Are Homo sapiens a one-off, genetic accident? Scientists have identified a group of planets outside our solar system where the same chemical conditions that may have led to life on Earth exist in what they call the Abiogenesis Zone. It’s also possible that if there is extraterrestrial life, that it has, or will, develop in a totally different way than it did on Earth.
“I’m not sure how contingent life is, but given that we only have one example so far, it makes sense to look for places that are most like us,” said Cambridge University astrochemist, Paul Rimmer. “There’s an important distinction between what is necessary and what is sufficient. The building blocks are necessary, but they may not be sufficient, it’s possible you could mix them for billions of years and nothing happens. But you want to at least look at the places where the necessary things exist.”
In 2018, researchers from the University of Cambridge and the Medical Research Council Laboratory of Molecular Biology (MRC LMB), in their Arxiv post, Terrestrial Planets Across Space and Time, found that the chances for life to develop on the surface of a rocky planet like Earth are connected to the type and strength of light given off by its host star.
According to recent estimates, there are as many as 700 million trillion terrestrial planets in the observable universe.
“Getting some idea of what fraction have been, or might be, primed for life fascinates me,” said the head of the Laboratory of Molecular Biology and leading expert on the origins of life, John Sutherland. “Of course, being primed for life is not everything and we still don’t know how likely the origin of life is, even given favorable circumstances – if it’s really unlikely then we might be alone, but if not, we may have company.”
On May 25th, The Galaxy published a post on Technological Intelligence asking: “For what purpose did the human brain evolve?” It is a question that has puzzled scientists for decades, and was answered in 2010 by Colin Blakemore, an Oxford University neurobiologist who argued that a mutation in the brain of a single human being 200,000 years ago turned intellectually able primates into a super-intelligent species that would conquer the world. Homo sapiens appears to be genetic accident. Or are we?
We are the only species of the billions of species that have existed on Earth that has shown an aptitude for radios and even we failed to build one during the first 99% of our 7 million year history, according to Australia National University’s Charles Lineweaver.
We live in a universe where matter is distributed in a hundred billion galaxies, each containing a hundred billion stars, made up of quantum fields where space and time are not existent, that manifest themselves in the form of particles, such as electrons and photons, or as waves. Tucked into the 14-billion-year history of this vast observable universe with 100 trillion planets is a pale blue dot teeming with life and a technological civilization created by a strange species known as homo sapiens.
Rimmer speculates that life may have come from non-life as one big accident. This seems highly unlikely, at least given the way our universe is set up, so if it’s that way, then we are probably the only intelligent life in the universe, maybe the only life at all.
Or maybe the origin of life was directed, in which case it has happened as few or many times as the director deigns, but at least once, at least here.
Or maybe the origin of life occurs due to necessary physical principles acting on conditions that are, in certain regions of our universe, inevitable. Put some likely simple chemicals and rocks near enough to a star and pop! Life. Every time. In this case, life is very likely all over the place.
Or maybe life, Rimmer speculates, arises from incremental chances, incremental steps, maybe with some or all of the chance steps the numbers are fixed a bit, the dice are weighted by particular physical laws and conditions. After all, random isn’t truly random. Even a coin flip is absolutely fixed by basic Newtonian physics. There might be a physical selection after these steps, choosing the structures that replicate however inefficiently over those that don’t replicate at all. In this case, life might be unique to the Earth, all over the place, or in very few places, depending on how unique the steps are and what the probabilities of the steps happen to be.
Principles of Life Universal?
Scientists have identified planets outside our solar system where the same chemical conditions exist that may have led to life on Earth. The researchers, from John Sutherland’s group in the LMB’s PNAC Division and the University of Cambridge Cavendish Laboratory, found that the chances for life to develop on the surface of a rocky planet like Earth are connected to the type and strength of light given off by its host star.
The new study proposes that stars which give off sufficient ultraviolet (UV) light could kick-start life on their orbiting planets in the same way it likely developed on Earth, where the UV light powers a series of chemical reactions that produce the building blocks of life. The researchers identified a range of planets where the UV light from their host star is sufficient to allow these chemical reactions to take place, and that lie within the habitable range where liquid water can exist on the planet’s surface.
This new work is the result of an ongoing collaboration between Sutherland’s group and the Cavendish Laboratory, and builds on Sutherland’s earlier work on the chemical origin of life on Earth.
In 2015, Sutherland proposed that cyanide, although a deadly poison, was in fact a key ingredient in the primordial soup from which all life on Earth originated. John’s group recreated the proposed chemical reactions under UV lamps and generated the precursors to lipids, amino acids and nucleotides, all of which are essential components of living cells.
Rimmer, then an astronomy postdoc with a joint affiliation in the Cavendish Laboratory and the LMB, came across Sutherland’s work and realized that measuring the light used during the earlier laboratory experiments could help identify planets where similar chemistry could take place. The two groups performed a series of laboratory experiments to measure how quickly the building blocks of life can be formed from hydrogen cyanide and hydrogen sulphite ions in water when exposed to UV light. They then performed the same experiment in the absence of light, but only an inert compound which could not be used to form the building blocks of life was produced.
Cool stars, on the other hand, do not produce enough light for these building blocks to be formed, except if they have frequent powerful solar flares to jolt the chemistry forward step by step. Planets that receive enough light to activate the chemistry and could have liquid water on their surfaces reside in what the researchers have called the abiogenesis zone.
An artist’s concept of Kepler-452b, a 1.5 Earth size exoplanet shown above discovered within the habitable zone of a Sun-like star. It is the smallest exoplanet known about so far that definitively resides within the abiogenesis zone: the zone where, given the right surface environment, the UV light is sufficient to form life’s building blocks. (NASA Ames/JPL-Caltech/T. Pyle)
Among the known exoplanets that reside in the abiogenesis zone are several planets detected by the Kepler telescope, although these planets are all too far away to probe with current technology. The diagram above shows which of a select group of confirmed exoplanets (and Earth) lie within the abiogenesis zone. By plotting the amount of UV light available to planets in orbit around different stars, the researchers found that stars around the same temperature as our sun emitted enough light for the building blocks of life to have formed on the surfaces of their planets.
Next-generation telescopes, such as NASA’s TESS and James Webb Telescopes, will hopefully be able to identify and potentially characterize many more planets that lie within the abiogenesis zone. It is of course possible that if there is life on other planets, it has or will develop in a totally different way than it did on Earth.
The work was funded by the MRC, the Kavli Foundation and the Simons Foundation.