University of Alberta geochemists have discovered a missing piece to one of the great mysteries of science — the origin of life on Earth.

That fateful spark is believed to have occurred on the ocean’s floor, fuelled by warm, mineral-rich hydrothermal vents. But scientists have long puzzled over how the right fertilizer — particularly the forms of carbon and nitrogen necessary to create and sustain life — could have existed without the benefit of the sun.

After analyzing rock samples from hydrothermal vents drilled over a depth of about 200 metres into the crust in the South China Sea, Long Li and his team in the Department of Earth and Atmospheric Sciences found evidence of a chemical process — called abiotic nitrogen reduction (ANR), a reaction driven by minerals as catalyst — that likely produced the necessary nutrients for life. A key part of those is ammonium, says Li, crucial for the abiotic synthesis of organic compounds to develop the first life.

The results of their discovery — in collaboration with a group at the South China Institute of Oceanography — were published Nov. 28 in Nature Communications.

“This definitely fills in the gap for the first-step reaction in the origin of life,” says Li. “People have searched for this reaction for a long time, but this is the first time we have convincing evidence to show it is occurring on Earth, and probably did occur on early Earth as well.”

Laboratory experiments have demonstrated the ANR reaction before, but finding its telltale signature in the ocean itself proved difficult, say the study’s authors, because of sample contamination by the modern biological nitrogen cycle.

The discovery also helps to shed light on a long-standing scientific problem known as the “faint young sun paradox,” which considers how liquid water, also essential for life, could have existed on the early Earth when the sun’s rays were weaker and, according to climate modelling, Earth’s surface temperature should have been well below 0 C.

And yet there is convincing geological evidence that the planet was indeed warm enough for liquid water at least 4.4 billion years ago, says Li, likely due to greenhouse gases such as carbon dioxide, methane and ammonia in the atmosphere. Submarine hydrothermal vents could manufacture these greenhouse gases, he notes.

The evidence of ANR in the South China Sea is sufficiently compelling to assume it occurred elsewhere in the ocean, he adds.

“We definitely need more evidence to show that. But since the conditions for ANR are common in both modern and ancient oceans, we reasonably speculate that this could happen globally over Earth’s history.”