Protocells from Meteorite Dust

Contemplating life's own extraterrestrial origins

Among the theories surrounding the origins of life on Earth, the concept of panspermia is definitely the one that most closely approximates science fiction. Panspermia posits that the “seeds” of life travel freely through interstellar space, hitchhiking on asteroids, comets, and space dust. Upon reaching the shores of a habitable planet, these “seeds” then “blossom” into different forms of biological life. While the theory of panspermia doesn’t really resolve the question of our origins (instead, it indefinitely defers it), part of the allure of the theory lies in its ability to blur the line between the terrestrial and the extraterrestrial, triggering the unfamiliar experience of looking at ourselves as aliens.

The blurry photograph above captures microscopic vesicles obtained from organic compounds directly extracted from meteorite dust. They were first discovered and studied in 1985 by David Deamer, a biologist renowned for his research on the origin of life. Deamer found that fatty compounds extracted from the space rock could easily self-organize into small, double-layer lipid membranes when dissolved in water. These lipid membranes bear a striking resemblance to the membranes present in living cells today.

As Deamer reported in a 2019 interview for the journal Life,

“I put a drop of the extract on a microscope slide, added water, and settled down to watch what happened. It was amazing! I could see the water penetrate into the dried extract, causing round structures to form. A few minutes later I watched thin membranous vesicles begin to ooze away from the surface. I quickly snapped some photographs and made prints. A few of my colleagues in the Zoology department were having lunch down that hall and I barged in to show them my discovery. Alas, they expressed polite interest, then returned to their lunches.”

The compounds extracted from the meteorite in question come from the renowned Murchison meteorite, which made impact in Australia back in 1962. Soon after its arrival, it quickly attracted scientific attention because of its remarkably high concentration of organic compounds. These included more than 100 different amino acids, some of which are essential to biological life. The discovery revolutionized our understanding of astrochemistry, showing that biological molecules are much more common in the universe than we previously thought. This, of course, had profound implications for both the quest for extraterrestrial life and the study of the origins of life on Earth.

The Murchison meteorite is classified as a “chondrite” - a type of rock originating in the early solar nebula, long before the formation of planets. Because of their ancient origin dating back to about 4.5 billion years, chondrites offer a unique “snapshot” of the composition of the ancient Earth. Studying the composition of these rocks is like looking into a time machine, giving us access to the geochemistry of our planet in a way no other geological specimen can provide.

The discovery of the “proto-biotic” vesicles extracted from the Murchison meteorite points to a possible origin of life scenario known as the “Lipid World”. The theory was originally proposed in the early 20th Century by Russian chemist Aleksandr Ivanovič Oparin. According to this theory, the formation of a closed, semi-permeable membrane marked the first step in the birth of the first “protocells” - the most rudimentary life forms on Earth. Unlike other origin of life theories, such as the “RNA World” scenario (which probably deserves its own separate discussion), the Lipid World theory emphasizes the significance of self-organization and molecular cooperation over self-replication and competition in the emergence of complex organisms.

Although we may never know whether extraterrestrial meteorites ever played a role in our ancient origins, looking at these alien lifelike structures, which traveled for billions of years before finding their place on our planet, evokes a feeling of both proximity and estrangement. I think about the inconceivable depth of time that separates me from them, but I am simultaneously reminded of the antiquity encoded within my own molecular memory. As I contemplate them as aliens, I am also confronted with my own material weirdness. Every origin myth carries a delicate balance between universal familiarity and radical outsideness. I feel that there is something valuable in both of these experiences - and that maybe they are not so different after all.

References

Deamer, D. Boundary structures are formed by organic components of the Murchison carbonaceous chondrite. Nature 1985, 317, 792–794.

Damer, B. David Deamer: Five Decades of Research on the Question of How Life Can Begin. Life 2019, 9(2), 36.