Did Life Begin on Mars?

Steve Benner’s Meet the Neighbors makes some bold and fascinating claims.

S teve Benner is one of the heavyweights of both theoretical and applied biology. A founder of the field of synthetic biology, he was the first person to synthesize a gene and one of the originators of the RNA-world theory of origin of life. He is also a successful biotech entrepreneur — relevant because his wealth has given him the freedom to speak freely, even when his views contradict NASA and other members of the scientific establishment. His terrific new book, Meet the Neighbors: Life on Mars and How to Find It, is an example of his doing just that: Benner pulls no punches in drawing powerful conclusions based on both his own research and an encyclopedic knowledge of the work of the astrobiology community. Assembling impressive evidence, Benner boldly argues that there is almost certainly life on Mars — and that life originated on the Red Planet before it appeared on Earth.

In its statements supporting its various Mars missions, NASA’s public relations department has always claimed that their purpose was to search for life. They’ve said this because they know that the possibility of extraterrestrial life is what the American people — quite rightly — are most interested in when it comes to Mars. Unfortunately, NASA has failed to follow through.

In point of fact, America’s space agency has not flown a life detection instrument to Mars since the Viking mission, which landed on the Red Planet almost exactly a half-century ago on July 20, 1976. Since that time, NASA has flown orbiters, stationary landers, and rovers to Mars. While these missions have obtained some very useful data on the Martian environment, none have attempted to look for life itself.

So, Benner starts with Viking. The Viking mission deployed two identical landers on Mars, at two widely separated low-altitude and mid-latitude locations. Each of the landers carried three life detection experiments. Two of the experiments tested for autotrophic life by examining whether Martian soil contained photosynthetic microbes that might either fix carbon or release oxygen. The third, known as the labeled-release experiment, tested to see if the soil contained microbes that might break down organic materials via processes such as respiration. All three experiments yielded strongly positive results. As the then-director of NASA’s Goddard Institute for Space Studies, Robert Jastrow, said at the time, “Short of seeing something wiggling at the end of a pin, the case for life on Mars is now as complete as the Viking experiments could make it.”

However, the Viking landers also carried a fourth instrument, known as a Gas Chromatograph Mass Spectrometer (GCMS). The GCMS assessed the chemical composition of the soil, and it detected no organic material in Martian dirt. This came as quite a surprise to NASA’s scientists, because even if there was no life on Mars, they expected that some organics would be found — if from no other sources than meteorites, which frequently contain sturdy organic compounds known as polycyclic aromatic hydrocarbons (PAHs) that can survive impact.

But not even these could be detected. Rather than view the GCMS results as suspect, however, the conclusion drawn by Viking science team leader Gerald Soffen was: “That’s the ball game. No organics, no life.” While the labeled-release experiment’s principal investigator, Gil Levin, continued to insist that his device had in fact detected life, the other researchers all went along with the team conclusion and devised non-biological explanations for their results.

It was thus concluded that Viking had not found life on Mars. Over the years this claim not only became gospel, but in textbook versions was exaggerated to say that Viking had definitively shown that there was no life on Mars. Levin (who, interestingly, as the owner of a water quality testing technology company, was financially independent of NASA research grants) never wavered in defending his device’s conclusion that there was life on Mars until his death in 2021. As a result, however, he became regarded as a crank, and even had shrimp thrown at him when he stood up to speak at a conference dinner in his later years.

Benner was not directly involved in Viking, and as an outsider, initially accepted the community conclusion. But around the turn of the century, he began to suspect that something was amiss and decided to revisit the mission’s original data reports.

He quickly discovered a number of problems. First, as Levin continued to point out, the GCMS was not sensitive enough to detect organics in the soil of Chile’s Atacama Desert — a place where microbial life certainly exists, albeit in sparse concentrations. But more importantly, Benner discovered that the GCMS had measured organics. Specifically, when tested in space on the way to Mars, it detected freon gases; once on the surface of Mars, it detected methyl chloride emitted from samples of Martian soil.

Now, freon gases are common refrigerants, and those detected in space were certainly contaminants originating on Earth. But methyl chloride, a simple molecule consisting of one carbon bound to three hydrogens and a chlorine, is a gas even at Mars’s ambient temperatures. Consequently, it couldn’t have been native to Martian soil — it would have instantly evaporated. The team therefore dismissed its presence in Martian soil, as sampled by the GCMS, as experimental error, putting it down as a refrigerant contaminant even though it is not used for any such purpose on Earth. But Benner wasn’t satisfied with that conclusion, and began to wonder: Where could the methyl chloride have come from?

The answer began to become clear in 2007, when the Phoenix lander science team, led by University of Arizona professor Peter Smith, detected perchlorates in Martian soil. These compounds are oxidizers, and while they are not strong enough to oxidize organic materials under normal Martian environmental conditions, Mars soil placed in the GCMS was heated up to high temperatures. In such a furnace, the perchlorates would have rapidly oxidized any Martian organics present in the soil (including even tough PAHs), procuring — among other products — methyl chloride.

With this mystery solved, the Viking GCMS results were completely discredited. The GCMS could not have detected organics because it destroyed them! The truth had become clear: Soffen called the ball game against the life detection experiments based on defective data. Not only that, but in 2020 we learned that organics are in fact present on Mars, when the Curiosity rover detected them in large quantities in Martian mudstones.

That leaves us with all three life detection experiments on both landers reporting positive results, and no grounds for dismissal. The weight of evidence now stands with life.

Levin had been right all along.

But the question of whether there is life on Mars is only the start of Benner’s inquiry. The more important question is how it got there — or to our own planet, for that matter.

There is evidence for the existence of life on Earth going back roughly 4 billion years. The Earth formed 4.5 billion years ago; for its first several hundred million years, it was too hot for liquid water. So, life appeared here practically as soon as it could. This implies one of two things: that the mysterious chemical processes that lead to the development of life are highly probable, or that the seeds of life are floating in space and take root in any world as soon as it offers acceptable conditions. Either theory would imply that life is plentiful in the universe. But which one accounts for our ancestry? Benner opts for both.

In many ways, early Earth and early Mars were twins. Both were rocky planets with oceans of water, volcanic geology, and atmospheres consisting of mixtures of nitrogen and carbon dioxide. But Mars cooled first and thus had liquid water first. The Earth, however, had much more water — so much more that in its youthful days, before geologic actions had lifted up continents, our planet was completely covered by a global ocean. In contrast, being much drier, young Mars had both dry land and water. This relative impoverishment in water was a critical advantage for Mars as a cradle for life, Benner says, because it allowed small amounts of spontaneously created complex chemicals to be concentrated for further reaction in shrinking lakes or ponds. In contrast, Earth’s global ocean would dilute any interesting chemical novelties to insignificance.

Benner describes in some detail the processes necessary for the creation of the chemical precursors for life, notably ribose nucleic acid (RNA), which he has duplicated under simulated early Mars conditions in his lab. To achieve the duplication, water, the right kinds of rocks, atmospheric gases, and sunlight all need to be available simultaneously in the same place. That was true on a wet and rocky Mars, but not on an Earth dominated by oceans.

There is a natural transport of materials between Mars and Earth, caused by the impact of meteors that scatter rocks into space. This is still going on today. It is estimated that about 500 kilograms of Martian rocks land on Earth every year. Scientists have collected dozens of them, and on the basis of their studies it is clear that the processes involved in impact, flight through space, and reentry and landing on Earth would, in many cases, not heat the rocks sufficiently to sterilize them. During the solar system’s early period, the interplanetary rock traffic would have been much heavier. In other words: If life appeared on Mars before it did on Earth, it would have had no difficulty getting here.

In all probability then, according to Benner, life on Earth came from Mars. It’s probably still coming, but late-coming Martian immigrants can’t survive here, because local conditions have changed a lot since Earth’s early days. For one thing, photosynthetic organisms have radically changed the composition of Earth’s atmosphere, turning its CO₂ into oxygen. This has caused the surviving descendants of the Earth’s earliest inhabitants, anerobic bacteria, to migrate deep underground where they can be sheltered from oxygen, which they find toxic.

So, science fiction films about killer plagues from space notwithstanding, we shouldn’t fear finding life on Mars. If the Red Death could come here to infect our planet, it already would have done so — billions of times. Rather, we should seek Martian life to find fundamental truths about the laws of nature.

Scientists have traced back the evolution of life on Earth to anerobic bacteria, but not further. Yet as simple as they are, these microbes are actually incredibly complex organisms that involve all sorts of intricate molecular machinery. They could no more be the first life forms than an iPhone could be the first machine. There had to first be even more elementary life forms. The fact that we found no such free-living, simpler “prebacteria” on our own planet is another reason to suspect that life did not originate here.

But perhaps they can be found on Mars. Indeed, perhaps by going to Mars we can find not just other types of life, but earlier types of life. Certainly, if life has been on Mars for four billion years, it will have had plenty of time to explore evolutionary options in novel directions not taken on Earth. This will tell us quite a bit about the range of possibilities available to life in the universe.

On Earth, we generally find that even as evolution generates new and more complex forms of life, representatives of the simpler forms continue to persist. Can the pre-bacteria, or still simpler forms, be found on Mars today? If so, and if Benner is correct, studying them could tell us quite a bit not only about the origin of life, but indeed about life’s fundamental nature.

Is life on Earth a local oddity, or is it the local representative of a vast and incredibly varied cosmic phenomenon? What’s really going on in this universe of ours, anyway?

Let’s go to Mars and find out.