Could life have emerged multiple times on Earth, in the universe?

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How did life on Earth arise? Was it abiogenesis — the origin of living forms from non-living matter? Or was our planet merely seeded with microorganisms originating from somewhere else in the galaxy? And if the origin of Earth life was on Earth, did similar events occur on Mars, Venus, Jupiter’s moon Europa, Saturn’s moon Enceladus, and on hundreds of millions of worlds throughout the universe?

The answers to these questions — central to astrobiology and research into the origins of life — could help us in several ways. If we discovered, for example, that life forms on Europa don’t share a common origin with Earth life, this would tell us the cosmos is teeming with life. It would mean that abiogenesis is a common occurrence — since we’d have life emerging independently on two neighboring planets. But also, it would give us a new perspective on biology. That’s because all life on Earth could be assessed as a special case, a system that uses DNA as the information-storage material, and a particular language –the Genetic Code– for making use of that material to control biology.

But there’s one more dimension to the origins of life paradigm. The life that we know took hold on Earth about 3.5 billion years ago. But this does not mean that our system is the only life that emerged on Earth. Nor would it mean that our life is the only one deposited here from space. If abiogenesis happened once on Earth, indeed, if it happened here and on neighboring worlds, there’s no telling how many times it could have happened. We could be the descendants of the system of life that won out over others, either because it out-competed other systems, or because it emerged after other systems went extinct following planet-wide natural disasters.

Multiple origins perspective

In 1953, Stanley Miller and Harold Urey demonstrated that simulated lightning and ultraviolet radiation — forces present on early Earth — could stimulate conversion of simple chemicals into more complex chemicals needed to create life. Since that time, scientists have experimented with a growing number of prebiotic chemistries — systems that are not alive, but full of chemicals that life uses.

Nobody has yet observed life emerging on its own in laboratory simulations of ancient Earth, but researchers have demonstrated various parts of the puzzle. They have shown that amino acids (the building blocks of proteins) form easily. They have shown that the building blocks of DNA and RNA also form easily. Importantly, they have shown that energy-rich chemical bonds needed to support any kind of life are created easily. They have shown that lipids (fat-like chemicals) not only can form easily, but also can organize spontaneously into membranes that can enclose other types of chemicals into primitive cells.

Did life on Earth originate from somewhere else?

The last universal common ancestor can be traced back billions of years by comparison of genetic sequences of various organisms. The fossil record shows solidly that there were organisms on Earth 3.5 billion years ago that looked a lot like today’s photosynthetic bacteria. Consequently, there is little doubt among scientists that our system of life was established by that time period. However, because the pieces of the puzzle — prebiotic chemical reactions and cell membrane organization — occur easily, there’s a growing awareness that our distant, microbial ancestors may not have been alone on this planet.

There have been several mass extinction events over the last few billion years, so it is plausible that competitors of organisms with the genetic system that we inherited were wiped out. It’s also plausible that some other system of life still exists deep in the Earth’s crust. Furthermore, Earth’s surface was cool enough to support life beginning about 3.9 billion years ago and certain rocks from Greenland contain chemical isotope evidence for the presence of life 3.8 billion years ago. This means evidence related to the numbers of neutrons in the atoms of certain chemical elements. That tells you nothing about genetics, nothing about physical form. Consequently, it leaves a period of few hundred million years, on Earth at least, when there could have been life very different chemically from the life that we know, yet with no way for us to know anything about its nature.

If there could have been two kinds of life on the early Earth, it stands to reason that there could have been more than two. From there, it is logical to predict that various early biological systems could have been on Earth in that early time, and also on other worlds in the solar system.

David Warmflash is an astrobiologist, physician and science writer. Follow @CosmicEvolution to read what he is saying on Twitter.

 

  • petergkinnon

    Sadly, as we see here, much of the scientific community is still embedded in the long discredited “primeval soup” paradigm.

    None of the DNA first, RNA first, protein first or cell membrane first models are truly compatible with established laws of chemistry and physics.

    As far back as 1986 Robert Shapiro’s book “Origins, a Skeptic’s Guide to the Creation of Life on Earth” gave an exhaustive and definitive explanation of why this is the case.

    In these exciting times it is becoming widely recognized that the early notion that the first identifiable instances of biology were naked self replicating molecules (strands of DNA, RNA or protein) or “empty” lipid bubbles, is deeply flawed.

    It is unevidenced and, furthermore, cannot even be given a sound heuristic basis. It is one of those myths which has insidiously crept into scientific circles without serious challenge. Along with the equally impractical notions involving panspermia.

    Today, a far more plausible model that is consistent with known principles of physics and chemistry derives from the exploration in recent decades of the deep-sea alkaline hydrothermal vents.

    This model provides for the CO-EVOLUTION of enzymes, nucleotides and, most importantly, that oft overlooked but absolutely crucial component, a cell membrane equipped with means of selective influx of nutrients and efflux of wastes.

    The plumes generated by the vents provide vast matrices of catalytic cell-sized cavities, complete with suitable chemical precursors, flow, and favorable energetics that bring the probabilities within reasonable bounds.

    This scenario is explored at length in chapter 9 of my last book “The Intricacy Generator: Pushing Chemistry and Geometry Uphill”.

    Furthermore we can be reasonably confident of a high probability of biology evolving on other planets where similar conditions exist.

  • qedlin

    The broad speculative propositions made here are strong indication of the dismal failure of naturalist theories for origins of life. With time the scenarios for life’s development are becoming more and more exotic, untestable, and incoherent relative to the empirical evidence. To suggest that there were multiple originations of life in this context is to attempt to trivialize life’s formation so to make it simple and ubquitous. The radiation events during Earth’s chronology are manifestations of non-Darwinian creation of life intended to provide the means for bio-forming the Earth to accommodate sequentially more sophisticated life forms that eventually lead to humans. There is not empirical evidence of any similar activities outside of the Earth.

  • T Kay Kiser

    Speculation upon speculation upon assumptions upon deduction from pure logic of what we think must have happened in the past without adequate or any evidence. Why is an article like this called “Scientific?” It is more akin to the pseudoscientific methods of the antiGMOs, and antiVaxxers. Speculation should be only the beginning of scientific research, not the end product “because it must have been.” The truth is that we know nothing about the origin of life. Even the Miller-Urey experiment, so often touted in the literature, was nowhere near demonstrating that life could arise from dead chemicals. Our ignorance is overwhelming. Unlike popular astrobiological myths, life is not a “given” that will automatically arise in the presence of water. According to our own understanding, life arising from dead chemicals in statistically impossible. It must be extremely rare and probably unique in the universe. Read Robert Shapiro’s 1989 book Origins, A Skeptics Guide to the Creation of Life on Earth for examples of statistical improbabilities and incompatible conditions for forming each of the components of living things.

  • Fracking Saves

    There is one and only one universal rule regarding abiogenesis in this Universe:

    Abiogenesis is impossible and cannot occur under any circumstance anywhere in the entire Universe, and this is true even if the Universe is infinite in size and/or there are an infinite number of universes.

    • Byronic Fate

      what is your evidence?

      • Fracking Saves

        The failure of biologists to generate an abiogenesis event in a laboratory is quite sufficient to prove conclusively that abiogenesis is absolutely and unequivocally impossible.

        But if this argument isn’t convincing enough, it is quite possible that I have access to more information about this subject than is otherwise available to humankind