Deep Sea Vents, The Key to the Biggest Questions in the Universe?
Deep sea vents occur along the intersections of tectonic plates at the bottom of the world’s oceans and function in a manner similar to geysers. Cold sea water seeps into pores in the ocean floor near the vents. When the water approaches the vent, it heats to temperatures of up to 500 oC and shoots out of the vent into surrounding ocean water. In addition to being extraordinarily hot, the water exiting the vents is strongly acidic and contains high levels of substances such as hydrogen sulfide, which are considered to be highly toxic to life on the surface of the Earth.
Almost nothing about the environment near the vents is compatible with our pre-1977 understanding of life on earth. The absence of the sunlight is a big deal. All life on earth, other than at these deep sea vents, is directly dependent on photosynthesis in which plants capture CO2 from the air and convert it to glucose. This plant-based creation of glucose (a sugar) is the base of the food chain. However, despite being devoid of sunlight, exceedingly hot, and highly toxic, the environments around the vents are teeming with life.
So how can this be? It turns out that these ecosystems exist on a food chain which is entirely distinct and separate from the rest of the world. The base of this food chain consists of bacteria which can create sugars through a process called chemosynthesis. In chemosynthesis, the bacteria convert dissolved carbon dioxide, oxygen, and hydrogen sulfide into sugars, sulfur and water. Then somewhat larger animals eat the bacteria, which are further eaten by animals which are larger yet, and so on. Perhaps the most interesting species at the vents is the tube worm, which has neither a mouth nor an anus. It’s entire energy consumption and waste elimination process is carried out symbiotically through bacteria which live within its body. This process is extraordinarily efficient, allowing tube worms to grow at rates approaching six feet per year.
The discovery of the deep sea vent ecosystems presents provocative questions regarding perhaps the two most significant questions of the earth and the universe – how did life start on earth and are we truly alone in the universe?
There are several theories regarding the origin of life on earth. While I am, as long-time readers might expect, tempted to lay out a detailed review of them all, a summary of their common elements will suffice for this column. The early atmosphere on the earth contained gases of water, hydrochloric acid, carbon dioxide, carbon monoxide and nitrogen. These atmospheric gases then reacted to produce some methane, ammonia, and hydrogen cyanide. As the earth cooled, the water molecules condensed to form the oceans and some of the gas molecules from the atmosphere dissolved in the water.
When energy was applied to the mix of molecules listed in the paragraph above, some organic molecules, such as amino acids, which are key “building blocks” of life were formed. Then, through a process which is still strongly debated, these building blocks began to assemble into more and more complex structures and, eventually, into the first life on earth, single-celled bacteria with no nucleus, called stromatolites.
There are several competing theories regarding what form of energy started the process of forming organic molecules on Earth. The most well known, and the one with far and away the best name, is the Primordial Ooze Theory, developed in the 1920s. In this theory, shallow pools of water, with the appropriate gases dissolved in them, formed organic molecules based on the energy input from UV rays from the sun.
A second, and somewhat complementary theory, was added in the 1950s when scientists recreated the conditions of one of these early-earth water pools and subjected them to electric shocks to simulate lightning strikes. They were able, with the analytical methods available at the time, to identify the creation of 5 amino acids. Later analysis of retains from this experiment with more sophisticated methods revealed that, in fact, 23 different types of amino acids had been created.
The most recent, and to my view most compelling, theory, is that life began at the deep sea vents. Bear in mind that when the oceans were first forming they were not so deep at all, allowing life formed at the shallower vents to reach the surface. The sea vents provided a strong, sustained source of energy, as opposed to lightning or even UV rays which are disrupted by cloud cover and night time.
The data and observations from the vents also pose questions about how “easy” or “hard” it is for life to arise from simpler materials. There are many planets and moons in the universe which contain a mixture of gases similar to those present on the young Earth. Intriguingly, fragments of meteors landing on earth have been shown to contain organic molecules indicating that the Earth is not the only body in our solar system to host some Primordial Ooze. If other bodies in the universe have organic molecules, they could also contain life.
Many astronomers are intrigued by the possibility that life may exist on one of Jupiter’s moons, Europa. Europa is entirely covered by a smooth, thick sheet of ice which sits over an ocean of liquid water estimated to be 60 miles thick. Europa’s mantle is believed to experience plate tectonics similar to Earth’s, which would imply that its oceans would have deep sea vents similar to ours.
The discovery of life on Europa would be, to my point of view, the most significant scientific discovery in the history of our species. Most of what we have learned about Europa thus far has come from several NASA craft fly-bys which occurred in the 1970s. Fortunately, the European Space Agency is launching JUICY (Jupiter Icy Moon Explorer, another awesome name) in 2022 scheduled to arrive in the vicinity of Europa by 2030. JUICY won’t be able bore down through the ice but we can expect to learn a lot more about the prospects for life on Europa from the data it gathers. Just stop for a moment and imagine the reaction here on Earth. Now that would be something.
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