This deep-sea mystery is changing our understanding of life | Karen Lloyd

1,540,436 views ・ 2018-02-28

TED


Please double-click on the English subtitles below to play the video.

00:13
I'm an ocean microbiologist at the University of Tennessee,
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and I want to tell you guys about some microbes
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that are so strange and wonderful
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that they're challenging our assumptions about what life is like on Earth.
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So I have a question.
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Please raise your hand if you've ever thought it would be cool
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to go to the bottom of the ocean in a submarine?
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Yes.
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Most of you, because the oceans are so cool.
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Alright, now -- please raise your hand
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if the reason you raised your hand to go to the bottom of the ocean
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is because it would get you a little bit closer
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to that exciting mud that's down there.
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(Laughter)
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Nobody.
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I'm the only one in this room.
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Well, I think about this all the time.
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I spend most of my waking hours
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trying to determine how deep we can go into the Earth
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and still find something, anything, that's alive,
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because we still don't know the answer to this very basic question
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about life on Earth.
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So in the 1980s, a scientist named John Parkes, in the UK,
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was similarly obsessed,
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and he came up with a crazy idea.
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He believed that there was a vast, deep, and living microbial biosphere
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underneath all the world's oceans
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that extends hundreds of meters into the seafloor,
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which is cool,
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but the only problem is that nobody believed him,
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and the reason that nobody believed him
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is that ocean sediments may be the most boring place on Earth.
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(Laughter)
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There's no sunlight, there's no oxygen,
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and perhaps worst of all,
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there's no fresh food deliveries for literally millions of years.
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You don't have to have a PhD in biology
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to know that that is a bad place to go looking for life.
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(Laughter)
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But in 2002, [Steven D'Hondt] had convinced enough people
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that he was on to something that he actually got an expedition
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on this drillship, called the JOIDES Resolution.
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And he ran it along with Bo Barker Jørgensen of Denmark.
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And so they were finally able to get
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good pristine deep subsurface samples
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some really without contamination from surface microbes.
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This drill ship is capable of drilling thousands of meters underneath the ocean,
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and the mud comes up in sequential cores, one after the other --
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long, long cores that look like this.
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This is being carried by scientists such as myself who go on these ships,
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and we process the cores on the ships and then we send them home
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to our home laboratories for further study.
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So when John and his colleagues
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got these first precious deep-sea pristine samples,
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they put them under the microscope,
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and they saw images that looked pretty much like this,
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which is actually taken from a more recent expedition
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by my PhD student, Joy Buongiorno.
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You can see the hazy stuff in the background.
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That's mud. That's deep-sea ocean mud,
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and the bright green dots stained with the green fluorescent dye
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are real, living microbes.
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Now I've got to tell you something really tragic about microbes.
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They all look the same under a microscope,
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I mean, to a first approximation.
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You can take the most fascinating organisms in the world,
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like a microbe that literally breathes uranium,
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and another one that makes rocket fuel,
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mix them up with some ocean mud,
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put them underneath a microscope,
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and they're just little dots.
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It's really annoying.
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So we can't use their looks to tell them apart.
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We have to use DNA, like a fingerprint,
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to say who is who.
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And I'll teach you guys how to do it right now.
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So I made up some data, and I'm going to show you some data that are not real.
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This is to illustrate what it would look like
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if a bunch of species were not related to each other at all.
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So you can see each species
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has a list of combinations of A, G, C and T,
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which are the four sub-units of DNA,
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sort of randomly jumbled, and nothing looks like anything else,
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and these species are totally unrelated to each other.
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But this is what real DNA looks like,
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from a gene that these species happen to share.
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Everything lines up nearly perfectly.
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The chances of getting so many of those vertical columns
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where every species has a C or every species has a T,
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by random chance, are infinitesimal.
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So we know that all those species had to have had a common ancestor.
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They're all relatives of each other.
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So now I'll tell you who they are.
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The top two are us and chimpanzees,
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which y'all already knew were related, because, I mean, obviously.
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(Laughter)
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But we're also related to things that we don't look like,
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like pine trees and Giardia, which is that gastrointestinal disease
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you can get if you don't filter your water while you're hiking.
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We're also related to bacteria like E. coli and Clostridium difficile,
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which is a horrible, opportunistic pathogen that kills lots of people.
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But there's of course good microbes too, like Dehalococcoides ethenogenes,
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which cleans up our industrial waste for us.
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So if I take these DNA sequences,
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and then I use them, the similarities and differences between them,
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to make a family tree for all of us
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so you can see who is closely related,
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then this is what it looks like.
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So you can see clearly, at a glance,
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that things like us and Giardia and bunnies and pine trees
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are all, like, siblings,
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and then the bacteria are like our ancient cousins.
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But we're kin to every living thing on Earth.
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So in my job, on a daily basis,
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I get to produce scientific evidence against existential loneliness.
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So when we got these first DNA sequences,
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from the first cruise, of pristine samples from the deep subsurface,
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we wanted to know where they were.
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So the first thing that we discovered is that they were not aliens,
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because we could get their DNA to line up with everything else on Earth.
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But now check out where they go on our tree of life.
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The first thing you'll notice is that there's a lot of them.
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It wasn't just one little species
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that managed to live in this horrible place.
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It's kind of a lot of things.
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And the second thing that you'll notice,
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hopefully, is that they're not like anything we've ever seen before.
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They are as different from each other
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as they are from anything that we've known before
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as we are from pine trees.
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So John Parkes was completely correct.
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He, and we, had discovered a completely new and highly diverse
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microbial ecosystem on Earth
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that no one even knew existed before the 1980s.
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So now we were on a roll.
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The next step was to grow these exotic species in a petri dish
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so that we could do real experiments on them
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like microbiologists are supposed to do.
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But no matter what we fed them,
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they refused to grow.
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Even now, 15 years and many expeditions later,
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no human has ever gotten a single one of these exotic deep subsurface microbes
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to grow in a petri dish.
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And it's not for lack of trying.
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That may sound disappointing,
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but I actually find it exhilarating,
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because it means there are so many tantalizing unknowns to work on.
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Like, my colleagues and I got what we thought was a really great idea.
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We were going to read their genes like a recipe book,
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find out what it was they wanted to eat and put it in their petri dishes,
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and then they would grow and be happy.
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But when we looked at their genes,
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it turns out that what they wanted to eat was the food we were already feeding them.
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So that was a total wash.
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There was something else that they wanted in their petri dishes
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that we were just not giving them.
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So by combining measurements from many different places
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around the world,
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my colleagues at the University of Southern California,
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Doug LaRowe and Jan Amend,
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were able to calculate that each one of these deep-sea microbial cells
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requires only one zeptowatt of power,
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and before you get your phones out, a zepto is 10 to the minus 21,
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because I know I would want to look that up.
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Humans, on the other hand,
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require about 100 watts of power.
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So 100 watts is basically if you take a pineapple
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and drop it from about waist height to the ground 881,632 times a day.
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If you did that and then linked it up to a turbine,
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that would create enough power to make me happen for a day.
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A zeptowatt, if you put it in similar terms,
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is if you take just one grain of salt
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and then you imagine a tiny, tiny, little ball
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that is one thousandth of the mass of that one grain of salt
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and then you drop it one nanometer,
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which is a hundred times smaller than the wavelength of visible light,
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once per day.
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That's all it takes to make these microbes live.
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That's less energy than we ever thought would be capable of supporting life,
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but somehow, amazingly, beautifully,
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it's enough.
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So if these deep-subsurface microbes
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have a very different relationship with energy than we previously thought,
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then it follows that they'll have to have
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a different relationship with time as well,
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because when you live on such tiny energy gradients,
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rapid growth is impossible.
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If these things wanted to colonize our throats and make us sick,
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they would get muscled out by fast-growing streptococcus
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before they could even initiate cell division.
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So that's why we never find them in our throats.
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Perhaps the fact that the deep subsurface is so boring
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is actually an asset to these microbes.
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They never get washed out by a storm.
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They never get overgrown by weeds.
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All they have to do is exist.
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Maybe that thing that we were missing in our petri dishes
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was not food at all.
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Maybe it wasn't a chemical.
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Maybe the thing that they really want,
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the nutrient that they want, is time.
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But time is the one thing that I'll never be able to give them.
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So even if I have a cell culture that I pass to my PhD students,
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who pass it to their PhD students, and so on,
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we'd have to do that for thousands of years
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in order to mimic the exact conditions of the deep subsurface,
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all without growing any contaminants.
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It's just not possible.
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But maybe in a way we already have grown them in our petri dishes.
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Maybe they looked at all that food we offered them and said,
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"Thanks, I'm going to speed up so much
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that I'm going to make a new cell next century.
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Ugh.
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(Laughter)
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So why is it that the rest of biology moves so fast?
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Why does a cell die after a day
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and a human dies after only a hundred years?
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These seem like really arbitrarily short limits
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when you think about the total amount of time in the universe.
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But these are not arbitrary limits.
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They're dictated by one simple thing,
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and that thing is the Sun.
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Once life figured out how to harness the energy of the Sun
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through photosynthesis,
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we all had to speed up and get on day and night cycles.
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In that way, the Sun gave us both a reason to be fast
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and the fuel to do it.
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You can view most of life on Earth like a circulatory system,
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and the Sun is our beating heart.
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But the deep subsurface is like a circulatory system
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that's completely disconnected from the Sun.
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It's instead being driven by long, slow geological rhythms.
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There's currently no theoretical limit on the lifespan of one single cell.
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As long as there is at least a tiny energy gradient to exploit,
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theoretically, a single cell could live
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for hundreds of thousands of years or more,
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simply by replacing broken parts over time.
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To ask a microbe that lives like that to grow in our petri dishes
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is to ask them to adapt to our frenetic, Sun-centric, fast way of living,
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and maybe they've got better things to do than that.
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(Laughter)
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Imagine if we could figure out how they managed to do this.
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What if it involves some cool, ultra-stable compounds
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that we could use to increase the shelf life
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in biomedical or industrial applications?
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Or maybe if we figure out the mechanism that they use
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to grow so extraordinarily slowly,
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we could mimic it in cancer cells and slow runaway cell division.
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I don't know.
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I mean, honestly, that is all speculation,
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but the only thing I know for certain
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is that there are a hundred billion billion billlion
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living microbial cells
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underlying all the world's oceans.
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That's 200 times more than the total biomass of humans on this planet.
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And those microbes have a fundamentally different relationship
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with time and energy than we do.
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What seems like a day to them
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might be a thousand years to us.
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They don't care about the Sun,
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and they don't care about growing fast,
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and they probably don't give a damn about my petri dishes ...
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(Laughter)
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but if we can continue to find creative ways to study them,
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then maybe we'll finally figure out what life, all of life, is like on Earth.
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Thank you.
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(Applause)
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