Searching for Life Where the Sun Donít Shine (part 3): Explorations to the Seafloors of Earth and Europa
But how could such an alien process — fundamentally different from the basis for the vast majority of all life on Earth — exist here?
Enter Günter Wächtershäuser. A German chemist turned patent lawyer who specializes in chemical and biochemical inventions, Wächtershäuser (pronounced VEK-terz-hoi-zer) first proposed in 1988 that a similar chemosynthetic process to the one observed on the Galapagos Hydrothermal Vent Expedition had been around on Earth for a very long time. Not only was it common to the planet Earth throughout its history, he argues, this process was fundamental to all living ecosystems going back to the very first genesis of life around four billion years ago.
If we could travel back to that time, we’d see a wholly different Earth than we see today. We’d see a planet emerging from the cataclysm of an impact with a rogue planet that created the Moon and is thought to have tilted the Earth’s axis to about 23.5 degrees. The planet would have only recently cooled down enough to bear a solid crust, though intense volcanism and geological upheaval would have created a toxic atmosphere almost completely devoid of oxygen. With no ozone layer, the planet would be drenched with massive doses of ultraviolet light and radiation from the Sun. We’d see comets, meteorites and asteroids raining down across the landscape in a period of heavy bombardment, leaving behind condensed water that would form clouds and eventually, combined with volcanic outgassing, oceans. Photosynthesis wouldn’t take place on Earth for perhaps another two billion years. Yet, it would have been in this literal hell on Earth where we would have seen (if we’d remembered to take a microscope with us) the first life forms start to appear.
This coupling between the catalyst and the product of an organic reaction is the key first step of Wächtershäuser’s theory.
What comes next is the miracle of evolution. Starting with these metals and gases reacting together as life emerged, Wächtershäuser says evolution starts with the beginning of a primitive metabolism that created increasingly complex chemical reactions, eventually leading over time to the formation of DNA — life’s blueprints for making more living cells today. Before living cells were around, these metals and gases reacted together in a purely chemical sense, according to predetermined “pathways.” There were only so many compounds around back then and only so many ways these could react together.
“Hydrogen sulfide, sulfur dioxide. Hydrogen cyanide, carbon monoxide, carbon dioxide, hydrogen, nitrogen, ammonia,” says Wächtershäuser, pausing before adding “Oh, phosphorus oxide, P4O10. That’s it.”
Aside from a few other trace molecules, these were the gases belched from the belly of the planet that formed the first chemical reactions that served as the precursor to life.
When these gases come up from deep within the Earth, they move from a state of high pressure, high temperature to one of low pressure, low temperature. This happens rapidly, causing a non-equilibrium condition called quenching—where the ratio of gases at a high temperature gets frozen in the same concentration upon transferring into a low temperature environment.
The quenching is important because it creates a chemical potential. The chemical potential drives the reactions between gases and metals at hydrothermal vents. Here, because of the unique combination of the right gases and the right metals at the right temperatures, reactions start to build off each other, creating “a synthetic reaction whereby the organic products that are synthesized promote in turn the rate of another reaction,” says Wächtershäuser.
In other words, certain reactions create byproducts that then are used to speed up other reactions, leading to longer, more complex strings of organic molecules.
According to his theory, all evolution happens using this method of “feed forward” reactions, where organic products promote other reactions yielding new organic products of increasing complexity. This is what gave rise to amino acids, peptides, sugars, proteins, nucleotides, and nucleic acids, like DNA and RNA. After that, as the theory goes, life evolved higher levels of complexity and ventured beyond vent communities. It isn’t clear when photosynthesis first arose, but most estimates range from 2.5 to 3 billion years ago. The rest, as they say, is history.
Since we can’t go back in time, we’ll never know if Günter’s theory of life rising from the depths of the Earth’s molten innards is true or not. And his is only one of several competing origin of life theories, which generally fall into two camps. Metabolism-first theories (like the Iron-Sulfur World Theory) start with simple molecules that build increasing levels of complexity. Replicator-first theories, on the other hand, suggest that simple organic molecules occur naturally and are able to self-replicate right from the start.
Chemist Stanley Miller is in the replicator-first camp. Miller, who is sometimes referred to as the “Father of ‘origin of life’ chemistry,” earned early fame for a classic experiment he conducted in 1952 as a graduate student with Harold Urey demonstrating how amino acids could be generated in a lab environment from simple compounds subjected to electrical discharges in the early Earth atmosphere. The spontaneous creation of amino acids doesn’t by itself explain life’s origins, since it’s still a huge jump to go from simple amino acids to complex, self-replicating chains of genetic instructions contained within DNA and RNA. But his findings did lay the cornerstone for origin of life research and sparked many curious minds to test all sorts of combinations of conditions that could have been around on the early Earth. Still, sixty years later, none of these efforts have been able to replicate life from scratch in a lab.
But Wächtershäuser thinks it’s too much of a jump to assume life began with the ability to self-replicate. “The beginning of the genetic machinery is not replication. Replication has no purpose in itself,” says Wächtershäuser.
To him, the beginning of the genetic machinery of replication begins with something akin to the chemistry that goes on in the core of the ribosome, which is a bit like the manufacturing plant of all cells. That chemistry boils down to peptide formation—basically, simple amino acids linked together. It’s a crucial step and it’s something his experiments have been able to produce in the lab under high temperature conditions—the same conditions that are thought to have been around in the early Earth around hydrothermal vent systems. It isn’t conclusive proof his theory is right, but he’s getting closer.
Unfortunately for Wächtershäuser, maybe the best proof to his theory lies about 500 million miles away from his lab in Germany, beneath the icy shell of a moon discovered more than 400 years ago by a man named Galileo Galilei: Jupiter’s moon Europa.