How Five Elements Define Life On Earth

IRA FLATOW: This is Science Friday. I’m Ira Flatow.

When science fiction writers describe life on our planet, they often say we’re all carbon-based life forms. And when looking for life in our solar system, NASA’s guiding principle is follow the water– H2O. Why is that?

Well, when you look at what’s in our cells, over 99% is made up of those three elements– carbon, hydrogen, and oxygen. Plus, there are two more– nitrogen and phosphorus.

In his new book, Elemental: How Five Elements Changed Earth’s Past and Will Shape Our Future, Stephen Porder writes about how these five elements– what he calls life’s formula– tell the story of life on our planet, from cyanobacteria to human civilization to climate change. He’s associate provost for sustainability and professor of ecology, evolution, and organismal biology at Brown University, in Providence, Rhode Island.

Stephen, welcome to Science Friday.

STEPHEN PORDER: Oh, it’s so great to be here. Thanks for having me.

IRA FLATOW: I get the impression from reading your book that you felt a real need to write this book. Is that right?

STEPHEN PORDER: I really did. And the reason that I did was that we are in the middle of really existential environmental anxiety. And sometimes it feels like what we’re doing is so bizarre and abnormal and impossible to solve that it engenders despair. And I think, actually, that what we can learn from the commonalities we have with other organisms that have changed the world can help us think clearly and shape a more sustainable future.

And so I thought looking back at the past and thinking about how that would allow us to move forward in a productive way would be a message that we might need right now.

IRA FLATOW: OK. Let’s look back at the past, then. Life doesn’t all use these elements in the same way, right? What’s useful to one might be detrimental to another.

STEPHEN PORDER: Yes. But I think what you said at the beginning is also really important. We’re all made of the same stuff.

IRA FLATOW: Right.

STEPHEN PORDER: And so that, in itself, is kind of an interesting story. But the other part of it is that four of those elements you mentioned– so hydrogen, oxygen, carbon, and nitrogen– play a really critical role in determining the climate and environmental conditions on the planet.

And so when organisms evolve a new way of getting these elements, they have the capacity to change the world. And it’s really unusual for that to happen. But when it does happen, really big changes can occur.

So the cyanobacteria– this is a story that is deep in the Earth’s past– so 2.5 billion years ago, which is about halfway through Earth’s history– and these organisms figure out evolutionarily a way to get better access to carbon. They evolve a new way of doing photosynthesis that is much more efficient. So they get this great energy source. They use the sunlight more efficiently.

And they also evolve a way to get access to nitrogen, which allows them to build more machinery to capture even more sunlight. And together, those two processes allow them to wildly proliferate across the planet.

But as a byproduct of their chemistry, they spill a pollutant out into the atmosphere. And that pollutant is oxygen. The oxygen that we breathe, that all multicellular life depends on, it wouldn’t be here if it weren’t for the cyanobacteria accidentally polluting the planet.

They probably caused the biggest environmental change of all time. And that set the stage for the evolution of all the organisms that you and I interact with on a daily basis. So it was an unintended consequence of their innovation. And although in the long run it’s certainly good for humans that they did it, at the time it was an enormous environmental catastrophe.

IRA FLATOW: Wait– what do you mean it was an environmental catastrophe?

STEPHEN PORDER: Yeah. So to dive into that we need to understand a little bit about what Earth was like at that time. So because there was no oxygen in the air, the greenhouse blanket that was keeping the Earth warm was actually composed mostly of methane. So methane is a really strong greenhouse gas. And that’s actually the only thing that was keeping Earth unfrozen because the sun was quite a bit fainter during early Earth.

So you have this very strong greenhouse blanket, keeping the Earth unfrozen. And life is going along and there’s no dissolved oxygen in the water and there’s no oxygen in the air. And then cyanobacteria come along. And they’re so successful that they pump enough oxygen into the air that two things happen. One, all the organisms that are used to there being no oxygen around are all of a sudden faced with competition from organisms that are using oxygen.

And two, the oxygen bubbles out of the oceans and reacts with all that methane that was keeping the planet unfrozen. And we actually precipitate a global, we think, glaciation. Because the waste product of the cyanobacteria changes the global greenhouse. So it’s unintended catastrophe that follows this wild proliferation and evolutionary success, for lack of a better word.

IRA FLATOW: Stephen, we’ve all heard about snowball Earth, where the Earth was covered in all these glaciers. But you say there have been many incidences of snowball Earth having to do with plants. Tell me about that.

STEPHEN PORDER: Yeah. So you’re right– there have been a series of events, where the Earth has frozen either partially or completely. The first one we know of was created by the cyanobacteria that we already talked about. There was another one in between the cyanobacteria and the story of the land plants. But land plants evolve into a world that’s almost entirely tropical. You could have swum at the North Pole in a bathing suit without a wet suit.

And they spread across this tropical world and build the world’s first tropical forests all across the continents. And then, over the course of about 100 million years, they pull so much carbon dioxide out of the air– the carbon dioxide that was keeping the planet warm at the time– that they actually changed the climate enough that those first tropical forests disappear.

And it is in fact, the remnants of some of those tropical forests that humans find as coal deposits 300 million years later, dig up, and begin to burn.

IRA FLATOW: All right. Let’s talk about red rocks. You see them everywhere. Tell us about what you can tell from red rocks.

STEPHEN PORDER: Yeah, I love this story because it’s a very personal story for me. One of the things that I love about science is that it teaches you a new way to see the world and to see things you never noticed before.

And when I was in college, I took this geology class. I was in I went to college in Western Massachusetts. And they started talking about all these red rocks that were surrounding us. And I had never noticed that rocks really were different colors or never thought that there might be a reason for them being different colors. And all of a sudden this world opened up to me of like, oh, yeah, all these rocks are red.

And the professor was trying to teach us something really profound, which I completely missed as an undergrad. Which is that, for the first 2 billion years of Earth history, there really weren’t any red rocks. And those red rocks appear because the cyanobacteria oxygenated the planet.

That red is actually just rust. It’s rusted iron. But you can’t rust iron if there’s no oxygen. And so the first red rocks really appear in the sedimentary rock record when the planet begins to oxygenate.

And so there’s periodic episodes before that, but you really don’t see prolific red rocks until this period. So the red color is actually indicative of this enormous Earth-changing event called the Great Oxidation Event. To me, it’s just a really great window into how learning something new allows you to see something about the world that you just never thought about before.

IRA FLATOW: Well, let’s talk about the rest of what’s going on because we’re talking a lot about oxygen. But I don’t really think that much about phosphorus. And you showed me how important it was in your book about plants can’t grow without it, right?

STEPHEN PORDER: Well, yeah, none of us can grow without it. Phosphorus is one of the five elements that we talk about in the book. And it’s sort of the oddball one. And in some ways, it’s the most important. Phosphorus is a key atom in pretty much every biological molecule you’ve ever heard of. If you’ve heard of ATP, which is the energy source for cells, the “P” is phosphorus.

And so we can’t live without it. Nothing can live without it. And unlike carbon, which is in the air and in the rocks and dissolved in water– and obviously H2O, the oceans are made of that– and nitrogen, which makes up 80% of the air, phosphorus only exists in rocks. It doesn’t have a gas form. It doesn’t dissolve super well in water.

And so if you’re living in the ocean, for example, how do you get your phosphorus? You’re nowhere near rocks. You’re floating in the middle of the Pacific Ocean, for example. The rocks are way down below you or they’re all the way on the continents. And so the only way you get it is by this trickle of dust that’s blowing off the continents or maybe flowing in from rivers.

And so we think that phosphorus and other elements that are only found in rocks are profoundly limiting to life in the ocean. And so the next big environmental change that I talk about is when organisms– actually plants– make their way out of the oceans. And this is very recent in geologic time, but it’s still a long time ago– so about 400 million years ago. So million, not billion.

Plants evolve onto the continents. And they get access to all of this phosphorus that was so limiting in the ocean because they’re growing right on top of the rocks. And they become and still are the world’s best miners.

So they evolve all these strategies to live on land. And living on land is tough, right? Because it’s harder to get water. And so that’s a real challenge. But if you can solve that challenge by evolving roots and partnerships with fungi that help you gather water from the soil, then you have a couple of really big advantages.

One, you can capture all this sunlight that was hitting the continents and nobody was using. So it’s like an extra energy source again. But also you get access to phosphorus and the other elements that come from rocks because you’re sitting right on top of them, dissolving them with your roots.

And so plants, like the cyanobacteria before them, innovate this incredible evolutionary step of being able to move to a new place and capture all this new energy and also get access to phosphorus. And that really allows them to take over the continents.

IRA FLATOW: Wow. What a story. And then there’s another huge environmental change– our air is largely nitrogen, but finding ways to make use of that nitrogen was a very big step, right, both for early life forms and later for humans?

STEPHEN PORDER: Yeah. So I mentioned in the cyanobacteria part of the story that they evolved a way to pull nitrogen out of the air. And the key here is that nitrogen in the air, it’s super abundant– about 80% of all atoms in the air are nitrogen– but they’re stuck to each other– two nitrogen atoms stuck to each other– in a way that makes them pretty much unusable. So you and I breathe that nitrogen in with every breath and it just goes right back out unaltered.

There are some cyanobacteria– and other bacteria– that evolved this biological machine that could split those two nitrogen atoms apart and turn them into a useful form. But it wasn’t actually until humans that any multicellular organism cracked that problem. And so in the early 20th century, Fritz Haber, who won the Nobel Prize for this, figured out a benchtop process that could do it, and then Carl Bosch industrialized that process.

And the so-called Haber-Bosch process is how we make all of our nitrogen fertilizer. And that is a energy-intensive fossil fuel-dependent process, but it’s the only way we could feed the number of people we have on the planet.

So this is a revolution 4 billion years in the making. We become the first multicellular organism that is able to capture nitrogen from the air and turn it into a useful product.

IRA FLATOW: This is Science Friday, from WNYC Studios.

Of these five elements you talk about, is there one more important than the others?

STEPHEN PORDER: No. Because you can’t live without any of them.

IRA FLATOW: Yeah, that would make them important.

STEPHEN PORDER: Yeah. And what’s interesting is that, if you look at the chemistry of a human being and you look at the chemistry of a bacterium, there’s a lot of differences between us obviously. But actually we are all hydrogen, oxygen, carbon, nitrogen, and phosphorus in roughly the same amounts in that order of abundance.

And so sometimes when I give talks about this stuff I say, what is life? That’s a very big, deep, philosophical, spiritual question. What is life? Well, life is lots of things. But from the perspective of our chemistry, life is a constant struggle to gather these five elements from our surroundings. And that’s true for humans and fungi and bacteria and plants and elephants and every other living thing.

So there isn’t one that’s more important than the other because no life at all could exist without all five.

IRA FLATOW: Right. You make a really interesting point in your book, which I have come across in various ways as a student, as someone who talks about science education. And you write about how many people don’t recognize the interplay of these elements in all things because science is often taught in silos, as separate disciplines.

STEPHEN PORDER: Yeah, it’s quite remarkable to me. I’ve taken a lot of science in high school and in college and even a master’s degree before I got my PhD, and I never really understood that our living planet is not just a living planet because it houses life, but because it’s shaped by life. And this interaction between the living and unliving world is really what determines the characteristics both of our planet and the organisms that live upon it.

And the siloed way we teach biology is that you study DNA, and you’re never told that DNA has a lot of carbon and nitrogen and phosphorus in it. And then you study chemistry, and you learn about oxidation and reduction reactions. And you never learn that life itself is one giant oxidation reduction reaction. And then you take geology. And you might learn about glaciations or climate change, but you don’t understand that organisms play a really big role in shaping our climate.

So we just don’t teach it that way and we don’t think about it that way, but it’s an incredibly powerful way to visualize the world. And I think, importantly– and one of the things I really try and highlight in the book– is that this framework allows us to think about our current climate and sustainability challenges and envision a path forward. And that’s really, I think, a key message that I want to get out there.

IRA FLATOW: Tell me more about that key message.

STEPHEN PORDER: So world-changing organisms like humans and cyanobacteria and land plants share a lot in common, as we’ve talked about. They share these elements and they also share innovations in gathering these elements in radical new ways. In the case of the cyanobacteria and plants, it was evolutionary. In the case of humans, it’s our ingenuity, which I suppose is evolutionary in terms of we evolved big brains that work in a particular way.

But the challenges that we face– climate change, feeding a growing population without destroying the ecosystems upon which we all depend– those grand challenges are rooted in these elements. So we burn fossil fuels for energy, and that powers all of our society. But we actually have one key difference from our world-changing predecessors. We don’t need to emit a waste byproduct the way they did. We don’t need to be emitting carbon dioxide in order to get the energy that we need.

Only about 2%– maybe 1%– of the energy we need is to fuel our own bodies. The rest is to power the rest of society– the lights, the transportation, the heating, all that stuff. So we are decoupled in a way from the fundamental constraints that the cyanobacteria and plants had. We can see it better way forward.

Similarly, we can be wiser in the way that we use these other critical elements– nitrogen, phosphorus, and water– and in so doing, avoid the consequences– the sort of unintended environmental consequences– that our world-changing predecessors had no way to avoid.

So I really believe that a more sustainable society is built on the wise management of these five elements. That doesn’t mean that that’s all it will require to have a sustainable society. But it’s necessary, if not sufficient. And so I believe that it’s a really good starting point.

IRA FLATOW: Stephen Porder, thank you for taking time to be with us today.

STEPHEN PORDER: Thank you so much for having me. It was super fun. I appreciate the opportunity.

IRA FLATOW: Stephen Porder is author of the book, Elemental: How Five Elements Changed Earth’s Past and Will Shape Our Future, and is associate provost for sustainability and Professor of ecology, evolution, and organismal biology at Brown University.

You can read an excerpt from the book on our website. It’s up there at sciencefriday.com/elemental.

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