4 min to read
Down the Hill the Water Flows
A Tale of Life
We just arrived at the seafloor, carried by hydrothermal fluids (where we left off in our previous tale: “A story of a hydrothermal vent”). It is dark and quite cold, but it did not take long to realize that we are not alone, not by any means. Surrounding us, there is a forest. Not the usual green ones we readily think of. This forest grows in the dark, on big and steep mineral cones. This forest, composed of microorganisms, giant crabs, tubeworms and mussels, thrives at 2,000 km depths, and upon it, rains a colorful palette of elements.
Life and hydrothermal systems are tightly connected. They even share a common story. If we go back to the origins, all the way back to the early Earth, hydrothermal systems and life were not seen as two different things; they were one and the same. Studying life inhabiting these systems can help us understand to a deeper level how it operates and how it has been evolving over time. Such fundamental knowledge will allow us to go outside, look at the stars in the dark sky, and wonder:
Is life indeed a singularity, or a field of flowers, flourishing whenever the soil is fertile enough?
Previously, we travelled to the heart of our planet by following the transformation of seawater into hydrothermal fluids. In this journey, we will peel back the layers of life. When we reach the most fundamental layer, what do we find?
We find energy dissipation.
Every living organism needs energy to be able to grow and replicate. That is a fundamental requirement of being alive. However, energy, for the sake of the word, can be a little bit too abstract. What do we mean by energy? Specifically, life harnesses energy by juggling electrons around. An electron juggler, if you fancy. Life uses molecules that want to donate electrons away (electron donors) and couples it to others that really want one (electron acceptors). This movement of electrons dissipates energy, which life can conserve. However, these molecules have different moods. Some are eager to donate or accept electrons right away, while others will only do so under the right conditions, otherwise, they are fine keeping them to themselves. Thus, the likelihood of a molecule to give or receive electrons is called redox potential. For example, hydrogen has a very negative redox potential, meaning that it is desperate to donate an electron, while oxygen has a very positive one, and goes on about trying to get one whenever it can. Despite this, there is another important factor regarding the juggling of electrons, one that life takes very seriously.
If molecules naturally donate and receive electrons spontaneously, then life cannot work with those easily. As Everett Shock once said: “Things that burst into flames are not good to eat.” If something happens very fast and spontaneously, it is quite hard to get a hold of it, right? You can, for example, imagine a waterfall—lots of energy, very quick, yes. However, have you ever seen a watermill in a waterfall?
Now, let’s say that we have a pond of water on top of a hill. We can agree that the water “wants” to flow downhill. What life does is to carve a small opening for it to flow downwards. The flowing water represents electrons. By having regular ponds down the hill and carving small openings in each of those, life can mediate this water flow. By placing water mills along the way and carefully mediating its path, this movement can be conserved into an energy molecule (or an “energy coin” if you wish) called ATP. So, at one of the most fundamental levels, life taps into energy gradients. If you then replace water ponds with molecules, the ponds change –they change a lot– but the basis is always the same: water flowing downhill.
Why are hydrothermal vents important here? Because here the energy gradients occur naturally, and some are found almost identically within life itself. At some point, life seemed to take this blueprint in its early evolution and evolved from within one of these systems. It’s not by mistake that if you look in the right way, you can still see a hydrothermal system occurring within every cell in the form of a chemiosmotic gradient.
An interesting thing to think about too, is that life might have evolved to mediate the flow downhill. In the early history of our planet, there were so many ponds up the hill that one could argue that life was bound to happen, to evolve as a means to bring the water downhill, to break that disequilibrium, that tension, by carving small openings and allowing the energy to dissipate. In this view, life is a necessary consequence, an endpoint of the evolution of a planet. Life, then, is a planetary phenomenon, the fourth geosphere. Chemical gradients are widespread throughout the cosmos. Thus, maybe, if we look for them, we might find life lurking around.
I like to believe that this is the case – the juggler of electrons is everywhere, guiding and mediating the flow of energy across the cosmos.
That is the tale of Life.
