Geochemist Benjamin Tutolo argues in a new peer-reviewed journal paper that hydrothermal vents are an unlikely birthplace for Earth’s life. The origin-of-life theory relies on outdated ocean chemistry assumptions and incorrect mineral and acidity levels present during our planet’s earliest days.
If you ask a scientist how life appeared on Earth, the story usually points to one of two places: a warm, mineral-rich pool on the surface, or a deep-sea vent pumping hydrogen-rich fluid through the ocean floor. Both tales are highly engaging, but according to a provocative new perspective by University of Calgary geochemist Benjamin Tutolo, only one holds any water.
Challenging a Deeply Ingrained Scientific Hypothesis
Tutolo laid out his perspective in the peer-reviewed journal PNAS. He noted that deep-sea vent hypotheses are embedded deeply in our culture to the point that many of us no longer question them.
Hydrothermal vent hypotheses for the origin of life are ingrained in our culture to the point that many of us no longer question them,
Tutolo told ScienceAlert.
Benjamin Tutolo, geochemist at the University of Calgary, via Sciencealert
Leading Theory For How Life on Earth Began Is
Tutolo added that he even has a children’s book that he used to read to his kids that points to hydrothermal vents as the location where life originated. Based on the evidence at hand, however, he considers the scenario highly unlikely. That would require the systems to work in ways that we know that they do not, and that is obviously a fundamental issue,
he said.
Outdated Chemistry and the Lost City Discovery
Just this year, a review concluded that deep-sea hydrothermal vents and their potential role in the origin of life remain a consistent hypothesis in the race to understand how living cells arose from the extreme conditions of our young planet.
Tutolo agrees that the hypothesis has remained consistent through the years. But he argues it is now inconsistent with current evidence. Today, we know that these deep-sea vents are not as alkaline as we once thought, nor as sulfur-rich. We also know more about what Earth’s oceans looked like almost four billion years ago, when life first appeared.
Outdated assumptions about the chemistry of the ancient oceans seem to have played a role,
he explained to ScienceAlert. For example, many vent hypotheses focus on sulfide minerals as facilitators of primordial metabolisms, but alkaline vent fluids, the rocks that host them, and the ancient oceans would have all been essentially barren of sulfur.
The alkaline-vent origin-of-life hypothesis took off. But it left reality in the dust, according to Tutolo. When humans got their first glimpse of hydrothermal vents on the deep ocean floor in the 1970s, they were shocked to find the dark and inhospitable habitats thriving with life. Over the next few decades, scientists hypothesized that perhaps extreme environments like these once breathed life onto our planet. Then, in the year 2000, researchers found the Lost City Hydrothermal Field near the Mid-Atlantic Ridge. The location’s tall carbonate chimneys seemed to host a relatively warm, alkaline, and hydrogen-rich environment. That was just the sort of habitat that some scientists thought would have hosted Earth’s first life.
Flaws in the Natural Battery Concept
The Weirdest Theory Yet for Why Life on Earth
A central pillar of the alkaline-vent hypothesis involves proton gradients. The difference in acidity between the early ocean and the alkaline vents is thought to have provided a natural chemical battery, powering reactions that could have eventually produced life. However, highly alkaline measurements were observed when vent fluids were brought to the surface and cooled. Under the temperatures and pressures found at hydrothermal vents, the fluids are considerably less alkaline.
These problems are so fundamental that hydrothermal vent hypotheses for the origin of life need to be taken back to the drawing board,
Tutolo said. They all rely on a similar series of assumptions, and this work demonstrates that these assumptions are misguided.
Benjamin Tutolo, geochemist at the University of Calgary, via Sciencealert
Furthermore, many vent hypotheses rely on sulfide minerals as facilitators of primordial metabolisms, but alkaline vent fluids, the rocks that host them, and the ancient oceans would have all been essentially barren of sulfur.
What Comes Next for Origin-of-Life Research
As geoscientists reevaluate long-held assumptions about primordial ocean chemistry, the debate exposes how human wishful thinking and early excitement over extreme ocean habitats shaped decades of research.
