Nick Lane
Life is a side reaction of a main energy-releasing reaction. That remains the case today, after 4 billion years of evolutionary refinement. If modern cells produce 40 times more waste than organic matter, just think how much the first primitive cells, without any enzymes, would have had to make! Enzymes speed up chemical reactions by millions of times the unconstrained rate. Take away those enzymes, and throughput would need to increase by a similar factor, say a millionfold, to achieve the same thing. The first cells may have needed to produce 40 tonnes of waste – literally a truck-load – to make 1 gram of cell! In terms of energy flow, that dwarfs
even a river in spate; it’s more like a tsunami.
The sheer scale of this energetic demand has connotations for all aspects of the origin of life, yet is rarely considered explicitly. As an experimental discipline, the origin-of-life field dates back to 1953 and the famous Miller–Urey experiment, published in the same year as Watson and Crick’s doublehelix paper. Both papers have hung over the field ever since, casting a shadow like the wings of two giant bats, in some respects rightly, in others regrettably. The Miller–Urey experiment, brilliant as it was, bolstered the conception of a primordial soup, which in my view has blinkered the field for two generations. Crick and Watson ushered in the hegemony of DNA and information, which is plainly of vital importance to the origin of life; but considering replication and the origins of natural selection in near isolation has distracted attention from the importance of other factors, notably energy.
The vital question page 67
How could a cell be built from scratch? There must be a continuously high flux of reactive carbon and usable chemical energy, flowing past rudimentary catalysts that convert a modest proportion of that flux into new organics. This continuous flux must be constrained in some way that enables the accumulation of high concentrations of organics, including fatty acids, amino acids and nucleotides, without compromising the outflow of waste. Such a focusing of flow could be achieved by a natural channelling or compartmentalisation, which has the same effect as the channelling of flow in a water mill – it increases the force of a given flux in the absence of enzymes, so lowering the total amount of carbon and energy required. Only if the synthesis of new organics exceeds their rate of loss into the outside world, enabling their concentration, will they self-assemble into structures such as cell-like vesicles, RNA and proteins Plainly this is no more than the beginnings of a cell – necessary, but far from sufficient. But let’s put aside the details for now, and focus on just this one point. Without a high flux of carbon and energy that is physically channelled over inorganic catalysts, there is no possibility of evolving cells. I would rate this as a necessity anywhere in the universe: given the requirement for carbon chemistry, thermodynamics dictates a continuous flow of carbon and energy over natural catalysts. Discounting special pleading, that rules out almost all environments that have been touted as possible settings for the origin of life: warm ponds (sadly Darwin was wrong on that), primordial soup, microporous pumice stones, beaches, panspermia, you name it. But it does not rule out hydrothermal vents; on the contrary, it rules them in. Hydrothermal vents are exactly the kind of dissipative structures that we seek – continuous flow, far-from-equilibrium electrochemical reactors
Unlike black smokers, alkaline vents have nothing to do with magma, and so are not found directly above the magma chambers at the spreading centres, but typically some miles away. They are not superheated, but warm, with temperatures of 60 to 90°C. They are not open chimneys, venting directly into the sea, but riddled with a labyrinth of interconnected micropores. And they are not acidic, but strongly alkaline. Or at least, these are the properties that Russell predicted in the early 1990s on the basis of his theory. His was a lone and impassioned voice at conferences, arguing that scientists were mesmerised by the dramatic vigour of black smokers, and overlooking the quieter virtues of alkaline vents. Not until the discovery of the first known submarine alkaline vent in the year 2000, dubbed Lost City, did researchers really begin to listen. Lost City, remarkably, conforms to almost all of Russell’s predictions, right down to its location, some 10 miles from the mid-Atlantic Ridge. As it happens, this was the time that I first began thinking and writing about bioenergetics in relation to the origins of life (my book Oxygen was published in 2002). These ideas were immediately appealing: for me, the wonderful reach of Russell’s hypothesis is that, uniquely, it ties in natural proton gradients to the origin of life. The question is: how, exactly?
Life is a side reaction of a main energy-releasing reaction. That remains the case today, after 4 billion years of evolutionary refinement. If modern cells produce 40 times more waste than organic matter, just think how much the first primitive cells, without any enzymes, would have had to make! Enzymes speed up chemical reactions by millions of times the unconstrained rate. Take away those enzymes, and throughput would need to increase by a similar factor, say a millionfold, to achieve the same thing. The first cells may have needed to produce 40 tonnes of waste – literally a truck-load – to make 1 gram of cell! In terms of energy flow, that dwarfs
even a river in spate; it’s more like a tsunami.
The sheer scale of this energetic demand has connotations for all aspects of the origin of life, yet is rarely considered explicitly. As an experimental discipline, the origin-of-life field dates back to 1953 and the famous Miller–Urey experiment, published in the same year as Watson and Crick’s doublehelix paper. Both papers have hung over the field ever since, casting a shadow like the wings of two giant bats, in some respects rightly, in others regrettably. The Miller–Urey experiment, brilliant as it was, bolstered the conception of a primordial soup, which in my view has blinkered the field for two generations. Crick and Watson ushered in the hegemony of DNA and information, which is plainly of vital importance to the origin of life; but considering replication and the origins of natural selection in near isolation has distracted attention from the importance of other factors, notably energy.
The vital question page 67
How could a cell be built from scratch? There must be a continuously high flux of reactive carbon and usable chemical energy, flowing past rudimentary catalysts that convert a modest proportion of that flux into new organics. This continuous flux must be constrained in some way that enables the accumulation of high concentrations of organics, including fatty acids, amino acids and nucleotides, without compromising the outflow of waste. Such a focusing of flow could be achieved by a natural channelling or compartmentalisation, which has the same effect as the channelling of flow in a water mill – it increases the force of a given flux in the absence of enzymes, so lowering the total amount of carbon and energy required. Only if the synthesis of new organics exceeds their rate of loss into the outside world, enabling their concentration, will they self-assemble into structures such as cell-like vesicles, RNA and proteins Plainly this is no more than the beginnings of a cell – necessary, but far from sufficient. But let’s put aside the details for now, and focus on just this one point. Without a high flux of carbon and energy that is physically channelled over inorganic catalysts, there is no possibility of evolving cells. I would rate this as a necessity anywhere in the universe: given the requirement for carbon chemistry, thermodynamics dictates a continuous flow of carbon and energy over natural catalysts. Discounting special pleading, that rules out almost all environments that have been touted as possible settings for the origin of life: warm ponds (sadly Darwin was wrong on that), primordial soup, microporous pumice stones, beaches, panspermia, you name it. But it does not rule out hydrothermal vents; on the contrary, it rules them in. Hydrothermal vents are exactly the kind of dissipative structures that we seek – continuous flow, far-from-equilibrium electrochemical reactors
Unlike black smokers, alkaline vents have nothing to do with magma, and so are not found directly above the magma chambers at the spreading centres, but typically some miles away. They are not superheated, but warm, with temperatures of 60 to 90°C. They are not open chimneys, venting directly into the sea, but riddled with a labyrinth of interconnected micropores. And they are not acidic, but strongly alkaline. Or at least, these are the properties that Russell predicted in the early 1990s on the basis of his theory. His was a lone and impassioned voice at conferences, arguing that scientists were mesmerised by the dramatic vigour of black smokers, and overlooking the quieter virtues of alkaline vents. Not until the discovery of the first known submarine alkaline vent in the year 2000, dubbed Lost City, did researchers really begin to listen. Lost City, remarkably, conforms to almost all of Russell’s predictions, right down to its location, some 10 miles from the mid-Atlantic Ridge. As it happens, this was the time that I first began thinking and writing about bioenergetics in relation to the origins of life (my book Oxygen was published in 2002). These ideas were immediately appealing: for me, the wonderful reach of Russell’s hypothesis is that, uniquely, it ties in natural proton gradients to the origin of life. The question is: how, exactly?
