How (every single one of) Your Ancestors Survived

There are good days and there are bad days, but by any measure the period around 3.9 billion years ago was the worst time to be living on Earth–or for that matter anywhere else in the solar system.

Ouch! A temperature map of the Earth 4 km below the surface during the thick of the Late Heavy Bombardment. The high temperature region in the center was created by a 300 km-size impactor which produced a crater ten times larger. The blue region shows where temperatures only reached 110°C. That's well within the range of thermophiles today. The rock above this blue zone would have been even more hospitable to liquid water and life.
O. Abramov, University of Colorado, Boulder
This is the period known as the Late Heavy Bombardment (LHB), when giant chunks of debris were let loose to batter the inner planets. No obvious traces of this terrifying episode remain on Earth, but we know it occurred thanks to the Moon. The circular features that give the man-in-the-moon its hollow-eyed expression are the marks of giant impacts that all date to around this time. Earth, with its larger surface area and stronger gravity, would have attracted even more big blows.

How bad was it? Estimates suggest about 50 objects at least 100 kilometers across pummeled the Earth during the LHB. (For comparison, it was a single 10 kilometer-diameter asteroid that is believed to have taken out the dinosaurs.) These are ocean-vaporizing events that would have liquefied large swaths of the planet’s surface.
Yet, despite all this, Oleg Abramov and Stephen Mojzsis say that life survived.

The two University of Colorado, Boulder researchers created a simulation of the Late Heavy Bombardment to study its effects on the temperature of the Earth’s crust down to a depth of four kilometers. (Today bacteria have been detected at comparable depths.) Not surprisingly they found that regions directly hit by an impact would have been sterilized of micro-organisms, the only possible life around at that time. But—surprisingly—a few thousand kilometers away, Earth’s crust would still be stable and capable of supporting ancient bacteria.

Some of those bacteria may even have thrived during the bad years. The giant impacts would have fractured Earth’s crust, creating passageways for hot magma and hydrothermal vents. This is the sort of environment that heat loving organisms known as thermophiles like best.

And it appears they would not have been alone. The study shows that even mesophiles, which require temperatures between 20° and 50° Celsius, could have found ample refuge to ride out the worst of the bombardment and survived to recolonize the planet.

There are at least two interesting implications to this. The first is that life on Earth may be older than we think. Because the Late Heavy Bombardment was so extreme, it’s been previously speculated that it wiped the planet clean of life. Now Abramov and Mojzsis say that’s not what happened.

The earliest (isotopic) evidence for life on Earth dates back to 3.83 billion years ago. That’s getting uncomfortably close to the Late Heavy Bombardment and it doesn’t give life much time to get started from scratch. But if life was already present well before the Late Heavy Bombardment, there’s less of a mystery about how it got going so fast.
The second implication is for life elsewhere in the solar system and beyond. If life on Earth could survive the Late Heavy Bombardment then presumably life on Mars could too. So could life on other planets in other solar systems where the same bombardment scenario may have occurred.

Life is funny that way. Getting it going must require just the right conditions and plenty of time—otherwise someone would have seen it spontaneously come to be in a lab somewhere. Yet, once life is established, it seems like you just can’t keep it down.
For my money, British rapper Michael Skinner (aka The Streets) says it best in his song “On the Edge of a Cliff”:

For billions of years since the outset of time
Every single one of your ancestors has survived?
Every single person on your mum and dad's side?
Successfully looked after and passed on to you life.
What are the chances of that, like?
It comes to me once in a while?
And everywhere I tell folk it gets the best smile.

The results of the new study were published last week in Nature. For more on this and other revelations about the origins of life, there’s an interview with Oleg Abramov in the next episode of The Universe in Mind podcast.

Ivan Semeniuk is host of The Universe in Mind podcast and a science journalist in residence at the Dunlap Institute for Astronomy and Astrophysics, University of Toronto.

14 thoughts on “How (every single one of) Your Ancestors Survived

  1. Rod

    Apparently the philosophy here explains the origin of life on earth and how mankind originated, escaping destruction during the LHB. Note philosophy, not science. Here are some hurdles to overcome for those espousing this philosophy concerning origins.

    1. The origin of the Earth-Moon system from dust grains in an accretion disk around the Sun.
    2. The origin of life from non-living matter by spontaneous generation-the first living cell.
    3. The origin of multicellular life, e.g. Precambrian algae.
    4. The origin of invertebrates during the Cambrian explosion from Precambrian microorganisms.
    5. The origin of vertebrates-the fish from invertebrates in the fossil record.

  2. Phil

    Rod, I have read and re-read your post and still cannot figure out what you’re saying. Assuming you’re not some creationist nut-job trying to confuse everyone by spewing scientific-sounding jargon, all I can do is restate what the article is about: life did not necessarily /have/ to (re)start after the LHB. There’s a good possibility that, if life had started earlier, it could have survived the LHB. It would mean that (1) life is durable and (2) it didn’t have to start so quickly as to be going by 3.83 Gya. Anyway, nothing’s proved one way or the other, and will likely never be. That’s the way of science. Absolute certainty is for religion. Now, what were you saying?

  3. Richard Sauder

    You are sounding like an evolutionist.
    Did you realize that it is just as impossible for Life to be cooked up by random chemical means as it is for Lead to be stewed into Gold by chemical means?
    Why? Because “it just isn’t done that way.”

    Lead can only be converted into Gold by nuclear means, if that. And, Life can only be created by informational means. You have heard of the DNA code, have you not?

    Consider this . . . There are fewer than 474 quadrillion seconds of time in 15 billion years. And, there are more than 1,152 quadrillion different ways to arrange just 30 nucleotides in a DNA molecule. Since we have about 3 billion nucleotides in our Human DNA, and the amoeba has about 670 billion nucleotides, when do you suppose that all of this exquisite organization took place? Especially, by random chance in small successive variations as our buddy, Darwin suggests. Certainly not in 2 or 3 or even 15 billion years!
    I believe you must have more faith in your religion than any dozen Creationists have in theirs’!
    Personally, I would rather stick to true science than fuss about something you will never be able to prove anyway.

  4. Phil

    Dear Richard. Bite me.

    Your religious claptrap is the reason I do not belong to any organized religion. What is this ‘true science’ you claim? It’s certainly nothing that any actual scientist like myself would recognize. Did you mean to type ‘true faith’?

  5. Jose A. Fadul

    Dear Phil,
    I would say not “survival of the fittest” but “survival of the fit enough”. Otherwise we are all just one species today.

  6. Richard Sauder

    Dear Phil,

    My comment was not meant to be a discussion of religion. I am sorry I mentioned a word you may have misunderstood. I am sure you have a scientific calculator. Can you disprove any of the concepts that I have offered? I understand that the facts I have shared are generally accepted scientific truth. If you can disprove any of it, I am willing to stand corrected.

  7. Jim Lindelien

    Prior research has shown that amino acids form spontaneously by thermodynamic processes that would have been common on the early earth. More recent research suggests strongly but does not yet prove that RNA will self-assemble, again in conditions common on the early earth. The notion that RNA, then DNA, can arise spontaneously via normal thermodynamics appears to be where research results are rapidly converging.

    While your math may be correct, you leave out facts that cause your conclusion to be false. For one thing, there’d be a planet-load of informatic molecules floating around, being mutated and selected between, all simultaneously, and in many places along each molecule simultaneously. Many many more orders of magnitude than your numbers would indicate. This represents a powerfully effective search of this large “information space” of possibilities.

    In very simple simulations of this process of mutation, recombination and fitness selection, performed in computer software called “genetic programming” it is observed that the huge information space you describe is searched very efficiently in a short time and a few thousand generations for many optimization (“natural selection”) tasks.

    The fault of your approach is to presume all decisions on the detail of the sequence must be made serially, one at a time, on one molecule. Nature does not work that way, and molecular biologists are frankly not so stupid as to be tripped up by the analysis you provide, as it obviously naive.

    Do your homework and you’ll find the universe is more subtle and beautiful than you now imagine, and is quite capable of spontaneously creating life.

  8. Marjorie A. Walz

    The isotopic evidebce that life existed on Earth 3.83 billion years ago is highly speculative. There was an article on this in Science, the newsmagazine of the American Assn. for the Advancement of Science, vol. 296: pp 1448-1452 (24 May 02). As long as everyone is clear how speculative this is, fine! It’s good speculation, and science begins with “What if…?”

  9. Jim Lindelien

    Richard, if you are truly open-minded and are willing to learn more about the topic of self-organization amid complexity, I refer you first to Stuart A. Kauffman’s excellent and very accessible book,

    At Home in the Universe: The Search for the Laws of Self-Organization and Complexity


  10. Richard Sauder

    Thanks for your level headed comment. I plan to read the book you have recommended, but give me a few weeks! One thing I find hard to imagine is the existence of the “planet load of informatic molecules floating around” that you mentioned. Can such molecules be found running loose today? And if so, where do they get their “informatic” properties? None of the naturally ordered systems that I am aware of include any information at all. (tornadoes, crystals, stalagmites and stalactites, etc.) I am familiar with the Miller/Urey experiment that produced a few simple amino acids. However, I understand that all such experiments yield approximately equal numbers of “right” and “left” handed amino acids which ultimately destroy each other if not separated by the experimenter. If Life is really composed almost entirely of L-Amino acids, does anyone have a theory as to why this is the case?
    I suppose I just believe that organized information does not and cannot exist in the absence of high intelligence. If it does, I would like to hear about it. Since bare information always describes something other than itself, where is the driving force behind coherent organization of information that enables the development of proteins and other building blocks of what is yet to be conceived?
    Again, thanks for your civilized comment.

  11. Peter WilsonPeter Wilson

    “How (every single one of) Your Ancestors Survived”
    How did the theory of reincarnation get into an astronomy article? I don’t think reincarnation is really scientifically testable.

  12. Richard Sauder

    Dear Peter, You make an excellent point. While I do not think this discussion touched on reincarnation, it also certainly had little to do with real astronomical science. All discussions and studies of origins must necessarily be relegated to the realm of the hypothetical. No one can know what the early earth conditions really were, and so the outcome of any experiments based on any suppositions of that rickety knowledge must be subject to much doubt. True science is really thrilling – making repeatable measurements and doing repeatable experiments to discover how things really work in this really wonderful Universe in which we live. But, reports of studies of Origins always generate more heat than light, simply because the outcomes depend heavily on the inputs and the interpretations of evidence. These interpretations are always based on the world view of the investigator. Garbage in . . . Garbage out.

  13. Nathaniel Sailor

    I agree with Phil. The Earth was made 5000 years ago. My family is religous so I was thought that way. And I belive the Earth was made in 5000 years. this 4.4 billion year stuff is a pack full of bull. I don’t care what ya’ll them me.

  14. Mike ODowd

    Richard, I have some questions.
    Can you show us the math you used to determine that there are 1,152 quadrillion different ways to arrange 30 nucleotides in the DNA molecule. The Bubonic Plaque bacterium has a 4.65 million nucleotides sequence and the Malaria Parasite 23 million nucleotide sequences arranged in 5,300 genes. Using your mathematical method, how many different ways are there, to arrange these two genomes or, what is the probability of these two organisms evolving by random chance in small successive variations. Do you realize that if these two contagious diseases and all the others where divinely made, your Creator has created more human suffering and premature death than the Nazis and Communist put together. If not, then where did all the ‘Information’ contained in these organisms come from?

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