Could scientists have been wrong about how life began on Earth?

Dubai: For more than a century, scientists have explored the possibility that life on Earth began with chemical ingredients delivered by comets from outer space. But a new study suggests those icy visitors may have been travelling too fast to deliver their precious cargo intact, challenging a long-standing theory about how life began.

The research, published in the journal Scientific Reports, found that comets striking the early Earth would generally have generated such extreme temperatures and pressures that delicate organic molecules essential to the emergence of life could not survive.

The findings raise a fascinating question: If comets did not deliver the building blocks of life, where did they come from?

A theory dating back more than a century

Scientists have long considered comets possible carriers of water and organic compounds to the young Earth.

Often described as “dirty snowballs”, comets contain ice, dust and organic material, making them potential vehicles for transporting the chemical ingredients needed for life.

The broader idea that life’s ingredients came from space dates back more than a century, while theories specifically linking comets to life’s origins gained prominence during the 20th century.

According to CNN, the new research challenges the assumption that comet impacts could have deposited sufficient quantities of intact organic molecules on Earth’s surface.

Researchers estimate that more than 100,000 comets measuring over 100 metres across may have struck Earth during its early history, more than four billion years ago.

But the enormous speed of those collisions appears to have worked against the survival of their chemical cargo.

What the simulations revealed

Led by Richard Anslow, who conducted the research at the University of Cambridge’s Institute of Astronomy, scientists used computer simulations to examine the conditions under which comets could have delivered hydrogen cyanide, or HCN, to early Earth.

Despite its toxic reputation, hydrogen cyanide is an important precursor in prebiotic chemistry, the chemical processes that can produce the building blocks of life.

The compound contains hydrogen, carbon and nitrogen and can participate in reactions that produce more complex organic molecules.

However, the simulations suggested that successful delivery would have required an exceptionally favourable combination of impact speed, angle and environmental conditions.

“It’s kind of a romantic idea, but our results suggest it’s highly unlikely,” Anslow told GB News.

According to CNN, 54 per cent of the simulations produced no successful delivery events, while only a small minority produced as many as three.

Even those rare events would not necessarily have created conditions suitable for life.

The numbers make the challenge even greater

GB News reported that the researchers calculated that even if cometary material had been deposited into Earth’s oceans simultaneously, the resulting hydrogen cyanide concentration would have reached only about 0.75 micromoles per litre.

That is approximately 13,000 times below the concentration considered necessary for the chemical reactions examined in the study.

The researchers also estimated that comets delivered about 2.63 quadrillion tonnes of material over 500 million years, equivalent to approximately 0.19 per cent of the mass of Earth’s oceans.

Even if hydrogen cyanide survived an impact, it could have dispersed rapidly in water, making it difficult for the chemical reactions associated with life’s origins to proceed.

Could asteroids hold the answer?

The findings do not mean that life’s ingredients could not have come from space.

Asteroids remain another possibility because they generally strike Earth at lower speeds than comets.

Recent studies of samples collected from the asteroids Bennu and Ryugu have revealed a rich assortment of organic molecules, including amino acids associated with proteins.

Another possibility is that the necessary compounds formed naturally on the early Earth through reactions involving its atmosphere, water and minerals.

Scientists have not established which pathway, or combination of pathways, ultimately led to the emergence of life.

Why Mars enters the picture

Perhaps the most intriguing implication concerns Mars.

The researchers suggest that the Red Planet may have offered more favourable conditions for comet-borne molecules to survive impacts billions of years ago.

Because Mars is smaller than Earth and farther from the Sun, comets typically strike it at lower speeds, potentially allowing more organic material to survive.

That does not mean life began on Mars, but it raises fresh questions about whether the planet once possessed the chemical conditions necessary for life.

The findings could also help scientists identify promising planets beyond our Solar System when searching for environments capable of supporting prebiotic chemistry.

Is the comet theory finished?

Not necessarily.

Queenie Chan, an associate professor of Earth sciences at Royal Holloway, University of London, told CNN that hydrogen cyanide might have reacted to form other biologically important compounds before comets entered Earth’s atmosphere.

Such compounds could have been more likely to survive an impact.

Other researchers also caution against eliminating comets entirely from the story of life’s origins.

The new study therefore challenges one proposed route by which comets could have supplied the ingredients for life, rather than disproving every possible contribution from space.

For now, the greatest mystery remains unanswered: How did a collection of simple chemicals on the young Earth eventually give rise to the first living organisms?