Q. HAVE YOU ALWAYS BEEN INTERESTED IN THE CHEMISTRY OF LIFE?
A. No. When I started in graduate school in 1965, I had ideas about becoming a theoretical chemist, applying quantum mechanics to chemistry. But when I arrived at U.C.S.D., I met Stanley Miller, who’d been a student of Nobel Prize-winning chemist Harold Urey. In 1953, they completed the classic experiment on the chemical origins of life. They’d taken gases present on the early Earth like methane, ammonia and hydrogen and applied a spark discharge to them, to mimic lightning. From that, they produced amino acids, the compounds that make up the proteins in all living organisms. It was a stunning discovery. So when I met Stanley, I was hooked. I switched my thesis to work with him. My Ph.D. idea was to move the spark discharge experiment a step forward by studying amino acid stability.
Q. WHY WAS STABILITY IMPORTANT TO UNDERSTAND?
A. Because, in the turbulent environment of the early Earth, if an amino acid had been too unstable it would have decomposed. There would have never been enough of it to make up what we call “the prebiotic soup,” the molecular ingredients of life. So I suggested this one set of reactions that might constrain their decomposition, and then, in the lab, we did an experiment, which worked the first time we tried it. We were able to show some of the conditions that would allow amino acids to exist for longer time periods. And this allowed us to understand what types of amino acids may have been present on the baby Earth.
Q. DO WE KNOW HOW THEY BECAME LIFE?
A. We are closing in on that question. The Earth had to cool down enough for water to appear. Water allows molecules to dissolve and interact, which is why it is essential to life. We do know that we went from simple molecules to more complex molecules and eventually to RNA, which evolved into DNA. This took about a billion years.
The missing piece of the puzzle is that intermediate phase between the amino acids and the RNA phase. We know that RNA is too complex to have arisen out of the simple molecules of the primordial soup. We can surmise that this intermediate form was able to make copies of itself to pass onto the next generation. Over time, mutations occurred and those mutants with survival advantages thrived and on and on until you eventually got to the complex RNA world.
Q. IS THIS SAME PROCESS AT WORK SOMEWHERE IN THE UNIVERSE NOW?
A. The chemistry we see in the lab is universal chemistry. It takes place anywhere you have the ingredients and conditions. We know that it happened, partially, on some of the meteorites that have come to earth. Amino acids have been found inside some of them.
Q. SO WE’RE PROBABLY NOT ALONE?
A. I don’t want to say “we” because people immediately think of something like a human being. But life as we know it — a self-replicating system — is probably not unique to the Earth. Under the right conditions, with the right chemistry, it can happen. There may be simple chemistry happening on Titan, a moon of Saturn. Some people think it could be happening on the satellites of Jupiter. There are compelling reasons to think that Mars was wet when it was young and that the raw materials for life could have been there. We don’t know how far it progressed.
Q. DID YOU SUPPORT FORMER PRESIDENT GEORGE W. BUSH’S PLAN FOR MANNED TRAVEL TO MARS?
A. I’m glad the Obama administration appears to be canceling it. Until we know whether or not life existed on Mars, putting humans there is premature. We’d contaminate the planet. All we’d see is human microbes and refuse.
Q. ON THE OTHER HAND, STEPHEN HAWKING THINKS EXPOSURE TO EXTRATERRESTRIAL LIFE COULD PROVE HAZARDOUS TO EARTHLINGS. “IF ALIENS VISIT US, THE OUTCOME WOULD BE MUCH AS WHEN COLUMBUS LANDED IN AMERICA, WHICH DIDN’T TURN OUT WELL FOR THE NATIVE AMERICANS,” DR. HAWKING RECENTLY WARNED. IS HE ONTO SOMETHING?
A. Dr. Hawking suggests an intriguing possibility, although there are alternative scenarios. Aliens might bring some exotic organisms with them to Earth, but would they survive in our oxygen-rich environment long enough to do any damage to humans or the ecosystem? Meteorites from Mars have landed on Earth throughout history, and if any Martian organisms were hitchhiking on these, they have not killed us yet.
Q. THREE YEARS AGO, YOU REDID THE SPARK DISCHARGE EXPERIMENT. WHY?
A. Actually, we didn’t redo it — we reanalyzed it. When, in 1999, Stanley had a stroke, he donated everything in his office to my laboratory. Eight years later, I was giving a talk in Texas and someone there told me that he’d once seen the extracts of the 1953 experiment in a cardboard box in Stanley’s laboratory. Stanley had kept them for all those decades! Though we were very close, he’d never told me about it. I suppose it was just old business to him. But when I got back to San Diego, I asked my staff, “When we moved everything from Stanley’s office, did we get a little cardboard box?” And someone said, “Yeah, its right over there.”
And there it was! Inside, were all these tiny glass vials carefully labeled, with page numbers referring Stanley’s laboratory notes. I was dumbstruck. We were looking at history. It immediately hit me that when Stanley had first done the experiment, analytic tools were still very, very primitive. We have instruments today that are a billion times better. So we then reanalyzed the original materials with the modern tools. And lo and behold, we found that the spark discharge experiment had actually made about 30 compounds. Stanley had shown they’d made only five!
Q. DID YOUR ANALYSIS CONFIRM THE VALIDITY OF THE EXPERIMENT? THERE ARE SOME PEOPLE WHO STILL DOUBT IT.
A. Oh, yes. And more! It showed how easy it was to make a huge number of compounds. What was really interesting was the Murchison meteorite, which fell to earth in 1969, was originally thought to contain maybe 75 amino acids. Three years ago, when we compared the distribution of amino acids in the discharge experiment, they were uncannily similar to those in the meteorite.
I would have loved to have told Stanley about this. But sadly, he was completely incapacitated by the time we found the samples. He died shortly thereafter. I would have loved to have said to him, “Look Stanley, your experiment duplicated what happened on Murchison and you didn’t know it.”
Q. DO YOU THINK IT WOULD BE VALUABLE FOR OTHER SCIENTISTS TO REVISIT OLDER EXPERIMENTS?
A. Listen, I was very fortunate to have had a mentor who had the foresight to preserve his experimental materials. Nonetheless, he couldn’t anticipate all the changes that came with modern analytical chemistry. Today, we are seeing an explosion of knowledge due to new techniques. We ought to use them.
There was just an article in the journal PNAS about how new methods further characterized the compounds in Murchison. Up to now, we knew of hundreds in it. Yet, because of new techniques, they’ve found tens of thousands. And that made me think that yes, we ought to redo the spark discharge experiment. I suspect we’d also find tens of thousands of molecules that were in the prebiotic soup. That, hopefully, is the next project we’ll be pursuing.
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