Olivine can form as a gemstone, peridot, but it’s anything but preciously rare. On Earth, it’s the most abundant mineral in the upper mantle and a main component of the basalt rocks that form oceanic crust. Beyond Earth, scientists have found olivine everywhere from Mars, where it’s been spotted by rovers, to asteroids. It’s even present in cosmic dust.
Now, new research published in Earth and Planetary Science Letters has suggested that this cosmically cosmopolitan mineral can help turn formaldehyde, a toxic gas, into sugars. The finding could help explain how the earliest organisms obtained sugars, which they use for energy and to build genetic molecules such as RNA and DNA.
The first cell couldn’t have produced its own building blocks. They must have formed through reactions that don’t involve life.
Today, life creates its own amino acids, fats, sugars, and nucleic acids—critical components that create and sustain many biologic processes. But the first cell couldn’t have produced its own building blocks. They must have formed through reactions that don’t involve life.
Scientists have long thought that the formose reaction, which takes in formaldehyde and spits out a mix of different sugars, may have played a role in creating at least one component of the building blocks of life. Formaldehyde is a simple molecule consisting of a carbon atom bonded to two hydrogen atoms and one oxygen atom. Though rare on Earth’s surface today, it is common in the universe and has been identified in asteroids, in comets, and even in the interstellar medium. It’s possible that impacts delivered formaldehyde to early Earth.
Before Life
The formose reaction begins with the formation of a molecule called glycolaldehyde from two formaldehyde molecules. Glycolaldehyde is the simplest molecule that follows the general chemical formula for sugars.
That first step is the hardest, said study author and astrochemist Vassilissa Vinogradoff of Aix-Marseille University in France. Without a catalyst, it is slow to produce glycolaldehyde, and this holds up the rest of the formose reaction. So it needs a boost, especially when the reaction takes place in water.
Once glycolaldehyde forms, Vinogradoff said, the formose reaction becomes self-sustaining. It consumes formaldehyde to regenerate glycolaldehyde and churn out more and more monosaccharides, or simple sugars. (The name itself is a portmanteau of formaldehyde and aldose, one category of monosaccharide produced by the reaction.)
Given enough time, this cyclical reaction could produce “kilograms, tons, maybe megatons of sugars,” said organic chemist Oliver Trapp of Ludwig Maximilian University in Munich, Germany, who was not involved in the study. Showing how this reaction could get started under natural conditions, he said, is a “remarkable step.”
Vinogradoff and her colleagues wondered whether olivine-rich rocks, which would have been abundant on early Earth and elsewhere in the young solar system, might have been the catalyst for the planet’s first formose reactions.
“This reaction forms many, many, many compounds, and analysis is very, very difficult.”
The researchers reacted formaldehyde with finely ground olivine-rich rock that they carefully cleaned to avoid contamination with organic molecules. (They also set aside some formaldehyde and olivine separately as controls.) The reaction chambers were filled with water and kept warm and oxygen-free. Such conditions are not unlike those that scientists expect existed at hydrothermal vents on early Earth or within watery asteroids. After 2, 7, and 45 days, the team took samples and measured the reaction products using a technique called multidimensional gas chromatography.
“This reaction forms many, many, many compounds, and analysis is very, very difficult,” said prebiotic chemist Yoshihiro Furukawa of Tohoku University in Japan, who was not involved in the study. “The authors used a state-of-the-art analysis.”
The experiments revealed that in the presence of olivine, glycolaldehyde—and sugars—formed much more efficiently. Olivine also helped the reaction produce more complicated sugars such as glucose. Chemical models suggest that the surface of olivine interacts with formaldehyde molecules in a way that makes it easier for their carbon molecules to form bonds to each other.
Because olivine is widespread, the right conditions for making sugars from formaldehyde could have occurred—and could still occur—throughout the solar system, from the seafloor of early Earth to the interiors of asteroids.
Olivine’s ubiquity makes the finding relevant to not just one hypothesis for the origin of life, but several. The mineral is already central to a hypothesis placing the origin of life at hydrothermal vents in Earth’s primordial ocean. The warm, alkaline fluids at these vents come from a reaction between olivine and seawater.
Other hypotheses involve the delivery of organic molecules from space. Furukawa and his colleagues recently identified sugars, including ribose, a key component of genetic molecules, in meteorites. Because certain asteroids contain olivine and formaldehyde, the new results could help explain the existence of such space sugars.
“Olivine is a common mineral,” Vinogradoff said. “That’s the interesting point.” That it could catalyze such a potentially important reaction is something “we had not imagined before.”
—Elise Cutts (@elisecutts), Science Writer