A Blog by Robert Krulwich

Noah (and his ark) Updated, Improved for Our Time

Instead of the Noah you know, the one who built the ark, sheltered all those animals, sailed for 40 days and 40 nights and got to see God’s rainbow, instead of him, I want you to meet a new one. An updated version.

This Noah shows up in a tough little essay written by Amy Leach, of Bozeman, Montana, who knows her science, knows there’s a flood coming—a flood of humans, seven billion and counting, already swamping the Earth, crowding the land, emptying the sea, and her more modern Noah—informed, practical, not inclined to miracles—has a different plan. He announces,

water color painting with text reading ''unfortunately, animals. we are not going to be able to bring all of you with us this time.''
Illustration by Robert Krulwich

The old Noah, you may remember, squeezed eight humans (wife, kids, their spouses) and at least two of every critter, big and small, onto his crowded ship. But the new Noah, being more practical, feels he can winnow a little. “Everybody” is a lot of animals, more than you know. Back in the day, Amy Leach writes,

pink watercolor background with two drawings of frogs peeking up over the text, which talks about what it would be like to bring two of every creature onto noah's ark
Illustration by Robert Krulwich

And, honestly, (I’m thinking to myself), if the world lost a scorpion or two, would anyone notice? Or want them back? And blotchy toads, biting little flies—some animals are hard to keep going on a tight, crowded ship. On the last voyage, dormitory assignments were beyond difficult.

And all those supplies? Amy Leach writes how the first Noah would have had …

a yellow watercolor background covered with text about collecting food for animals
Illustration by Robert Krulwich

This doesn’t mean we don’t care, new Noah says to the animals. We definitely, absolutely want to bring a bunch of you with us. But, we’ve got to be practical.

Even if our ark has grown to the size of a planet, carrying everybody through is not going to be logistically possible, which is why, he says,

blue watercolor background with black text on it about being in charge of a future noahs ark where not all animals are included
Illustration by Robert Krulwich

And anyway, that first Noah? He lived in a different age, a time they call the Holocene, before humans began to dominate and crowd out the other species. Back then, there weren’t as many people. And there were more kinds of animals, closer by, hiding in the woods, clucking in the yard, so the world was more various then, more intimate, more riotous, and thinking about it (a little wistfully, if only for a moment), the new Noah quietly recalls that on that first ark …

yellow watercolor background with text on top related to how noahs ark would be different today than it was in the Old Testament
Illustration by Robert Krulwich

And now, animals, it’s time for many of you to step away. You’ve had your unruly eons. They were wild, unplanned, noisy, great fun. Natural selection ran the world. Crazy things happened. Those were good times, Amy’s essay concludes …

blue watercoor with black text on top that reads''But the future belongs to us.''
Illustration by Robert Krulwich

Amy Leach is a writer living in Bozeman. Her collection of very short pieces—about jellyfish, beaver, salmon, plants that go topsy turvy and stand on their heads—are collected in a wonderful little book called “Things That Are.” In this column I do to Amy what the new Noah is doing to our planet: I edited her down, sliced, diced, slimmed (lovingly, I hope), trying to give you a taste for her fierce, crazy prose. But like the planet, she’s wilder in the original, so I hope you go there and sample the unedited version.

A Blog by Carl Zimmer

Life Under A Faint Sun

If you could have looked up at the sky 4 billion years ago, you would have seen a sun much dimmer than ours today. And if you looked down at the Earth’s oceans, you would have seen an expanse of bobbing waves.

That’s a problem–a simple one, but a big one. And scientists have been wrestling with it for fifty years.

The brightness of the sun over the past 4.5 billion years. From Feulner 2011 http://arxiv.org/abs/1204.4449

The evidence for these two facts about the early Earth–a dim sun and liquid oceans–were already strong in the 1960s. Astronomers have compared our sun today to other stars of different sizes and ages, and they’ve been able to reconstruct much of its history. The sun started out about 70% as bright as today. It slowly grew brighter; even two billion years ago (2.5 billion years after the Earth formed), the sun was still just 85% as bright as today.

On its own, the faint young sun could not have kept the Earth from freezing over. And yet there are lots of signs in ancient rocks that the Earth was wet. Tiny crystals dating back over 4 billion years have a chemistry that required liquid water. Ancient rocks known as pillow lavas must have formed as molten Earth oozed out into sea water.

As early as the mid-1960s [pdf], scientists realized that these two lines of evidence posed a paradox: what is now known as the Faint Young Sun Paradox. It was a serious problem that required serious thought. It didn’t just mean that the evidence from geology and astronomy wasn’t meshing together. It also added a puzzle to the rise of life on Earth. Life would have had a hard time getting started on a planet of ice.

In 1972, Carl Sagan and his colleague at Cornell George Mullen proposed a solution to the paradox: the greenhouse effect. When radiation from the sun hits the Earth, some of it bounces back into space, but some of it lingers, thanks to heat-trapping gases in the atmosphere. The early Earth would have released gasses from its rocks, creating the first atmosphere. If it had the right chemistry, Sagan and Mullen argued, it might have been able to keep the Earth warm enough to melt ice. They suggested ammonia as a plausible heat-trapper on the young planet.

Unfortunately, ammonia turned out to be a bad solution. Other scientists figured out that ultraviolet rays from the sun would have destroyed any built up ammonia in the atmosphere in less than a decade. That’s not much of a defense against the deep freeze.

But ammonia is not the only greenhouse gas in the game. Today, carbon dioxide and methane are two important molecules keeping our planet warm (and warmer). Scientists have tried for years to narrow down the possible range of the two gases on the early Earth. It’s a very tricky puzzle, because scientists know that there are many factors that can influence their concentrations. And there were factors on the early Earth that we don’t experience today, such as a fairly steady bombardment of comets and giant meteors. Making matters even more complicated, greenhouse gases are not always greenhouse gases. Once the proportion of methane to carbon dioxide gets too high, it produces an organic haze that bounces radiation back into space, cooling the planet.

The consensus today is that methane and carbon dioxide may have warmed the early Earth a fair amount, but not enough to solve the paradox. So scientists are looking at other possible factors. Clouds may have helped. The early Earth rotated quickly through a 14 hour day, which may have changed how the oceans circulated–and thus how they trapped heat. But wide scope still remains for more ideas.

Today in Science, Robin Wordsworth and Raymond Pierrehumbert of the University of Chicago offer two new players to the Faint Young Sun game. They argue that a pair of molecules that have hitherto been neglected–hydrogen (H2) and nitrogen (N2)–could have made up a lot of the difference between the sun’s feeble glow and the Earth’s life-sustaining warmth.

There’s hardly any molecular hydrogen in our atmosphere today, because it easily skips out of the atmosphere into space. But Wordsworth and Pierrehumbert argue that such an escape would have been much harder for hydrogen on the early Earth, partly because it couldn’t get as big of a boost from ultraviolet rays from the sun. They estimate that hydrogen could have made up as much as thirty percent of the atmosphere. They also argue that nitrogen levels were three times higher than today.

On their own, nitrogen and hydrogen don’t do a very good job of trapping the sun’s heat. But when they crash into each other, their structure briefly changes, allowing them to absorb radiation. Wordsworth and Pierrehumbert built a model of a hydrogen and nitrogen-rich early atmosphere and found that as the molecules crashed into each other, they soaked up a lot of heat–enough, they argue, to heat the planet 10 to 15 degrees centigrade. That would go a long way to resolving the Faint Young Sun Paradox.

This new study probably won’t bring the fifty-year debate to a halt. In an accompanying commentary, James Kasting at Penn State argues that nitrogen is too heavy to absorb much radiation, even in the midst of a collision. Instead, Wordsworth and Pierrehumbert are stocking the cabinet that aspiring chefs can raid when they are trying to come up with new recipes for the early Earth.

If hydrogen and nitrogen do turn out to be part of the answer to the Faint Young Sun Paradox, they may have some fascinating implications about life on Earth–and elsewhere. Molecular hydrogen is fine dining for certain types of microbes known as methanogens. As soon as they evolved, they would have been able to feast on a sky full of hydrogen. By devouring the Earth’s protective hydrogen, they might have cooled the planet until it experienced its first glaciers. And beyond Earth, we may need to expand our concept of what kind of planet could support life. If they turn out to have a rich supply of hydrogen and nitrogen, they may offer a toasty incubator for aliens.

Image: “The ‘Fighting Temeraire’ Tugged to her Last Berth to be Broken up” by William Turner, via Wiki-Paintings

A Blog by Carl Zimmer

Life with a capital L? (Like Zimmer with a capital Z?)

Over on Facebook, David Hillis, an evolutionary biologist at the University of Texas, took up my question as to whether anyone can define life in three words. His short answer was no, but his long answer, which I’ve stitched together here from a series of comments he wrote, was very interesting (links are mine):

Like all historical entities (including other biological taxa), it is only sensible to “define” Life ostensively (by pointing to it, noting when and where it began, and following its lineages from there) rather than intensionally (using a list of characteristics). This applies to the taxon we call Life (hence capitalized, as a formal name). You could define a class concept called life (not a formal taxon), but then that concept would clearly differ from person to person (whereas it is much less problematic to note examples of the taxon Life). So, I’d say that I can point to and circumscribe Life, and that it the appropriate way to “define” any biological taxon. A list of its unique characteristics is then a diagnosis, rather than a definition. So, I’d argue that any intensional definition of Life is illogical (does not recognize the nature of Life), no matter how many words are used.

Defining Life (the taxon) is like defining other particular historical entities. We don’t “define” Carl Zimmer or the United States of America by listing out their attributes. Instead, we point to their origin and history. The same should be true for Life. If we ever discover a Life2, we’ll have a new origin and history to point to.

The question people actually want to ask is “Are there entities in the universe that are similar to the Life we know about here on Earth?” The answer, of course, depends on what people mean by the arbitrary meaning of “similar”. One person might answer “I mean ‘self-replicating with variations’.” Then, the answer is yes: humans have created imperfectly self-replicating systems (“artificial life”) here on Earth. But then someone else says “But that is not what I meant by similar…I meant that they had to have metabolism and cellular structure and a nucelic-acid-based genetic system.” OK, then we have to keep looking to find something that similar. But then someone else says “But that’s pretty arbitrary…I’d still consider it alive if it didn’t have cellular structure.” Exactly…it is indeed arbitrary to argue over how similar something has to be to consider it “similar” to Life. So, in the end, we can ostensively define Life (by referencing its origin and history), and we can do the same for other historical entities that some people might also want to say are alive, but there can be no simple “right” answer that will satisfy everyone about which entities should be considered alive, because we all emphasize different characteristics in defining an arbitrary class concept of “life”.

A Blog by Carl Zimmer

Can you define life in three words?

We are all sure we know what life is, but if you try to actually define it, things get tricky fast. I wrote a feature about the scientific struggle to define life in 2007 for Seed, and I’ve been keeping tabs on the evolution of this metaphysical quandary ever since. I was particularly intrigued to discover recently that one scientist thinks he can define life–and do so in just three words. I’ve written an essay about his short and sweet definition for the web magazine Txchnologist. Check it out.

A Blog by Carl Zimmer

Arsenic life and all that: My new book review for the Wall Street Journal

The Wall Street Journal recently asked me to review a new book called First Contact: Scientific Breakthroughs in the Hunt for Life Beyond Earth. Astrobiology is a tricky subject to write about these days. It’s intensely exciting, despite the fact that its main object of study–life on other planets–has yet to be discovered.

I’ve given some thought to how we journalists should cover such a paradoxical science. We shouldn’t dismiss it outright, because astrobiologists have discovered fascinating things about life here on Earth, even if they have yet to find aliens. Yet we shouldn’t feel obligated to pump up every claim about the possibility of life elsewhere. We should be content to paint a portrait of the scientific process–including the intense debates–in all its gorey detail.

By this measure, I don’t think First Contact works. The author, Marc Kaufman, declares at the outset of the book that “before the end of this century, and perhaps much sooner than that, scientists will determine that life exists elsewhere in the universe.” Not whether life exists, mind you, but that it exists.

I don’t think he backed up that bold claim. Instead, he pumps up intriguing, but inconclusive, evidence. He portrays the scientists who made claims for arsenic life, for example, as bold, out-of-the-box thinkers, and criticisms as little more than the rants of bloggers. He’s not alone–on Thursday, Time picked a member of the arsenic life team as one of their 100 most influential people of 2011. But these portrayals don’t match the reality of the arsenic life saga. I find the manufactured dichotomy between the supposed mavericks and the mean-spirited critics to be particularly off target. Remember, a lot of the critics of arsenic life are astrobiologists themselves.

For a better example of how to embrace scientific debate, check out Richard Panek’s The 4 Percent Universe: Dark Matter, Dark Energy, and the Race to Discover the Rest of Reality which I reviewed for the Washington Post in January. Panek doesn’t shy away from the intense competition and bad-mouthing that cosmologists engaged in as they rushed to establish the deep mystery of the universe. It’s a rich story that doesn’t shy away from the messiness and uncertainty that the big questions in science inevitably create.

A Blog by Carl Zimmer

Of arsenic and aliens: What the critics said

A lot of people are interested in my Slate story yesterday on the arsenic aliens. It’s still the most-read story of the site at the moment, Slashdot and others have linked to it, and I’m doing some more radio and maybe other media (details to come).

I think that what has gotten so much attention to the story is just how many scientists had such critical things to say. The verdict was not unanimous, but the majority was large. I was only able to quote a tiny bit from just a few of the scientists I communicated with, so I thought, for those who’d like to delve more deeply into this, that I’d post a list of everyone I spoke to, and, when possible, post their reactions. A lot of scientists replied to me by email or even attached word files where they went on at length. I put together a similar dossier for another biological controversy–the search for soft tissue in dinosaur fossils–and I think (or at least hope) that this sort of exercise can help further discussion.

Of course, as I and others have reported, the authors of the new paper claim that all this is entirely inappropriate. They say this conversation should all be limited to peer-reviewed journals. I don’t agree. These were all on-the-record comments from experts who read the paper, which I solicited for a news article. So they’re legit in every sense of the word. Who knows–they might even help inform peer-reviewed science that comes out later on.

I’m going to post everything under the fold here, but it will take a little while. I’ll just re-save the post every time I add a new one, and I should be done before too long. So keep refreshing, or just drop by again later…

PS–Science has made the paper at the center of this controversy free. Get it here.