What is the origin of life ?
Day after day, scientific discoveries accumulate, allowing us to better understand our planet and our universe. The mapping of the human genome, the discovery of the Higgs Boson (the elementary particule that gives mass to objects) or the construction of synthetic bacteria capable of self-replicating are some of the major scientific advances of the 21st century that remind us how fascinating our world is [1]. Despite the increasing number of scientific publications over the years, one essential question remains unanswered: what is the origin of life? Furtheremore, we can ask ourselves where did the first organic bricks that made the incredible biological diversity that we know today come from? Where do our oldest ancestors came from? Everybody has asked themselves these questions at least once in their lives, but no one seems to have a unanimous answer. Through this short post, we want to present you a scientific theory, that can be worthy of science-fiction films, that tries to answer, at least in part, all of these legitimate questions.
Space life coming from meteorites
According to some scientists, the compounds at the very basis of life were not of terrestrial origin but came from the meteorites that once bombarded the Earth [2]. These meteorites and comets would have crashed on our planet 3.9 billion years ago and would have brought with them very interesting organic compounds: nucleic acids and sugars [3]. These two materials constitute our genetic code and the one of all known species – this would mean that, technically, all life on Earth originates from outer space!
It is only in November 2019 that traces of ribose were observed on meteorites found in Africa and Australia [4]. Ribose is the sugar that allows the formation of RNA (the cousin of DNA) and of which the first living organisms were probably composed of (check our post about RNA/DNA !) [5] [6] . Moreover, the bombardment of the planet during the period named “Late Heavy Bombardment” would have generated a large number of diverse chemical reactions that would have been favourable to life on Earth [7] [8]. Thus, these discoveries let us imagine that our great-great-great-…-grandparents were made up partially, or even completely, of compounds coming from a distant part of the universe.
These discoveries not only provide a hypothesis on the formation of life on Earth, but also allow us to imagine how other forms of life could have formed or could form on other planets. Indeed, our planet is probably not the only one to have been bombarded by these large rocks. Therefore, these compounds may also have been found on other planets where the conditions were favorable to the formation of life.
This, of course, is not the only theory to exist. Other hypotheses postulate that life could have originated in deep sea vents or in the Arctic. Miller’s experiment is one of the best known experiments giving evidence of the formation of life directly on Earth: by reconstructing the early conditions of Earth, this experiment shows that the formation of organic compounds essential for life was possible on our blue planet without any meteorite bombardment [9]. But until we find biosignatures (phenome or substance that proves the presence of life), or evidence of life on other planets, we may never know how we appeared on ours.
For more information, check out these resources:
- A good video to understand the Miller-Urey experiment : https://www.youtube.com/watch?v=NNijmxsKGbc
References :
- https://www.genome.gov/human-genome-project
- https://www.nationalgeographic.org/encyclopedia/meteoroid/
- https://www.nasa.gov/press-release/goddard/2019/sugars-in-meteorites
- Furukawa Y., “Extraterrestrial ribose and other sugars in primitive meteorites”, PNAS, 2019.
- Lehman N., “The RNA World : 4,000,000,050 years old”, Life, 2015
- https://www.nytimes.com/2015/05/05/science/making-sense-of-the-chemistry-that-led-to-life-on-earth.html
- https://www.space.com/36661-late-heavy-bombardment.html
- https://earthhow.com/late-heavy-bombardment-stage/
- Miller S., “A production of amino acids under possible primitive earth conditions”, Science, 1953.
