There is no question in all of science that is more perplexing, and more difficult to answer, than this simple query: How did life on Earth begin? It happened so long ago, when the planet was still in its infancy, that most of the evidence has vanished, leaving scientists with little hope of ever finding the answer.
But that may be changing. Scientists, disenchanted with an 80 year old theory that life began in a "primordial soup," are focusing on deep-sea pressure cookers that were unknown just a couple of decades ago. Life may well have begun in tiny "chimneys" in a green rock that is common on earth, as well as other celestial bodies, when the ocean was 100 times more acidic than it is today, and the planet was much warmer.
Serpentine, California's official state rock, is on center stage today as a possible major player in generating the first life on Earth, more than 3.8 billion years ago.
This green stone, which looks a lot like jade, could have been a "rich incubator" of the unicellular life that first flooded the earth so long ago, according to geophysics professor Norm Sleep of Stanford University. Sleep didn't invent the idea of serpentine as an incubator, but he set out to learn if the theorizing of biologists could survive a geological inquiry. Were the geological conditions of early Earth compatible with life originating in serpentine?
Two of his colleagues, Dennis Bird and Emily Pope, mounted an expedition to Greenland, where they found serpentine rocks in some of the oldest formations on the planet, at least 3.8 billion years old. So serpentine would almost certainly have been plentiful when first life appeared. Furthermore, other critical components were also present, leading to this cautious assessment by Sleep during a telephone interview:
"It's reasonably viable" that life first appeared in tiny pores in serpentine, buried deep below an acidic ocean, he said. But the conditions didn't last forever, probably no more than a few million years. That's a small window for a geologist, accustomed to thinking in terms of eons, but it may have been long enough for biologists.
"We can't prove it's right," Sleep added, "but we can prove it's reasonable."
'Primordial Soup'? Maybe Not
For more than eight decades, an essay by J. B. S. Haldane dominated the theory of the origin of life, suggesting that a murky pond, energized by ultraviolet rays from the sun, produced the first life on earth. But that's not enough energy, and other conditions aren't met, leading a growing number of scientists to look for another answer.
Nick Lane of the University College London wrote a paper disputing Haldane's essay and offering a new theory.
"That old and familiar view won't work at all," Lane said when he released his study last year. "The energy for first life came from harnessing geochemical gradients created by mother Earth at a special kind of deep-sea hydrothermal vent, one that is riddled with tiny interconnected compartments or pores."
For four decades now scientists have been fascinated by deep ocean vents, called black smokers, that spew toxic chemicals into the sea, but still harbor strange animals, including giant tube worms. But that's not the kind of hydrothermal vent Lane was talking about.
Deep-Sea 'White Smokers'
In 1993, Michael Russell of NASA's Jet Propulsion Laboratory postulated that the sea floor probably has other vents that are not nearly as hot as the black smokers, and would therefore be more conducive to generating life. Seven years later, "white smokers" were discovered on serpentine rocks deep in the Atlantic Ocean.
The white smokers had it all -- not so hot that any organic substances would be destroyed, and having an abundance of chemicals that could form the nucleic acids favorable for life. And equally important, these miniature volcanoes had plenty of energy.
Serpentine also supplied the answer to a question scientists have been raising for decades. It's sort of a chicken and egg question. Which came first, a living cell, or a membrane to house the cell? It's hard to see how a membrane could form before the living cell, but how does the cell hold itself together until it can form a membrane?
Serpentine is riddled with tiny pores, in which alkaline fluids interact with acidic seawater -- another source of energy -- and these pores probably serve as a natural home for the acids that are necessary for the formation of RNA, essential for all forms of known life.
"Organic matter will collect on the sides of these micropores," Sleep said, so the pores themselves could serve as a cell membrane until the cell makes its own membrane and is ready to leave the incubator. And leave it must, because the chimneys collapse in a few years, and that's a good thing.
"Life needs to disperse," says Sleep's paper, published in the Philosophical Transactions of the Royal Society B.
"It will just proliferate and multiply and inhabit every reachable habitat on the earth that it can live in," Sleep added in the interview.
According to this theory, it wasn't necessary for life to travel to this earth from Mars or outer space, as NASA has suggested. It could have originated here, and possibly throughout the universe.
"Life originates quickly, so that's a hint that it originates easily," Sleep said, noting that it didn't take long after the earth cooled and became hospitable for life that life did, indeed, appear.
It's an interesting theory, and fascinating research, but when will we know if it's correct?
"The geological record is gone, unless we get darn lucky," Sleep said.
We can't recreate the Earth as it existed nearly four billion years ago. Proving this theory will be very difficult. But maybe somewhere there's a rock, or a crystal, with clues that, for the moment, we know nothing about. That would be very, very lucky.