Astrobiology is becoming an increasingly discussed topic as new exoplanets are being found and we discover more about the worlds of our own solar system. Of course, for there to be life on other planets, it first needs to come into existence on its own through abiogenesis, or the creation of life through non-biological sources. Perhaps our best way to learn about how abiogenesis might occur on other worlds is to consider how it occurred on ours. While we can never be entirely sure as to the causes of life on Earth, one of the leading candidates for the catalyst behind abiogenesis is the humble hydrothermal vent.
Hydrothermal vents are the result of water underneath the seafloor being heated by the mantle and erupting out of the ground in sustained streams, sometimes at temperatures of over 300 degrees Celsius (although the water is still liquid due to the extreme pressures of the deep ocean). At the depths that they are found, no sunlight at all reaches the seabed, so you might think hydrothermal vents would be barren of life…
Hydrothermal vents actually have many times the biological density of the surrounding seafloor, primarily due to extremophile bacteria which get their energy by processing chemicals in the hydrothermal vent fluid. This is significant because these bacteria due not rely on the sun for energy, even indirectly (unlike most other deep-sea creatures, which feed on detritus further up in the water column). And because they are in the deep sea, they are shielded from events which occur further up, such as asteroid impacts or extreme solar radiation. This makes hydrothermal vents, which would have been much more common in Earth’s early life due to increased geological activity, ideal places for life to develop, providing a safe harbour from the outside chaos. Besides this, there are many chemicals present in hydrothermal vent fluid important for biological activity that were not present in the ancient atmosphere, such as methane and ammonia. Finally, the oldest known life that has been discovered are bacteria fossilized in hydrothermal vent chimneys, and this life appeared almost as soon as the Earth’s surface had cooler sufficiently to support an ocean.
This all goes to show that other worlds, which have surface conditions very averse to life, may still be able to harbour it. Take Europa, whose surface is extremely cold and which has virtually no atmosphere. Any yet, it is known to be geologically active, with a subsurface ocean. So it is very possible that Europa is home to hydrothermal vents and if this is the case, it may present
the very same conditions that spawned life on Earth.