The Cosmological Improbability of You, Part 2

In my last column, I noted that some astronomers claim there may be a million or more other civilizations in the Milky Way, that we live in a galaxy rioting with consciousness.

It’s possible, I suppose.

But as the Italian physicist Enrico Fermi asked - in what is now known as The Fermi Paradox - if there are thousands or millions of other technologically advanced civilizations out there, why haven’t we heard from them? Why aren’t they here?

Where are they?

Many scientists presume that the same natural processes that occurred on Earth must have happened elsewhere in the cosmos. And, indeed, there is a lot of turf out there (surrounded by unimaginably vast stretches of nothing). Yet - despite the existence of hundreds of billions of other galaxies and stars - extraterrestrial life is still a big presumption.

There is no good evidence for it.

What is missing from the science of exobiology is a sample of the stuff. As one wag put it, the only constant in the search for alien life is nothing happens.

Of course, we’ve only been scanning the heavens for 50 years. We may find something eventually.

Or it could be that nothing is there, that life here is the miracle of miracles, the result of countless unforeseen contingencies. If so, we are incalculably fortunate to be here.

Consider the Earth. It is just the right distance from the sun. Venus is a boiling mess. Mars is a frozen desert. But you and I are here because our planet inhabits what scientists call “The Goldilocks Zone,” a region where temperatures are moderate and water can exist as a liquid.

If the Earth were 5% closer to the sun or even 1% farther away, the planet could not maintain a habitable biosphere. (And what a biosphere it is with, for instance, animals breathing in oxygen and releasing carbon dioxide and plants doing just the opposite.)

Countless other circumstances work to our advantage. For example, without a massive planet like Jupiter nearby, whose gravity draws away asteroids, a thousand times as many would hit Earth’s surface.

Many have in the past. Consider “The Big Splash.”

About 4.5 billion years ago, a proto-planet about the size of Mars smashed into the planet. Its dense metallic core sunk into the Earth helping create our strong magnetic field, an essential factor in providing conditions suitable for life.

The collision also blasted trillions of tons of debris into space, creating the moon. (To see a National Geographic dramatization of this event, click here.)

The gravitational effect of the moon stabilizes the Earth and affects the tides. Plants, and eventually animals, made the transition onto land by spreading out from the tidal zones.

The glancing blow of The Big Splash also knocked the Earth at an angle, creating the planetary tilt that gives us our seasons. And it set the Earth spinning much faster. (Venus takes 243 of our days - not 24 hours - to rotate once on its axis.)

The collision created the continental plates. If they didn’t glide over the mantle - the rocky inner layer above the core - the Earth couldn’t sustain a surface temperature in the range required for the existence of liquid water. And without water, the chemical interactions on which our lives depend would not be possible.

Think about it. That single cosmic accident is responsible for the moon, the tides, the planet’s rotation, the seasons, our magnetic field, continental drift and, ultimately, life on Earth.

And that was just one contingency.

Five others are the major extinctions that happened along the way, including the Ordovician (440 million years ago), the Devonian (365 million years ago), the Permian (245 million years ago), the Triassic (210 million years ago) and the Cretaceous (65 million years ago).

The real whopper was the Permian, when at least 95% of animals known from the fossil record became extinct. Even a third of the generally hardy insect species were lost. It was the closest life on this planet has come to total obliteration.

Of crucial importance was the Cretaceous extinction 65 million years ago. That’s when a 6-mile-wide asteroid or comet struck the Yucatan Peninsula and caused the extinction not just of the dinosaurs but of three-quarters of all species on Earth. That event allowed our distant ancestors to gain a toehold. (Mammals found it much tougher when 90-ton reptiles ruled the planet.)

Nobody knows exactly how many species have existed on Earth since life began. Some put the number as high as 4 trillion. But we do know this: 99.99% of them are gone.

Extinctions happen. On Earth, death is a way of life. For complex creatures, the average life span of a species is about 4 million years. That’s roughly where we are now.

How do you calculate the odds of life arising on Earth? You can’t. That’s why we can’t even guess about its probability elsewhere.

Scientists have already enumerated 200 known parameters necessary to support life on Earth - every single one of which must be perfectly met, or the whole thing falls apart.


We should be humbled by what natural history reveals - but humbled more by what we still don’t know.

I’ll discuss some of those things in my next column.

Carpe diem,


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