generates a magnetic field which deflects cosmic dangers; precision feedback loops that unite biology and meteorology—I had to pause and marvel at the complex and interconnected processes that orchestrate our planet’s environment.

And that was just the beginning. I knew Gonzalez could go on and on about scores of other fine-tuned phenomena. Among them are the elaborate physical processes that resulted in valuable ores being deposited near the planet’s surface, enabling them to be efficiently mined for our technological development. Geologist George Brimhall of the University of California at Berkeley has observed:

The creation of ores and their placement close to the Earth’s surface are the result of much more than simple geologic chance. Only an exact series of physical and chemical events, occurring in the right environment and sequence and followed by certain climatic conditions, can give rise to a high concentration of these compounds so crucial to the development of civilization and technology.
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When I took this together with all of the various “serendipitous” circumstances involving our privileged location in the universe, I was left without a vocabulary to describe my sense of wonder. The suggestion that all of this was based on fortuitous chance had become absurd to me. The tell-tale signs of design are evident from the far reaches of the Milky Way down to the inner core of our planet.