How life first began remains a mystery. How did lifeless molecules become cells with membranes, genetic material, and the ability to obtain energy?
Micrometeorites are dust from space that continuously rain down on Earth. Some carry substances essential to life, including water, amino acids, fatty substances, and sugars.
Could the precursors of cells have first emerged on surfaces like these?
Irep Gözen and her colleagues have now shown that tiny, cell-like fatty capsules and tubes can form spontaneously on micrometeorites.
"We observed primitive, cell-like structures that organised themselves on the surface of micrometeorites. They are surrounded by a lipid membrane, like modern cells," Irep Gözen tells Science Norway.
Annonse
Some of the capsules are connected by very thin, nanoscale tunnels. Primitive cells may have used such tubes to exchange material with one another, including fragments of genetic material, Gözen explains.
Norwegian micrometeorites
"This isa milestone. It could provide a plausible explanation for how the cell membrane came into being," says Jon Larsen, who took part in the study.
He has developed a method for finding micrometeorites on rooftops in urban areas that is now used internationally. The jazz musician is a guest researcher at the University of Oslo.
Irep Gözen contacted Larsen to gain access to micrometeorites for her research.
"She had already been working with other, similar surfaces for many years. We met while keeping two metres apart during the pandemic and decided that I would find three different micrometeorites," Larsen says.
Irep Gözen contacted Jon Larsen to use micrometeorites in her research. They have since met again.(Photo: Jon Larsen)
Do things by themselves
Irep Gözen has studied how fatty substances, also known as lipids, behave on different surfaces and how they can do things by themselves without genetics or proteins.
She works at GOMOD AB, a research and consulting company, and was previously a researcher at the University of Oslo.
"I have spent many years developing and testing the hypothesis that solid surfaces played a crucial role in the emergence of primitive cells because of their interfacial energy – the energy that arises at the boundary between a solid material and its surroundings," says Gözen.
"Primitive cells were probably soft structures without mechanisms that could shape and reshape them. But when soft material comes into contact with solid surfaces, it can self-organise into highly unusual shapes," she explains.
Here we can see tiny fat capsules that formed spontaneously on the surface of a micrometeorite.(Photo: Irep Gözen)
Behaved somewhat differently
In the new study, Gözen and her colleagues tested three types of lipids found in archaea, bacteria, and plants.
Annonse
They used grains of sand from Swedish beaches as control materials.
One finding was that lipids from archaea formed large numbers of tiny capsules on micrometeorites, but very few on the grains of sand.
The opposite was true for the bacterial lipid, while the plant lipids formed the densest structures on the micrometeorites.
Gözen calls them protocells, a possible precursor to the first cells.
"Several thousand tonnes of micrometeorites fall to Earth every year, and this has been happening since the planet was formed. Research shows that they also contain organic material. They function almost like mini-laboratories from space, carrying molecules that are important for life," the researcher explains.
She also points out that they can easily be transported by wind and ocean currents, allowing them to reach environments where conditions may have been suitable for life to emerge.
"Our results strengthen the theory that micrometeorites may have played an important role in the origin of life, thanks to their unique properties," says Gözen.
“Micrometeorites are unlike anything else,” says Jon Larsen.(Photo: Jan Braly Kihle / Jon Larsen)
In the past, you had to go to the South Pole
In the past, you had to travel to the South Pole to find micrometeorites, according to Jon Larsen.
He discovered a way to find micrometeorites on rooftops.
It all began in 2009, when Larsen became curious after noticing a black speck on the white breakfast table on his veranda. He wondered whether it might be a tiny rock that had fallen from the sky.
He began systematically searching for micrometeorites and contacted researchers in the field.
"Everyone said, ‘Just forget it, Jon, it’s impossible to find them'," the researcher recalls.
Larsen nevertheless continued searching in road dust, gutters, and all kinds of other places.
"I classified and mapped all kinds of dust I could find across 50 different countries. Through a process of elimination, I managed to find the first micrometeorite after seven years. It looked completely different from what people had been expected, and that's why they had not been discovered before," he says.
The micrometeorites from the South Pole were old and had eroded surfaces.
"This has now been mapped in detail, and basically anyone can find what I would call the most exotic particles in the universe," he says.
Unlike anything else
"Micrometeorites are unlike anything else, because they have been through something no other rock has been through," Larsen says. "They have come hurtling towards Earth at hypervelocity, 50 times the speed of a rifle bullet."
They melt, solidify again, and recrystallise.
"You can see traces of this; they are aerodynamic," Larsen says.
Some micrometeorites enter the atmosphere at such a shallow angle that they reach the ground without melting. This applies to around five per cent of micrometeorites.
"They contain an entire toolbox of exotic organic molecules, meaning carbon compounds – everything from amino acids to phospholipids," says Larsen.
In those that have melted, the organic molecules have been boiled away, but around five tonnes of unmelted micrometeorites fall to Earth every day, according to Larsen.
Early in Earth's history, the amount of cosmic dust falling to the planet was 100 times, or perhaps even 1,000 times, greater than it is today, he says.
In the new study, the researchers tested micrometeorites that had melted to varying degrees, but none that were completely unmelted. The completely unmelted ones are porous and are destroyed by water. To find them, you have to search in the ice layers of Antarctica, Larsen says.
Close-up showing the surface texture of a micrometeorite.(Photo: Irep Gözen)
Exciting findings
Dag O. Hessen is a biologist and professor at the University of Oslo. Although he was not involved in the new study, he describes the findings as exciting.
"The study brings together an area Irep Gözen has been working on for a long time with Jon Larsen’s research into particles that rain down on Earth from space," he says.
Dag O. Hessen is a biologist and professor at the University of Oslo.(Photo: University of Oslo)
"Under certain conditions, fatty substances in water will spontaneously form a hollow sphere. Gözen has shown that when these fatty spheres rest on a mineral surface, they can spontaneously divide when water is added. The resulting ‘daughter spheres’ remain connected by tube-like structures made from the same lipids," Hessen explains.
Cellular material, such as DNA, can be exchanged through these structures. According to Hessen, this is somewhat similar to the system bacteria use to exchange genetic information.
"The mineral surface could consist of clay particles – or micrometeorites," he says.
They are not claiming that this is how life began
One of the theories about the origin of life is that important ingredients may have been brought to Earth from space, says Hessen.
"We know that complex macromolecules can reach Earth in this way, perhaps also fatty substances that form membranes," he says.
One of the challenges in explaining the origin of life is the ‘problem of simultaneity,’ according to Hessen. Both an information system – that is, DNA or RNA – and a reading system capable of translating DNA or RNA into proteins are needed, and all of this must be enclosed within a membrane to form a cell.
"This article does not claim that this is how life originated on Earth. We may never know exactly where and how it happened. But it points to the possibility that key building blocks, such as membrane lipids, may have ‘rained’ down with micrometeorites," he explains.
Because micrometeorites also reach other planets, the same process could have occurred elsewhere, Hessen says.
Life on other planets?
Larsen says the same.
"We know that cosmic dust is everywhere.That means that if we discover that micrometeorites played a role in the emergence of life on Earth, the likelihood that the same thing happened elsewhere in the cosmos suddenly increases considerably," he says.
Irep Gözen wants to continue researching the field.
"The initial method has now been established, and the results are very exciting," she says.
The next step will be to investigate how lipids behave on meteorites representing a broader range of types, she says.
