Is there life elsewhere, or is Earth unique in the universe? This is one of humanity’s great unanswered questions.
One way to approach this mystery is to investigate how life began here on Earth. Our research explores the conditions where a mixture of molecules somehow transformed from chemistry into biology.
In a new study published in Scientific Reports, we shed new light on one possible step in this process: how a fragile sugar from outer space may have helped create the conditions for its own survival on Earth, where it eventually became the backbone of one of life’s most important molecules.
Recreating life’s beginnings
Scientists think life arose from a complex mixture of water, minerals and carbon-containing molecules: the proverbial primordial soup. These mixtures may have been in oceans, lakes or hot springs. They would have been shaped by changing temperatures, flowing water, mineral surfaces and evaporation, creating conditions in which increasingly complex chemistry could develop.
Researchers try to recreate these processes in laboratories, often using purified chemicals and carefully controlled mixtures. This situation helps isolate individual reactions and remove variables, but it can leave out important interactions in nature’s “messy” chemistry.
One molecule studied in these experiments is RNA. RNA plays a vital role in storing and using genetic information in modern organisms, and is thought to have been important in the origin and early evolution of life.
However, RNA doesn’t form easily. Its molecular backbone contains a fragile sugar called ribose. When heated, ribose can break down into brown goop, much as table sugar turns into caramel.
One thing that can protect ribose molecules is the element boron. In the form of borate (a molecule containing boron, oxygen, and hydrogen), it binds to ribose and helps prevent it from breaking down.
Experiments investigating this effect often use simple combinations of purified ingredients. We and our colleagues have been trying to make these experiments more realistic, based on what we know about ancient rocks, minerals and fossils.
The Puga hot springs
We also study modern environments we think may resemble the places where life began. One of these is a field of hot springs at Puga in India, high in the Himalayas.
The waters at Puga contain so much boron that borate salt crusts crunch underfoot like snow. Even so, these waters contain only a few percent of the boron concentration used in some laboratory experiments based on purified ingredients.
That’s because minerals containing boron often dissolve poorly in water. Instead, they precipitate to form crystals — like the borate salt crusts at Puga — leaving less boron and other elements in the water for the chemical reactions thought to be involved in the origins of life.
So could high concentrations of dissolved boron really have existed in those ancient environments?
A two-way relationship
In a new study using real minerals, including borate crusts from Puga, we show that ribose itself may help explain how high concentrations of boron could have existed in fluids on Earth before life began.
We found that ribose helps borate minerals dissolve and inhibits the formation of solid grains. This means more boron stays dissolved in the water and available for chemical reactions.
This new research suggests a two-way relationship. Borate protects ribose from breakdown, while ribose helps keep borate dissolved and available.
The world before life
Four billion years ago, when life is thought to have first formed, Earth would have looked very different from today. There would have been little oxygen in the atmosphere and far more active volcanism, creating sparse volcanic landscapes and green, iron-rich oceans.
A heavy rain of meteorites from the young Solar System would have bombarded the land. These meteorites would have delivered molecules to Earth from space, including water and carbon compounds.
Researchers estimate around a million tonnes of carbon could have arrived each year during this early bombardment. The Murchison meteorite, which fell in Victoria in 1969, hints at what it may have looked like.
Locals collecting fragments reported a strong kerosene-like smell from carbon-containing compounds within the meteorite. Scientists have since identified ribose among its contents, alongside other sugars.
In the absence of microbes, carbon-containing molecules could accumulate wherever supply outpaced chemical breakdown. For example, evaporation in shallow lakes and pools could concentrate organic molecules from space into rich chemical soups.
Primordial soup, on the rocks
Much origin-of-life research examines how minerals helped the chemistry of these soups become more complex. Our study highlights how the soup in turn affected the minerals of early Earth.
Some boron that would otherwise have formed mineral crusts and been buried could instead have remained dissolved in primordial lakes and other waters. This could have changed the types of minerals formed at Earth’s surface.
Ribose itself was probably relatively rare. But other molecules, including ethylene glycol and glycerol, also bind borate.
Their effects on natural mineral deposits need testing, while known interactions between sugars and other minerals suggest broader possibilities. More abundant elements in Earth’s rocks, including silica and calcium, also interact with carbon molecules. This suggests carbon-containing primordial soups could have influenced how other minerals and rocks formed.
Today, organisms shape geology by building shells and coral skeletons through biomineralization. We propose non-living carbon molecules may have begun influencing mineral formation even before life existed on Earth.
Whether these interactions reshaped entire landscapes remains an open question. But exploring them can help scientists test their assumptions about an alien world in our own distant past, improve experiments investigating our origins, and better understand where life might emerge elsewhere.
Luke Steller, Associate Researcher, Australian Centre for Astrobiology, UNSW; Albert Fahrenbach, Associate Professor, School of Chemistry, UNSW, and Martin Van Kranendonk, Professor and Director of the Australian Centre for Astrobiology, UNSW
This article is republished from The Conversation under a Creative Commons license. Read the original article.
Follow us on X, Facebook, or Pinterest
