Life gets going whenever and wherever it possibly can
Three and a half billion years ago, as a huge moon circled much closer to Earth than today, raising enormous tides of scalding water, and in a poisonous atmospheric mix of methane gases, something amazing, mysterious, but perhaps entirely common happened: Life appeared.
Only 300 million years earlier, the Earth had been a roiling mass of molten rock and steam, constantly bombarded by asteroids and continually sterilized by ferocious heat.
But slowly, as the Solar System’s cosmic vacuum cleaner we call Jupiter swallowed up more and more of those roving asteroids, the bombardment drew to a close and our planet began to settle down. As the oceans began to cool to the temperature of a hot bath, a beach formed on the edge of an island that had emerged from the water in a region we now call Australia. And bacteria began to grow.
A few weeks ago, scientists who had been studying microfossils in Western Australia said they were confident they’d found the world’s oldest known fossils – formed 3.4 billion years ago. For several years there’s been hot debate over fossils like these: Are they truly the remains of bacteria or are they something else altogether? What is now beyond doubt, however, is that whether it was 3.4, 3.5 or even possibly 3.8 billion years ago, life started taking hold on Earth in the proverbial blink of a geological eye, just as soon as it conceivably could when the Late Heavy Bombardment of asteroids came to an end.
Not that everything was peachy for the emerging new world of living things. At least five great extinction events have happened since then: some caused by fire, others by ice. One of them, set in motion by huge volcanoes about 400 million years ago, obliterated all the creatures in the ocean, along with the few plants and tiny insects that had begun to develop on land. It took another 10 million years or so before life could once again take hold. But it did – then and every other time.
What does this primordial history suggest about the nature of life?
Back in the 1970s, a famous debate took place between astrobiologist Carl Sagan and zoologist Ernst Mayr over the likelihood of intelligent life having taken hold elsewhere in the universe. Sagan argued that among the enormous number of Earth-like planets, at least a few, and probably a very large number, must have given rise to intelligent life. Mayr countered that among all the millions of species ever to take hold here on Earth, only one has ever evolved to the point of being able to do things like having this debate – at least as far as we know.
But Sagan and Mayr, along with most astrobiologists today, agreed that life itself was almost certainly not unique to Earth.
“There is no argument between Carl Sagan and myself,” Mayr said, “as to the probability of life elsewhere in the universe.”
That probability has only become stronger with the discovery of the latest microfossils in Australia. Just as soon as conditions permitted, life on Earth began. And despite repeated mass extinctions, it kept bouncing back – again and again. (And from what we’ve been learning from observations on Mars, it’s looking increasingly like, at very least, the conditions for life once existed there, too.)
Life is tenacious. It’s pushy. It wants to be. All the signs we have point clearly to the conclusion that the universe is friendly to life, and that we on this planet are not alone.
Today, with at least five great extinction events already behind us, Earth has now entered a sixth. Of the 8.7 million species recently estimated to exist on the planet, about 50,000 will disappear this year. And the number is rising alarmingly each year.
This time, it’s not because of asteroids, volcanoes or sudden cooling. This time, the extinction is being driven by living creatures: us. And while even the most dramatic of the earlier extinctions – the asteroid strike that wiped out the dinosaurs – took thousands of years to run its course, the current extinction is taking place at a breakneck pace, like nothing in our planet’s history.
Within just a few decades, we will most likely have seen the last of some of the animals in the wild that we say we love the most, including the elephants and tigers and polar bears and gorillas. Gone, too, will be the coral reefs that are the birthing places of most of the fish in the oceans.
Whether or not we come to our senses and take action to mitigate the disaster that’s unfolding, life will go on. It may re-emerge in as different a form as it did after each of the previous extinctions, just as the decline of the dinosaurs led to the rise of the mammals – and eventually us. While Carl Sagan didn’t doubt that intelligent life could emerge on other worlds, the question he kept asking was whether it could survive its “teenage” phase of self-destructiveness – the very phase we’re going through right now.
With or without us, and with or without the other animals we take down with us, life itself will surely recover. It will take whatever form it can, in whatever environment it finds itself.
The Earth is still young – just a few billion years old – in a universe that has trillions of years yet to go. In that perspective, we’re barely a grain of sand on the vast expanse of space and time.
That may be sound a bit disconcerting to you and me. But in its own way, it’s mildly comforting to know that whatever damage we’re doing to ourselves and the other animals, life itself is far more powerful than we are.
Meanwhile, elsewhere in our own galactic neighborhood, on a planet that’s just beginning to settle down from its fiery birth, the earliest elements of life are probably just beginning to form. A few billion years from now, who can imagine what they will have become? Maybe, depending on how we behave over the next few decades, our own descendants will be around to witness what happens in that future.
Then again, maybe not.