One prominent origin-of-life model posits that life began at deep-sea hydrothermal vents, sometimes referred to as “black smokers.” These structures result when superheated water, rich in dissolved minerals including sulfides, pushes through the Earth’s ocean floor to form a sea vent. When the superheated water comes into contact with the cold water surrounding the vent, the metal sulfides precipitate and give the appearance of black smoke emanating from the sea floor. Over time a chimney-like structure forms.
A complex ecosystem is associated with black smokers. Some bacteria and archaea thrive near hydrothermal vents. Since the discovery of these thriving microbial communities, origin-of-life researchers have thought that perhaps life began in similar locales on early Earth. If life can live at hydrothermal vents today, why couldn’t it originate there as well? After all, the microbes thought to be representatives of some of the oldest organisms on Earth are hyperthermophiles and thermophiles, the types of heat-loving organisms found at these vents.
Additionally, laboratory simulation experiments designed to mimic the vents’ chemical and physical conditions have demonstrated that biologically interesting compounds could have been generated in these locales on early Earth. Presumably, these compounds could have formed a complex chemical mix that eventually spawned the first life-forms.
New research, however, seems to snuff out this particular evolutionary scenario.
This work used the typical biochemical makeup of nucleic acids, such as DNA and RNA, and proteins of hyperthermophiles and thermophiles to determine (from an evolutionary standpoint) the identity of the last universal common ancestor. The composition of these important biomolecules serves as a “molecular thermometer” of sorts. For example, hyperthermophiles and thermophiles possess nucleic acids more enriched in guanine and cytosine than those of organisms that live at more moderate temperatures. Likewise, thermophilic proteins are low in certain amino acids.
The researchers concluded that the last universal common ancestor must have lived at moderate temperatures. That is, it wasn’t thermophilic. This finding means, from an evolutionary vantage point, life’s origin most likely did not take place at hydrothermal vents, thus, negating one more naturalistic scenario.
It looks like smokers are more useful to chefs than to origin-of-life researchers.