Everything We Think We Know About The Origin Of Life On Earth Could Be Wrong
We began in the deep sea, says Nick Lane – and it's probably the same on other planets.
For a model of the dawn of life on Earth, it doesn't look like much. I'm in a lab in the University College London (UCL) biology department, staring at something that will, it is hoped, one day demonstrate how the whole business of cells and reproduction and everything really kicked off. It's basically a glass cabinet with two smaller glass cylinders inside it, linked with plastic tubing. Something inside is apparently held together with tinfoil. Is that special scientific tinfoil, I ask. "No," says Nick Lane, cheerfully. "It's just tinfoil. I told you it was humble."
It's humble in appearance – humble in design and construction, too – but not humble in ambition. The little tinfoil contraption is a simulation of a sort of deep-sea vent, a place where warm, mineral-rich water flows out into the oceans. The sort of place where, Lane thinks, life on Earth must have begun. More than that, he thinks that it is a clue to how life will be throughout the universe.
There's a problem at the heart of biology. It is: No one knows why all complex life is so similar. The history of life on Earth used to look fairly straightforward, but in the last few decades, it's become obvious that something very weird is going on, and it's not clear why. Lane, a professor of evolutionary biochemistry at UCL and author of a new book called The Vital Question, thinks he has the answer.
A big, bearded, rather handsome northerner in his late forties who looks more like a rugby player than a scientist, Lane meets me in his office on the second floor of the appropriately named Darwin Building. Until recently, he says, "There didn't really seem to be a problem to be explained," because we thought we knew the bare bones of the story. "It only became evident recently that there is this very strange history of life on Earth."
The textbook history of life on Earth goes something like this. About 4 billion years ago, the first life arose. Exactly what and where it was, we didn't know, but quickly the first bacteria evolved. They took over the planet, and remained the only type of life for billions of years. But then they evolved photosynthesis – the ability to use sunlight as energy. Photosynthesis creates oxygen gas, and so, about 2 billion years ago, the atmosphere suddenly became rich in oxygen. Oxygen is toxic, so a lot of the bacteria died, but some others managed to harness it, and the extra energy meant that they could evolve into ever more complex forms. But, says Lane, this almost certainly isn't true. And the reason it almost certainly isn't true is because we are so like mushrooms.
Under a microscope, the cells of a mushroom and a human being – or an oak tree or a leopard or a stag beetle – are remarkably similar. "You can list off, depending on how finely you want to grade it, hundreds and hundreds of shared features, right down to the positions of non-coding sequences in genes," says Lane.
"You think of evolution as being adaptation to a particular lifestyle, to a particular set of circumstances," he continues. "But a mushroom and a human being have completely different sets of circumstances, and yet our cells are exactly the same, give or take. Why is that?"
If a burst of oxygen into the atmosphere suddenly allowed life to explode into all the complex forms you see in the world, says Lane, then you'd expect to see lots of different kinds of complex life springing up all over the place, taking advantage of this new source of energy. But instead, it looks very much like all complex life – everything from amoebae to elephants – comes from one common ancestor. "There's this weird single origin of all complex life, all of which has these strikingly complex traits which we all share, you and me and the fungus," says Lane.
The origin happened something like this. Until about 2 billion years ago, there were only two simple forms of life: bacteria and archaea. And somehow, a group of bacteria managed to get inside a group of archaea. "A population of archaea would have been living the ocean, and they'd have had a population of bacteria which are living alongside them," says Lane. "They've got some sort of a metabolic exchange going on, so one is living off the waste product of the other or something like that. They snuggle up to each other to get maximum exposure to it, and some end up getting inside."
And once inside, the bacteria weren't eaten, and they didn't kill or harm their hosts. Instead, the two continued to cooperate. The archaea provided food and shelter for the bacteria, and the waste product of the bacteria acted as a more powerful fuel for the archaea. The symbiosis created new, complex cells called eukaryotes (their forebears, the bacteria and archaea, are called prokaryotes), which proved incredibly successful: All complex life, from hyenas and humans to hydrangeas and hammerhead sharks, descended from those first eukaryotes. And in each of our cells there are tiny descendants of those ancient bacteria called mitochondria, which provide energy for our cells.
That's pretty widely accepted. But the question is: Why is all complex life a result of that one event? Why couldn't bacteria or archaea, at some point in the previous 2 billion years – or since – have evolved to become more complicated?
The answer that Lane gives, if it's correct, has profound implications – for how life began here, and for how it is in the rest of the universe. "The reason complex life is fantastically unlikely is an energetic reason, to do with the way that bacteria produce their energy, which is by this strange mechanism of pumping protons across a membrane," says Lane. Cells generate energy by letting the protons flow back across the membrane, like water through a hydroelectric dam. All life generates its energy the same way.
What that means is that the traditional picture of how life began in the first place – the "primordial soup", or what Darwin called a "warm little pond", full of organic chemicals, being occasionally struck by lightning until a simple replicating molecule arose – doesn't work. Life isn't just information, isn't just DNA. It's also chemistry – or, more accurately, a sort of electricity. There needs to be this flow of protons. For there to be a flow, there needs to be an imbalance. Life needs a proton-rich outside and a proton-starved inside. It needs a cell.
A soup couldn't do it. A soup is uniform; it is stable, and stability is exactly the same as death. But, says Lane, there is one kind of environment where the conditions are perfect for the start of life. And that environment is extraordinary.
Deep underwater, on a mountain range on the bottom of the Atlantic ocean, there is a place known as the "Lost City": a ghostly range of towering spires, some of them 60 metres tall, detailed like a gothic cathedral. It is a deep-sea hydrothermal vent, and the spires are made by warm, alkaline, mineral-rich water flowing out of the bedrock and into the cold oceans. Similar vents exist on sea floors throughout the world, but the Lost City was the first one found, just 15 years ago. Importantly, the way the spires form is in tiny bubbles: little, semi-permeable bubbles, a few millionths of a metre across. Rather like cells, in fact.
"You need quite an exacting set of circumstances for the origin of life," says Lane. "You need some way of continuously producing organic chemicals, continuously providing the energy needed to make them react, continuously concentrating them, continuously venting off waste, and things like that." These alkaline vents neatly fulfil all these requirements. The Lost City – or rather, an equivalent vent, back in the nascent oceans of the young Earth – is the best bet for where life comes from.
That's where it gets really interesting. All the Lost City and its fellows need to exist is water, heat, and a common, marble-like mineral called olivine. "These conditions are really widespread," says Lane. "We know that they have them on Mars – that's probably what the little bits of methane on Mars come from. It's just a reaction between rock and water. Wherever you've got olivine as a mineral and water, you're likely to produce these kinds of vents and these kinds of systems which ought to be conducive to life."
So, according to this hypothesis, life has a good chance of making a start wherever there is a geologically active planet with plenty of water. Lane goes a bit further: He says that if he's right about how life gets its opening, then the life we can expect to find elsewhere will operate on the same lines, with cells and membranes and carbon and proton gradients. Lane looks a bit wary when he says this. "It's very easy to dismiss this kind of argument by saying, 'You don't have any imagination, the universe is infinite and anything could happen; how sad to try to limit life this way with your own feeble imagination,'" he says. "But I think we can ask scientific questions about why life on Earth is the way it is, and ask if it's generalisable, and only to a point does that spoil things. Life as we see it around us is wonderful, and infinite in its variety."
Lane's views aren't mainstream, says Dr Adam Rutherford, a geneticist and the author of Creation: The Origin of Life/The Future of Life. But he's one of the few people asking the right questions. "This field has been stagnant for 100 years, crippled by the warm little pond/primordial soup idea," Rutherford says. "I've given hundreds of lectures on the origin of life, and someone always brings up primordial soup. But it's an idea that cannot be right." Lane's search for a proton-driven model of the origin of life is the only game in town, as far as Rutherford – who declares an interest, as a fan of Lane's ideas – is concerned. "If you're looking for proton gradients, which are what power all life, then these vents are the only place we know of where they occur naturally," he says. "Until 2000 we didn't even know they existed, then the Lost City turned up, and it's exactly what we're looking for. We were looking for the transition from chemistry to biochemistry, and this looks like it.
"I don't know anyone who thinks as clearly on this as Nick, anyone who's asking the right questions. The thing is, as we all know, all models are wrong, but you try to isolate the ones that are useful, the ones that are least wrong, and Nick's are the least wrong."
Dr Lewis Dartnell, an astrobiologist at the University of Leicester involved in the search for life on Mars, agrees: "I know Nick's work well. From what I understand, the alkaline hydrothermal vents are a very promising location from the point of view of the chemistry. A few researchers have been talking about them for a while, and Nick has recently picked up the baton and really run with it.
"The vents would be likely on any wet terrestrial planet – early Mars or Venus as well as primordial Earth, in our solar system, and by extension any terrestrial exoplanets orbiting other stars. The mechanism would also work for icy moons like Europa which don't have a habitable surface, but do offer a rocky crust in contact with seawater. If Nick et al are right, microbial life could be very common in the universe."
Microbial life – simple, one-celled life – is the key term there. As I've described them, Lane's account of how life began only gets us as far as bacteria. If we made it to other planets and learned that the universe was full of life, but life that was little more than pond slime, it'd be – well, not a disappointment, but hardly the take-me-to-your-leader moment we might want out of our first encounter with aliens. And Lane says the birth of complex life – the moment those bacteria first crawled inside their archaeal neighbours – was such an unlikely event that it has apparently only happened once in Earth's 4.5-billion-year history. Life may well be all over the cosmos, but complex life, the sort of thing that we could interact with, might be incredibly rare.
Or it might not. There are hints, says Lane, that this freak occurrence may not have been quite as freak as all that. "There is one thing, one sample that someone found at the bottom of a trench off the coast of Japan, and it's not obviously a eukaryote or a prokaryote. It looks like a eukaryote, but it's so different in so many ways that it looks like something of independent origin." It's far from clear yet, but it might be that complex life isn't – quite – as unlikely as it appears.
Of course, all of this is still a hypothesis – a highly plausible one, which is taking hold on the scientific community, but still just a hypothesis. That's why Lane and his team are trying to recreate the conditions of the early vents in his lab. "We're trying to re-create a few of the key properties, rather than the whole vent," says Lane. "It's a very simple thing; some parts of it work, and some parts of it don't work at all. It's not easy to simulate a hydrothermal vent in the lab. The difficulty is that deep-sea vents have hydrogen at high pressure, and we don't, because it's a glass reactor. We'll need to build a high-pressure version, and dissolve a lot more hydrogen." Won't that probably explode? He chuckles. "Yeah, but we're going to try it anyway."