It is among the most profound of questions.
If proven, the existence of life elsewhere even–primitive life–would be the greatest scientific discovery of the century. It could shock the human psyche so much that we would lose our reference point–the very way we think about ourselves and our place in the cosmos.
If life is not unique to this planet, the possibility of advanced life elsewhere isn’t either. Only within the last year have scientists abruptly found themselves in the position of being able to start asking real questions.
With stunning suddenness, tantalizing evidence is coming from research findings that are dramatically expanding our understanding of what it takes to create life–understanding that may get a big boost next Thursday when the Galileo spacecraft makes its closest approach to Jupiter’s moon Europa and tries to spot an ocean that could possibly harbor Big News.
Not long ago, many researchers thought that the first thing to live on Earth had to be coddled in a primeval womb so perfect that it really was a cosmic accident. Such a coincidence is so improbable that it is likely never to be repeated.
We are alone, they insisted.
What it took for life to be generated was something like Darwin’s warm little pond–water, along with sunlight, mild temperatures, oxygen or carbon dioxide, and abundant chemical nutrients. The sun, it was said, was the life-giver because plants used it to grow, thereby providing the first link in the food chain that animals depend upon.
But that was before the discovery of nature’s “Dead End Kids”–organisms that could live under such extraordinarily harsh conditions that they thumbed their noses at all the old notions about what it takes to really be alive.
These tough life forms were found thriving in perpetual blackness at the bottom of the ocean, and in boiling geysers, and in the permanently frozen ice of Antarctica, and miles under the Earth’s surface.
Some of the tiny creatures, a family called Archaea, after years of scientific debate, have been accorded status as a brand-new branch on the tree of life.
Genetically identified for the first time only last summer, Archaea are turning out to be all around us. In fact, they may be the most direct descendent of the first life forms on the planet.
Half of the Archaea genes are unique, never seen before, indicating that they went their separate ways long ago. They share the other half with the two other main branches of life–Prokarya (bacteria and other single-celled organisms) and Eukarya (all plants and animals, including humans).
By sheer mass, Archaea along with hardy bacteria, which also have been found everywhere, ranging from deep within our bowels to deep in the ocean floor, make up the majority of life on Earth. Most species exist in total darkness and in places where free oxygen, so essential to life on the surface, is non-existent. In fact, free oxygen would kill them.
That there was this vast subterranean population came as a shocker. It revealed how little scientists really knew about life on this planet, let alone other worlds.
“The surface of the Earth isn’t much compared to what’s under it,” said the noted evolutionist Carl Woese of the University of Illinois at Urbana-Champaign.
“I’ve always had the feeling that the microbial world is a much bigger place than we thought,”said Woese, who 19 years ago was branded a heretic for proposing the existence of Archaea.
It turns out that we have been looking for life in all the wrong places. In fact, the hospitable conditions that exist on the Earth’s surface, where sunlight produces energy through photosynthesis, may be rare indeed.
But the newly found underworld of microscopic organisms, which get their energy by gobbling a witches’ brew of hot chemicals, suggests that this kind of life may be prevalent in our solar system and the rest of the universe.
So, instead of looking for sun-dappled watery paradises, we should be looking for life in hot, dark places. Those are the places, like the volcanic vents at the bottom of the oceans, where the story of life on Earth probably began. Such vents pop up where molten material from the interior pushes up to form new sea floor.
“Life is a natural phenomenon written into the fabric of the universe,” contends Nobel laureate Christian de Duve, emeritus professor of cellular biology at Rockefeller University.
De Duve shifted his science in a new direction by discovering certain key structures inside cells that allowed them to survive and prosper.
“We live in a cosmos that is made in such a way that given the right conditions, life will come,” he said in a recent talk to medical students at Northwestern University.
Some of the conditions began to make themselves apparent this year.
The Galileo spacecraft radioed back pictures of what looks like ice-covered oceans on Jupiter’s moon Europa; the eye-popping Hubble Space Telescope captured planets revolving around other stars; and a radar-bouncing probe identified what may be a frozen lake on the moon.
Europa is particularly exciting because it may have had liquid water for more than four billion years. It is also likely to have an internal source of heat, just like its pizza-faced satellite neighbor, Io, on which volcanoes are erupting all the time.
“If processes that we see taking place on Earth occur on Europa, then the next question is: Have they resulted in the production of life?” said John Delaney, a University of Washington marine geologist who dives to the bottom of the ocean in research submarines to study life around volcanic vents.
We need to send a probe crashing into Europa, as we did Jupiter. Finding living creatures there–even the most primitive Archaea–would tingle the spine of every human on Earth.
The most startling discovery continues to amaze and confound. NASA scientists contend they had detected evidence of early life on a 3.6 billion-year-old rock exploded by a comet or asteroid collision from the interior of Mars and eventually plunking down in Antarctica, where a scientist picked it up 13 years ago.
“There are four different kinds of observations that when taken together point to this biological explanation of the fossilized structures in the Martian meteorite,” said Wendell Mendell, a planetary scientist at the Johnson Space Center in Houston.
“They probably have the greatest potential for answering `Are we alone?’ Obviously that has tremendous philosophical importance.”
Thomas Gold, emeritus professor of astronomy at Cornell University, suggested four years ago that the Martian rocks should be studied to look for signs of life. He even predicted what hints would remain if Mars had microbes.
Without free oxygen, such as that which exists in our atmosphere, microbes have to chomp apart minerals to liberate their oxygen, which they then burn to produce energy.
Next to what looks like fossilized bugs a millionth the size of a pinhead in the Mars rocks, scientists think they found what Gold predicted: Sulfur and iron compounds robbed of their oxygen. In other words, something ate the oxygen.
“Are we alone? Certainly not,” says Gold, who believes that there are at least 10 other planets or their moons in our solar system that could harbor microscopic life. “It’s pretty clear that living material, at least in the form of microbes, is pretty common.”
Putting all the discoveries together suggests that the ingredients for creating life are varied and abundant and that nature has a great urge to match them up.
Indeed, life may be inevitable, given the laws of physics and chemistry that make elementary particles seek out each other to form atoms, and atoms attract other atoms to form molecules. Driven by a variety of energy sources, molecules then combine in increasingly complex arrays until self-replicating life forms are created.
“Life is chemistry,” explained De Duve. “Our bodies keep running because of thousands of chemical reactions going on each instant. Life arose by the formation and self-organization of chemical substances of increasing complexity.
“Chemistry is not serendipity. When you mix A and B, you always will get C.”
Furthermore, astronomers have found that the universe is filled with carbon-based chemicals, just like the ones that Earth-based life depends on. The chemical building blocks were discovered in gigantic dust clouds, the birthplace of stars and planets, and on meteorites.
“They are there,” said De Duve. “And they’re ready to participate in more complex synthetic reactions, if given the opportunity.”
Although the evidence for life elsewhere continues to mount, more proof is required. A U.S. spacecraft is en route to study Mars, but it is not specifically designed to test for signs of life. The evidence has mounted too quickly, too suddenly.
What is needed is a probe that can retrieve rocks torn up from deep within the planet or from riverbeds that were eroded long ago when Mars had water, and bring them back to Earth. Such a mission is planned for 2005, but with the new interest sparked by the new evidence, the mission could be speeded up, possibly to 2000.
In the meantime, scientists are grappling with findings suggesting that life started rather quickly on Earth after its formation about 4.5 billion years ago.
The fossilized remains of bacteria that date back 3.8 billion years have been located in Australia, and they look remarkably similar to microscopic bugs that are alive today.
“Vast numbers of bacteria have been found thriving around underwater volcanoes, which have the youngest, hottest rocks on this planet,” said Delaney.
“That’s a big surprise,” he said. “That means that volcanoes– independent of the sun–can support life.
“That single theme is a major guide to where to look in the solar system and beyond. That may be the environment that is most optimal.”
What about intelligent life?
“The probability of finding intelligent life somewhere else is a lot lower than the probability of finding life itself,” Delaney said.
“After all, Earth has been a microbial planet for at least 3.8 billion years. And we humans? We’ve only been around a couple million.”
