Part 2: Life on Earth depended on luck


By Tom Burns - Stargazing



Last week, we discussed some of the fortunate events that led to life on planet Earth. We have been lucky indeed. Will our luck run out? Are we pressing our luck?

We left the planet early in its formation. It was a pretty nasty place by current standards — a hot ball of rock with a large quantity of water on its surface and a rich chemical mix in its atmosphere and oceans.

Earth cooled very slowly, which was another bit of luck.

Like all the planets, Earth was created from a series on violent collisions of smaller objects called planetesimals. Earth has maintained a very thin crust with still-hot, molten rock underneath. The same is not true for mostly solid Mars, which is also within the life-friendly Goldilocks Zone.

Earth’s interior is still hot and liquid in part because of a relatively lucky abundance of radioactive elements. Their decay produces heat energy, and that energy comes in handy where life is concerned.

One thing is certain — life needs energy. Although the issue is controversial, an increasing number of scientists are persuaded that life probably originated deep under the sea. At points where the crust is thinnest, hot rock from the interior seeps to the surface. The first life fed on the energy released by those steamy vents in Earth’s crust.

In fact, Earth’s solid crust isn’t very solid at all. Its outer layer is really a set of large “islands” of solid crust floating on the liquid crust below. We have found no evidence that such moving plates exist anywhere in the solar system. Again, our planet is lucky in that regard.

Earth’s innards are also churning around, which is responsible for Earth’s magnetic field. Deep at its center, Earth contains a heavy iron core in two layers, a central core and an outer core surrounding it. The deepest part of the iron core rotates very slowly or not at all. Earth’s rapid rotation causes the outer iron core to rotate more rapidly than the inner core. As they rub together, they generate a magnetic field, which is made even more powerful by the churning that occurs in Earth’s rocky middle layer, its mantle, as heat rises from the iron core.

Our magnetic field is a lucky break for us. Earth’s twin in terms of size, the planet Venus, is also within the Goldilocks Zone, but Venus doesn’t have a magnetic field, probably because it rotates too slowly.

The magnetic field captures deadly charged particles that erupt from the sun’s surface. It diverts them before they strike the planet and carries them along lines magnetism to the poles. From there, they stream harmlessly though the atmosphere and cause the spectacular aurorae visible from northern climes.

In a very real sense, our magnetic field is a shield against those solar particles and thus made it possible for life to migrate from the oceans to the solid surfaces of the Earth.

At some point, the simple life created in the oceans developed an almost miraculous skill. Plants evolved beyond their ability to use heat from ocean vents. Plant life developed the ability to turn sunlight into energy it can use to create its substance. We call that astounding process photosynthesis.

Plant life still needed the oceans for protection because sunlight was still deadly. The high-energy ultraviolet energy from the sun would kill you now except for another bit of luck.

Photosynthesis uses the sun’s energy to break down the planet’s supply of carbon dioxide to get at its carbon. The process produces oxygen as a corrosive byproduct.

As sunlight hits the oxygen in the upper atmosphere, oxygen is converted to ozone. And ozone provides a pretty effective shield again the harmful ultraviolet component of sunlight.

Oxygen has another vital effect. It makes possible the development of a new kind of living organism. Animal life produces the energy it needs by burning, the slow reaction of oxygen with other forms of organic material.

Rapid oxidation releases energy quickly. We call it “fire.” Slow oxidation produces energy at a much more systematic pace — at just the right rate to produce the energy that animal life needs without destroying it.

When animal life moved to the solid surface, it was thus well protected against the deadly effects of the sun. Slowly, it developed both an abundance of species and the ability of successful species to propagate.

Still, many species failed sooner or later because they could not adapt to the ever-changing circumstances of Earth’s environment.

The kings of such complexity, adaptability, and longevity (in larger animals, at least) were the dinosaurs, which populated Earth for perhaps 175 million years. They might still rule the Earth instead of humans but for another bit of luck.

About 65 million years ago, an asteroid only six miles wide struck our planet. Combined perhaps with a contemporary flurry of volcanic activity, the resulting explosion filled the planet’s atmosphere with a thick layer of dust, which blocked the sun’s light for as much as two years.

The result was a mass extinction of species. Without sunlight, the plants that the herbivorous dinosaurs ate died. The dinosaurs that ate the herbivorous dinosaurs died.

The extinction of the dinosaur species proves the old saying: “Bad luck for somebody is always good luck for somebody else.” The death of the dinosaurs made room for a tiny shrew-like mammal that would develop eventually into humans.

How lucky we have been, but our luck could run out at any time.

Another giant impact could create the same kind of long winter that would destroy our food sources. Also, we could bring such a nuclear winter upon ourselves. The result of global thermonuclear conflict would kill off a substantial number of humans in the explosion and subsequent radiation. The long winter would kill off the rest.

Thank goodness that the most recent phase of the development of life does not depend so much on luck. One of the characteristics of life is its growing ability to gather information and use it for its own survival and the survival of its species. This trait we call “intelligence.”

A simple bacterium does so in a very limited way. It developed the ability to notice heat. It developed the biological tool to deal with it in the form of fine cilia. It “thinks,” “It’s too hot here. Swim away!” In other words, it gathers information about its environment and uses it to adapt to that environment.

Humans have developed such intelligence to its highest degree so far. We also developed the physical tools to adapt better to environmental changes. Our opposable thumb, for example, gave us the ability to create tools.

An individual can gather only so much information, so we developed methods of communication to transmit it to others.

Our brains can hold and process only so much information, so we developed computer that can, on limited subjects, do a better job of gathering, processing, and transmitting information than we can.

Such talents have their price, however, and the price can be steep. As we modify the environment to suit our perceived needs, we also alter its delicate balance.

In that regard, we may be pressing our luck.

I’m not going to get into the question of whether humans are the cause of rising temperatures and climate change. However, certain facts remain.

1. Climate change causes the death of species at a rapid rate. Organisms are designed to work within a set of environmental parameters. If those conditions change too much or too rapidly, species are eliminated at a rapid rate. The result is that the environmental niche that dinosaur extinction created for us may disappear.

2. There are simply too many of us. The superb science writer Isaac Asimov once commented that all of the problems of our species could be summed up in three words: “Too many people.” We are in danger of exhausting the very resources that made the growth of humanity possible.

3. Global temperatures are rising. Our failure to do something about that could indeed upset the delicate environmental balance that makes humanity possible.

In fact, those outcomes may already be happening. We are in the midst of a mass extinction right now. Biologists estimate that we are losing 114 times the species than we do in times between mass extinctions, and the rate is increasing. The loss is connected with deforestation and the loss and fragmentation of species habitat. Humans are mostly responsible for both.

I’m not going to interpose myself into the climate-change debate except to say this: Climate change and a mass extinction may or may not be connected, but they are certainly happening. If humans are not the cause of climate change, they are almost certainly accelerating the process.

In fact, I feel a certain sympathy for those who don’t believe that this is so. Whatever the cause, climate change and mass extinctions will eventually weaken the bottom of a food chain we depend on for our existence as a species. For the climate-change deniers, there is absolutely nothing that can be done to stop the process.

I may be wrong, but I’d like to think that we have erred and that we have the ingenuity and will to correct our mistakes before it is too late. According to a recent UN report, we have only 10 years to engage in that herculean task. Let’s get crackin’.

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By Tom Burns

Stargazing

Tom Burns is the former director of the Perkins Observatory in Delaware.

Tom Burns is the former director of the Perkins Observatory in Delaware.