Book Review — Alone in the Universe: Why Our Planet Is Unique (Part 3)

[ I'm reviewing this book because I liked it, but also for a larger reason which will become evident at the end of Part 3 of the review, and in the weeks ahead. ]

[ Also, in case you missed it: Part 1Part 2 ]

Alone in the Universe: Why Our Planet Is Unique by John Gribbin

What’s So Special About the Earth? Well, for one thing, it was once a great deal smaller, a solitary planet with no moon, until it served as a target for a Mars-sized object. Billiard balls might collide and rebound, but when solid objects the size of planets crash into each other, the effect is more of a molten splash. Earth ended up about 90 percent the size it is today (with more matter, including lots of water, to come in countless minor collisions later). It also ended up with the relatively rapid day-night rotation we enjoy today (although it was quite a bit faster originally), a molten iron heart that powers what amounts to a magnetic force field guarding us from the atmosphere-destroying blowtorch of the solar wind, and a sister-planet (the Moon) that simultaneously helps power active tides and serves as a gravitational stabilizer keeping the Earth’s slightly-tilted rotational axis (the bit that gives us our relatively mild, life-permitting seasons) from varying wildly.

Gribben adds that the evidence suggests the plate tectonics of Earth – the motion of crustal plates that thrusts land up above the surface of the oceans – was made possible by the thin crust that was one result of that massive collision. There’s enough water on the planet that if there were no continents, if the solid part of our world were just a quiescent round ball, water would cover it to a depth of 3 kilometers. Meaning: No land life. The pinnacle of sluggish evolution in that unchanging wet desert of ocean might be jellyfish, or bacteria. Or nothing.

Gribben goes on:

… what this really means is that the single most important factor in making the Earth a suitable planet on which a technological civilization could evolve is the Moon. And Moons like ours are really rare.

A search with the Spitzer infrared space telescope found evidence that might indicate the existence of such a moon in the (possible) solar system of only one of four hundred possible candidate stars.

What’s So Special About the Cambrian Explosion?

Imagine that you stand at the beginning of life on Earth, right where and when the first reproducing cells came into existence, and picture the blithe, confident feeling you’d have as you say, “Oh, intelligent life will always show up sooner or later.”

And then wait 3 billion years for something — anything! — interesting to happen. But nothing does. For 3 billion years. If every year was an inch, that length of time would stretch for more than 47,000 miles.

Seems … odd, don’t you think? I mean there was all this life on Planet Earth, and the same land and ocean and weather and stuff and three billion years passes with nothing to show for it but wimpy little single-celled thingies.

Near the end of the Precambrian, living things finally seemed to evidence some minimal ambition, inventing multicellularity, before finally taking off in interesting ways in the Cambrian explosion (a change of affairs that was probably driven by yet another unlikely accident).

There’s a point here that Gribben makes gently, but that I think should be made more forcefully: If there were any sort of linear inevitability to the evolution of life, some kind of general rule about growth and complexity you’d expect it to be obeyed on every planet with life. So that within a few million years of its appearance, life would smoothly progress into all sorts of cool and freaky new forms.

But it would have happened here too, don’t you think? The one sample of evolution we have seems to show that life comes with no guarantee of complexity. Not for 3 billion years, maybe not ever.

Of course, in our case, there were a few snags along the way. For instance, the Sturtian glaciation, which lasted, Gribben says “for at least 5 million years, and extended to the equator.” (See Wikipedia: Snowball Earth)

Turning away from thoughts about life for a moment, picture this: The entire land surface of the planet covered in ice. The surface of the oceans frozen, right into the tropics. All of that white, white ice reflecting much of the solar radiation right back into space. Once the process got going, for whatever reason, it would, well, snowball, turning Earth into a planetary deep-freezer that would lock in the conditions indefinitely.

The saving grace of Earth may have been volcanoes. Erupting and releasing carbon dioxide that gradually, over millions of years, thawed the deep-freeze and allowed life, which had somehow held on, another go.

But how common can all this be? A planet with a hot core capable of producing molten rock? With a thin-enough crust to allow it within spitting distance of the surface? With plate tectonics rowdy enough that would move that crust around enough for weak spots to develop and sprout CO2-emitting volcanoes? Off and on for millions of years? Hmm.

[ Continued in Part 4 ]

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About Hank Fox
  • http://cornelioid.wordpress.com/ Cory Brunson

    There’s a lot to absorb here, and i hope there’s care taken to avoid some pitfalls of probabilistic thinking — specifically, that the probability of conditions being precisely what they were accurately reflects the probability of conditions being habitable to life at all. We hear an analogous error from creationists who point to all of the specific forks and dead ends evolution had to make in order to arrive at humans, while missing the point that evolution didn’t have humans in mind at the outset. How many ways are there for planets to produce life, other than the very delicate path our own took? How delicate was it, really? Could life really not have arisen and complexified under a slightly different course? (We still hold out hope for life on another snowball in our own solar system — Europa.)

    I hope you and Gribben take a look before it’s over, but in any case i’m enjoying the ride.

  • http://nojesusnopeas.blogspot.com James Sweet

    So far, the key for me here is whether the event that created our moon is really necessary or not. I admit this is not the first time I’ve wondered about that. It seems awfully fishy that, on this only planet we know of where there is life, there is also a moon that rotates at almost precisely the same rate it orbits. Is that important? Or perhaps that trait is epiphenomenal to something else that is important, e.g. the impact changing the rotation rate of the Earth? It really makes me wonder.

    Everything else that is covered so far, I find unconvincing. Yes, okay, there is both a galactic Goldilocks zone as well as a planetary one. Still going to be countless tens of thousands of planets in our galaxy alone occupying both zones. I do think that the timing of the Cambrian explosion suggests that intelligent/complex life may be rare in comparison to simple life, but a) we’re dealing with a sample size of one here, so who really knows; and b) if we do take the course of evolution on Earth as typical, the “rare” in the first clause of this sentence becomes “rare but not exceedingly rare”.

    If we take the history of the Earth as typical for a life-bearing planet (which is a solar system-sized “if”, but let’s run with it) then simple life is common, complex life is rare, but where there is complex life then intelligent life is not at all uncommon. But who knows, it could be that Earth is a fluke in how long it took for complex life to evolve. It could be that complex life is that hard, but intelligent life was a fluke. It could even be that intelligent life is nigh inevitable if you develop simple life early enough in your star’s evolution, but that the fairly rapid appearance of simple life on Earth was a fluke. Without a larger sample size (which we very well may never have*) we are merely guessing here.

    * To reiterate my previous position: I consider it extremely unlikely that we are alone in the universe; I consider it quite possible we are alone in the galaxy but I’d probably bet against even that; however, I think it’s likely we will never make contact with another intelligent civilization. Space is too big, light speed is too slow, and intelligent life is (probably) too rare. I hold out hope that we might detect simple life elsewhere in the solar system (though I would bet against it). And I consider it at least within the realm of the possible that we will one day transform ourselves into/build sentient machines for whom time is plentiful enough that limited interstellar exploration is possible, and in that case we might discover simple life in other solar systems. But I wouldn’t bet on any of those things.

    So I don’t think we are alone, but I don’t think we’ll ever know that for sure.

    • MaryLynne

      Thank you! You expressed so well exactly what I think about it. The author shares some very interesting facts, but every “It’s really rare” or “Probably an unlikely accident” is an assumption with no evidence because we have a sample of one.

      “Only” one out of 400 stars/planets might have a moon like ours? That’s still a whole lot. What if 3 billion years to life is an average, not an anomaly? This post reminds me of the Jehovah’s Witness on my doorstep: He said if there are 400 amino acids, what are the chances that the 20 needed for life would randomly assemble? Very unlikely, therefore God. My reply: But what if those amino acids were sloshing around together for millions of years in all different combinations. Then what are the chances of any particular combination happening? Pretty much 100%, therefore not evidence for God.

      That’s how this book’s arguments look to me. Given the span of time and sample size of billions, it doesn’t look like a reasonable assumption that any event or combination of events would only happen once. As you said, given the span of time and space, it would be a statistical fluke if we ever ran into other life, but it seems unreasonable to think we are alone.

    • http://cornelioid.wordpress.com/ Cory Brunson

      It seems like you’re not really appreciating the insights here. The consequence of considering both Goldilocks zones is not that the likely number of inhabitable planets gets whittled down to a few dozen, but that the Drake number — whatever we might have previously taken it to be — is reduced by a few orders of magnitude. Ditto the delay from unicellular life to complex organisms (which implies that complex life is far from inevitable once simple life has arisen). Moreover, the number of crucial forks leading up to intelligent life indicates not that it could not have arisen by some other path, but just how much randomness determined that path in the first place — complex life *does not* necessarily, or even easily, lead to intelligent life. Intelligent life seems common to us because it propagated widely once it took hold.

      Of course, there’s plenty of wiggle room, but we are whittling down the number of variables we can reasonably play with.

  • gwen

    The premise of the book sounds too much like someone living on Hawai’i saying “Wow, these are perfect conditions for life. I can’t imagine life evolving anywhere other than somewhere where the weather, water and land conditions are exactly thus.” Moving to Nome, Alaska where a person could say “wow, these are perfect conditions for life. I can’t imagine life evolving anywhere other than somewhere where the weather, water and land conditions are exactly thus.” Moving on to the nearest volcanic vent on the floor on the ocean, the inhabitants would ‘feel’ the same way. I think the author assumes Waaaay too much.

    • jamessweet

      I think it’s not quite as bad as that… I think the idea of a planetary goldilocks zone is quite sound, for instance. Our biases may be setting the zone a bit more narrowly than it ought, but certainly you cannot really have the kind of stable chemical reactions necessary for descent-with-modification too close to a star, nor can you have sufficient energy to support the entropy-sucking features of life if you are too far from a star. Similarly, it’s difficult to imagine stable reactions persisting in a region dowsed with ionizing radiation, like the galactic center.

      But yeah… Even those assumptions are provisional, and those are probably the strongest points.

  • Lee from NC

    The whole idea of the moon being necessary for a planet to have both land and ocean is completely negated by Mars. Mars is relatively dry now though it does have some level of permafrost underground. But in the past it had both land and oceans without having been smacked hard by another planetary body and forming a moon.

    And, as I understand it at least, and please correct me if I’m wrong, Mars lost it’s water when it’s atmosphere dissipated. And the atmosphere left mainly when Mars lost its magnetic field. Though we don’t know for sure what happened to the Martian magnetic field (asteroids? planet too small to keep internal heat?).

    Basically, my point being that we have 2 planets right beside each other that both have/had land and large oceans. And if Mars had been bigger or not hit by asteroids, we might have neighbors. So I don’t really buy the moon being necessary for life or even intelligent life.

  • Bugboy

    Of course, preconditions are everything.

    We are talking about WATER based life forms. It’s entirely possible that life may exist in say, an ammonia based system.

    Yes, our planet is unique, if you assume a water based life system is the only way to achieve intelligence.

  • http://www.facebook.com/profile.php?id=100000827478206 jimbaerg

    “magnetic force field guarding us from the atmosphere-destroying blowtorch of the solar wind”.
    I’m very skeptical of the idea that planetary magnetic fields help much in holding onto planetary atmospheres. Venus has no magnetic field but its atmosphere is almost 100 times thicker than Earth’s & the nitrogen in Venus’ atmosphere alone is about 3 times more than Earth’s. Venus did lose the hydrogen in its water but that is due to Venus getting twice as much solar heating as Earth.

    LeeFromNC: I think the fact that Mars has much less gravity than Earth is more important than the fact that Mars has less magnetism.

    James Sweet: “It seems awfully fishy that, on this only planet we know of where there is life, there is also a moon that rotates at almost precisely the same rate it orbits.”

    Actually most of the known satellites of planets rotate at the same rate they orbit their primaries. Tidal locking is the reason.

  • Dunc

    I stick this here rather than on the more recent instalment, as it’s more relevant… Hopefully it will still get noticed.

    I was thinking about this the other day, and it occurred to me that two of the reasons postulated for Earth’s uniqueness may be related in an unexpected way: the planet’s comparative stability, and the length of time it’s taken to evolve something like us. Survival pressures drive evolution, with mass extinctions resulting in the relatively rapid subsequent evolution of new ecosystems. Perhaps the very stability which we think is needed for complex life is actually the reason why it took so long to develop. Perhaps a less stable, more challenging environment would result in the much faster evolution of complex life?