Study casts doubt on comets as source of Earth’s life-building chemicals

On November 2, 2026, University of Cambridge researchers challenged the idea that comets supplied early Earth with the chemicals needed for life to begin. Their study, published in Scientific Reports, examined whether hydrogen cyanide carried by comets could have reached the planet’s surface in sufficient quantities to support the chemical reactions associated with life’s origins.

The researchers used computer models to assess comet impacts and the evolution of comets. They concluded that comets usually approach Earth at such high speeds and steep angles that most of the molecules would be destroyed. Comets under 100 metres wide could break apart in high-altitude airbursts, while even kilometre-sized objects would fragment, the study said.

The amount of hydrogen cyanide that might survive and dissolve in Earth’s water would be far below the level needed to start the relevant reactions, the researchers found. Lead author Richard Anslow said the comet explanation was appealing but appeared highly unlikely. He said a successful delivery would require a rare combination of impact conditions and subsequent chemical processes.

The study points to other possible sources, including carbon-rich asteroids and chemicals formed on the young Earth. Hydrothermal vents are another proposed setting for the creation of life’s basic ingredients.

Comets may have had better odds of delivering molecules to Mars, whose smaller size and thinner atmosphere could allow more material to reach the surface. The researchers stressed that this does not establish that such delivery happened there. Their findings may help guide searches for planets where comet impacts could leave chemicals intact.