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Our origins represented in religion proved a useful tool for the emerging science of the Enlightenment with the image of a tree, sometimes with roots, and other times, a trunk and numerous branches. This became the linear model for the theory of how life came to be on Earth, starting with the first cell and branching out into the representational tree. The assumption is a single seed, cell, and point of origin.
Why do we look at origins when it comes to life in such a linear way?
A recently published article in Scientific American asks the question “How did life begin?” It describes the research of a team led by evolutionary biologist Bill Martin, from Heinrich Heine University Düsseldorf in Germany. They argue that evidence shows that life began twice on Earth.
The question of where life began is discussed in the article, pointing to hydrothermal vents as the most likely source of “genesis,” the name that inspired the field of genetics and derived from the Greek γένεσις, meaning “origin.”
Hydrothermal vents, Martin argues, are likely where our universal common ancestor emerged. Called the ur-organism, it was a bacterium-like cell from which all life on Earth descends. Was it alive? Not necessarily. It may have been more like a self-contained, membrane-sheathed droplet filled with chemical ingredients that were the precursors of life, including some form of genetic encoding.
The article talks about a half-alive ancestor that responded to the energy and mineral output of the hydrothermal vent environment that introduced prebiotic elements, the second origin factor, to the mix. The ur-organism’s absorption of the prebiotic element, when combined with its encoding capability, allowed, during replication, the passing along of genetic traits to create the first functioning cell. Martin calls it “one origin of the genetic code but two origins of life.”
As interesting as the Martin team hypothesis is, others point to a multiple origins hypothesis.
Why would life emerge from a “singularity” when so much of what we observe on Earth today doesn’t reflect single origins?
For example, look at the emergence of human language. Today, humans communicate using over 7,000 spoken languages. Of these, a little more than half are written. Characterizing language has produced incredible discontinuities. Look at Egyptian hieroglyphics versus Greek. They bear no resemblance to each other even though their origins are in reasonable geographic proximity. When hieroglyphics became lost to history, it took a Rosetta Stone for us to decipher the former because of the accompanying Greek translation.
At a restaurant a few days ago, one wall was covered in Thai script. When I did some research, I found that the Thai written language originates from South India. Like hieroglyphics, it bears no resemblance to the written languages to which we are more familiar. The same can be said about Chinese, 3,300 years ago, or Mesoamerican scripts from Central Mexico and the Yucatán, 2,700 years ago.
What supports a single origin and the subsequent tree is the one thing we find common to all living things here on Earth: DNA (deoxyribonucleic acid).
Most scientists see DNA’s emergence as the genesis moment. Could other molecules have existed here on Earth to produce life based on a different set of rules? What if life in the Universe could have entirely different molecular origins, each begetting its own Tree of Life?
Today’s biology begins with the tree supporting multiple branches coming from common ancestors. And those representations show a trunk often supported by a bundle of roots; none of the latter represent an alternate molecular derivation.
The theory of alternative biochemistries with different molecules leading to life is called abiogenesis. Here on Earth, DNA triumphed, but what was here before that victory?
Self-replicating RNA (ribonucleic acid), the simpler nucleic cousin of DNA, may have ruled before it took the former’s architecture and bound it to sugars.
Return missions from asteroids have brought back samples containing the nucleic and amino acid components common to DNA and RNA: adenine, guanine, cytosine, thymine and uracil. These samples have also been infused with sugars and thousands of other life-friendly chemicals.
In a pre-RNA and DNA world, we could have seen TNA (threose nucleic acid), PNA (peptide nucleic acid) and GNA (glycol nucleic acid) self-replicating molecules.
DNA’s eventual triumph over the three others mentioned above, other competitors, and RNA may have resulted because it was chemically more complex, which gave it greater flexibility. DNA proved to be more stable during replication than RNA, with lower mutation rates. Then DNA developed a collegial relationship with RNA, an effective partnership that other complex molecules may not have been able to duplicate. It proved to be a winning combination based on what we see here on Earth today.
Is DNA the only molecule in the Universe capable of producing life? In laboratories, experiments have produced synthetic alternatives to DNA. Would DNA likely produce cellular life elsewhere? Changes to Earth’s environment, such as much hotter or colder temperatures, higher radiation exposure, and highly acidic or alkaline water, would have made DNA less likely as the originator of life on Earth.
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]]>On Bennu’s surface were all the precursor ingredients needed for life:
Some might argue that Bennu is a single sample and shouldn’t be considered representative of other asteroids. Except that would be wrong. Samples from the asteroid Ryugu, obtained by JAXA with Hayabusa2, also contained organic molecules, including 15 amino acids. Then there are the carbonaceous chondrite meteorites that have reached the Earth’s surface, which, when sampled, show the presence of amino acids, nucleobases, sugars, and more. These aren’t post-arrival contaminants, but rather being delivered from out of this world. What this more than suggests is that life’s origin isn’t confined to Earth, but rather is a product of the gas clouds and nebula found in the cold environment of space.
A Swedish chemist, Svante Arrhenius, coined the term panspermia back in 1908. He wasn’t the first to propose life’s origins from elsewhere, not Earth. That thought was first expressed by Anaxagoras, a Greek philosopher in the 5th century BCE.
Arrhenius was a pretty smart guy. I’ve written about him before because it was he who described the greenhouse effect, global warming and the correlation between human industrial activity and increases in atmospheric CO₂.
Panspermia comes in several flavours:
Whichever you fancy, the presence of life precursors found on bodies in space other than Earth supports panspermia. If the building blocks of life are everywhere in space, the panspermia argument holds water.
Abiogenesis presents an alternate theory. It proposes that life emerged during Earth’s early history. Probably between 4 and 4.5 billion years ago, as the numerous collisions of protoplanet bodies formed Earth and its atmosphere, conditions for abiogenesis emerged.
Early Earth was hot. Geologists call the period the Hadean Eon, taking the term from the Greek hellish underworld. The atmosphere was mostly CO₂ and nitrogen (N₂), with significant water vapour (H₂O) and smaller amounts of methane (CH₄) and ammonia (NH₃). The crust cooled. The first oceans emerged.
The conditions to lead to abiogenesis were there with sugars and nucleobases combining to produce the RNA World hypothesis, self-replicating RNA, followed by the emergence of proteins, which then “begat,” borrowing a term from Genesis, DNA.
Other sources associated with the abiogenesis theory for the origins of life on Earth point to niche environments that may have been the catalyst. Hydrothermal vents are one, and wet-dry cycles impacting surface ponds are another. Theoretically, both could have produced concentrated organics with the right chemistry to fuel self-organizing, prebiotic reactions to link amino acids to RNA.
A 2025 paper published in Astrophysics presents a hypothesis with 10:1 odds that life rapidly emerged on Earth under these “favourable” conditions.
In the end, both panspermia and abiogenesis could equally be right in a Universe filled with rich molecular chemistry and conditions suitable for life to emerge over billions of years.
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]]>What is clear is that the building blocks for life, including water, carbon molecules, and other chemistry, were present within a few million years after the planet formed.
The common theory for life’s origins is called abiogenesis. It states that simple organic molecules, through natural chemical interaction in the presence of one or more energy sources, provided the spark.
At University College London (UCL), scientists recently conducted an experiment attaching amino acids, which form proteins, to RNA, the single-strand cousin of DNA. Amino acids don’t have the capacity to make copies. RNA, however, can facilitate this, and with this experiment, which included a likely present chemical energy source found on the early Earth, the researchers created a protein factory assembly line.
One of the researchers is Matthew Powner, a professor of chemistry at UCL. He believes the UCL research shows how RNA could facilitate “the first part of that complex process” of protein synthesis. Using simple chemistry, in the presence of water with a neutral pH, Powner describes the result as a chemistry that “is spontaneous, selective, and could have occurred on the early Earth,” nearly 4 billion years ago.
Past experimental attempts to mate RNA with amino acids failed to work. The UCL researchers took inspiration from biology, employing what they described as a gentler approach, employing a thioester, “a high-energy chemical compound important in many of life’s biochemical processes.”
Thioesters in human biochemistry are used in cells for energy storage and during the metabolism of carbohydrates, lipids and proteins. Acetyl-CoA is a thioester functioning as the central hub in cellular metabolic processes. Thioesters also interact with proteins to help regulate cellular function. They are highly reactive and efficient in the synthesis of fatty acids, steroids and other biomolecules. They release energy, making them a likely candidate to produce the spark needed for the emergence of life.
Powner describes the UCL study as uniting “two prominent origins of life theories, the RNA world, where self-replicating RNA is proposed to be fundamental, and the thioester world, in which thioesters are seen as the energy source for the earliest forms of life.” On the early Earth, the thioesters and amino acids would have reacted with a sulphur-bearing compound called patetheine, which previous UCL research shows could have been present.
Although the study doesn’t quite get us to life’s emergence, it does take us closer to that moment, showing how chains of amino acids, essential for life, would have been given the means to replicate, eventually leading to DNA.
For the Earth’s first three billion years of existence, life consisted of single-cell organisms. The fossil record shows stromatolites, mats of photosynthetic cyanobacteria, dating back as early as 3.7 billion years ago in Greenland and 3.48 billion years ago in Western Australia. These represent the oldest evidence of microbial life on Earth and exist as living fossils today, appearing not to have changed from their ancestors. We know these fossils do not represent multicellular life because our analysis of modern stromatolites shows that the DNA and molecular structures of individual cells are consistent with individual autonomy.
The fossil record, however, provides evidence of multicellularity (orthogenesis) occurring at least 20 times between 1.5 and 2 billion years ago, according to a paper published in Biological Reviews in July 2023. Multicellular structures have been identified in early fungi and parasitic microorganisms such as Oxymonada or Parabasalia found in the gut of termites, cockroaches and even humans.
So, how did multicellularity come about? Multicellularity requires different types of cells to adhere to one another, exchange biomolecular signals, and coordinate gene expression to produce common replicable outcomes. Scientists believe that the properties of multicellularity had to appear in single-cell organisms before multicellular species emerged. Some believe that the frequency of retries points to this.
Two research teams, one at the University of California-Berkeley, California (UC-Berkeley), and the other at the Institute of Evolutionary Biology in Barcelona, Spain, have modelled the evolutionary steps of eukaryotes, life based on cells with nuclei. That includes everything from amoebae and paramecia to corals, jellyfish, fungi and moulds, plants, insects, spiders, amphibians, reptiles, birds, mammals and us.
When examining single-cell eukaryotes, such as amoebae, we can observe social characteristics that activate in response to environmental stress. Social amoebae will form colonies and appear to coordinate their activities as if they were a single multicellular species. In 2002, it was discovered that C. owczarzaki, an amoeba found in freshwater snails, can go multicellular by forming clusters of individual amoebae. These are single-celled animals that coalesce to become a superset of themselves, working in coordinated fashion.
Another example of multicellular expression happens with a single-celled choanoflagellate (single-celled organisms characterized by having a long tail or flagellum) called Salpingoeca rosetta. In the presence of a prey bacterium, it divides into daughter cells to form a singular multicellular colony shaped like a rosette (hence the name). In its centre, this multicellular creature hosts several distinct free-living cell types.
Both of these behaviours are different types of demonstrations of the path that led to the emergence of multicellular life from 600 million years ago. One wonders how many other natural experiments to create multicellularity failed along the way and how many we will eventually yield from the fossil record.
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]]>But we may have unlocked the mystery of life’s creation in a paper published in the Proceedings of the National Academy of Sciences (PNAS) of the United States this week. Scientists from the Ludwigs-Maximilian Universitat in Munich, the Brookhaven National Laboratory in Upton, New York, and the University of Illinois in Urbana-Champaign, argue that the origin of life emerged out of randomness in the early Universe, and here on Earth. Molecular structures assembled spontaneously through random interactions leading to a process of sequencing that ultimately became alive. Darwinian principles of natural selection governed this molecular behaviour throughout.
The field of abiogenesis, life from inanimate matter, theorizes how life arose from non-living organic compounds. The first modern attempt to demonstrate this occurred in a laboratory in 1952 when two scientists tried to replicate abiogenesis in a laboratory beaker by exposing a solution of inorganic compounds to the equivalent of lightning, and radiation, while simulating early Earth atmospheric conditions. After allowing the chemical stew to “evolve” over time, amino acid compounds emerged. These were seen as precursors to life. The new paper described above refines the details of that beaker experiment by applying significant computer modeling and experimentation to the process.
Dieter Braun, from the Ludwigs-Maximilian Universitat, describes what he and his fellow researchers did:
“Our experiment starts off with a large number of short DNA strands, and in our model system for early oligomers, we use only two complementary bases, adenine, and thymine. We assume that ligation of strands with random sequences leads to the formation of longer strands, whose base sequences are less chaotic.”
The oligomers referred to above describes a molecule that consists of repeating units derived and incorporated from smaller molecules into it. Using human genome analysis the research team confirmed that out of disorder or randomness, organized sequences naturally evolved.
Primordial Earth would have had a vast number of oligomers evolving from random molecular interactions in the chemical soup within our atmosphere and oceans. What the researchers demonstrated is that oligomers naturally tend to form helical, double-strand structures over time as they interact. One of those helical, double-strand structures is what we know of as DNA. In their experiments, they used adenine and thymine, two of the four base chemicals that we know make up DNA to demonstrate chemical natural selection.
When Darwin theorized about the power of natural selection he based it on observations seen in nature, not on selection coming from inanimate chemistry. But it appears that the chaos of the early Universe and the primordial Earth may have led to the rise of molecular complexity that became life. The two are inextricably linked: that out of chaos emerged animate order with natural selection, mutation, and all that it entails contributing to what is alive here on Earth, and likely elsewhere in the Universe.
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]]>In space, we find evidence of sugars and amino acids floating among the ten sextillion stars of the observable Universe. In endless collisions, these molecular compounds intersect and join together randomly combining to a point where 40 to 100 form chains. These chains with their right-handed and left-handed opposite characteristics can combine to form the dual helical construct that we know of as DNA. It is this natural homochirality that makes self-replication possible and, therefore, life as we know it. If there is other bases for forms of life unknown to us, it may come from combinations of molecules less or more complex than RNA, and DNA. One cannot rule out, then, that our form of DNA-based life is just one of many other life-creating molecules using left and right-handedness attractors to become self-replicating.
The process by which life spontaneously formed in the Universe is called abiogenesis, the organizing of inanimate and inorganic matter into living things. Most of us who haven’t been reared on a religious diet of life’s biblical origin, think abiogenesis happened here on Earth shortly after the planet formed some 4 billion years ago. But it would appear that the conditions for life to form came from space and not from Earth. This origin of life theory is called panspermia, the migration of life to Earth where it found a hospitable environment conducive for it to take root and expand to the more than 7.7 million species that we know of today.
The panspermia theory comes in several flavours. In one or more it is believed that life hitched a ride to Earth either on comets, asteroids, or on rocks blasted from the surface of other planetary bodies that found their way to the early Earth. Another flavour believes life was deliberately planted here by intelligent beings from elsewhere in the Universe with no explanation on how these beings came into existence. This latter version of panspermia theory aligns with those who believe in biblical creation, but in this case life doesn’t come from God, Creator of the Universe.
For those who argue that panspermia came to Earth from another planet, there appears to be evidence that Mars may have been the seed bearer. Mars in the early Solar System may have been a more benign and suitable place for life than Earth. And with Mars’ orbit positioned outside of Earth’s, it was 100 times more likely that a rock seeded with life would travel inward to the surface of our planet rather than the other way around. These panspermia advocates point to evidence gathered from our exploration of Mars and from a meteorite designated ALH84001, identified as from the Red Planet and found in Antarctica in 1984. Some astrobiologists believe the meteorite shows primitive fossils. Others dispute these conclusions. But from rovers on Mars and orbiters above it, we are building a picture of Mars today and in the past. We have detected organic molecules on the planet’s bone-dry surface, the evidence of surface water from the past, and outgassings of methane that are seasonal in nature. All are promising signs of both ancient and possibly even modern microbial life on Mars.
The latest research on the chemistry of RNA adds credence to the theory of life from space well before arriving on Earth. It suggests that the building blocks of sugars, carbon, phosphates and nitrogenous bases, go back to the very earliest days of the Universe during the period of rapid inflation and coinciding with the birth of the first stars and planets, a mix of interstellar chemistry that evolved post-Big-Bang. The research also indicates the importance of homochirality within the chemistry leading to the molecules RNA, DNA, and possibly even other non-Earth biological constructs producing very different forms of life we have yet to discover.
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]]>How does this differ from other explanations of the origins of life? Most theories point to RNA as the precursor to the evolution of living things. Professor Blaber believes that proteins came first made from amino acids that interacted with the extreme salt and heat conditions on early Earth. The Earth of 4 billion years ago was largely salty oceans and volcanic land masses with the hot and almost boiling atmosphere largely comprised of CO2 and nitrogen. Blaber states, “for life to exist in such environments it is essential that proteins are able to adapt in those conditions. In other words, they have to be able to fold.”
The diagram below illustrates how a linear chain of amino acids folds into a three-dimensional shape to form a protein. In biological entities folding is governed by helper proteins. But in the early environment of Earth a few amino acids spontaneously folded in the high salt conditions prevalent on the planet.
Comets and asteroids more than likely brought early amino acids to Earth. We know this because when we study the chemistry of space we find evidence of amino acids in the night sky. And we also find this evidence in meteorites that strike the Earth from time to time. So amino acids are common to the chemistry of our Universe. And of the 20 amino acids commonly found in our bodies, 10 predate Earth and all living things. We call these amino acids prebiotic, meaning before life. These 10 can be made through chemical interactions not requiring biology.
How did Blaber and his team derive their hypothesis and draw their conclusions? They used top-down symmetric deconstruction, a methodology to identify the building blocks of proteins. They were able, therefore, to identify 12 precursor amino acids. According to Blaber that get them 80% of the way to proving their theory of 10 amino acids being responsible for abiogenesis, the spontaneous assembly of proteins leading to biosynthesis and life.
Blaber and his associates published their findings recently in the February issue of the Proceedings of the National Academy of Sciences of the United States of America.
To get a better understanding of the role of amino acids and foldable proteins view this YouTube posted video. What you are watching represents the building blocks that have led to us, at least according to Blaber. Some who cast doubt on this hypothesis point out that in most living cells salt is excluded from the internal environment. But as we find more extremophiles, we are beginning to find evidence that some living things tolerate being immersed in environments in which salt permeates living cells.
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