A Warm Little Pond to Hydrothermal Vents

Early Speculations

“But if, (and oh what a big if) we could conceive in some warm little pond with all sorts of ammonia and phosphoric salts; light, heat, electricity &c present, that a protein compound was chemically formed, ready to undergo still more complex changes, at the present day such matter would be instantly devoured, or absorbed, which would not have been the case before living creatures were formed.” Charles Darwin, in a personal letter to Joseph Hooker in 1871, proposed that the origins of life might have occurred in a warm little pond, filled with ammonia and phosphoric salts, light, heat, and electricity. This idea was first introduced by biologist Thomas Huxely, who coined the term abiogenesis. Abiogenesis means the original evolution of life arose from nonlife. Huxley himself was influenced by Louis Pasteur’s experiment in 1859 that disproved spontaneous generation, the belief that current living organisms could arise from nonliving matter. Pasteur's experiment showed that microorganisms do not spontaneously appear in a sterile environment.

This got Huxley thinking about the very first formation of life. Huxley believed that original life had to arise from non-living matter as he wrote in his 1868 essay, “On the Physical Basis of Life.” He argued that life required certain compounds, such as carbon, hydrogen, oxygen, and nitrogen , to undergo several chemical reactions. These reactions likely took place in Earth’s early oceans, where temperature changes and electric sparks mixed the ingredients of life until a complex membrane formed. (Huxley 1868). These ideas are speculations based on the scientific discoveries of the time rather than evidence, however, they have influenced the field of astrobiology.

Darwin’s warm little pond has been interpreted as a metaphor for primordial soup, a mixture of compounds that could have existed on early Earth that lead to the formation of life. The idea has been used as a starting point for understanding the origins of life on our planet and when searching for it on other planets containing similar chemical mixtures. Today, scientists continue searching for environments that could have formed the organic molecules necessary for life, such as amino acids and nucleotides.

Finding the "Warm Little Pond"

One plausible contender for this warm little pond are hydrothermal vents. These vents could have produced prebiotic reactions needed for the formation of amino acids and complex molecules that are the building blocks of life. Some hydrothermal vent fields are an analogue of early Earth, with high alkalinity, metal-rich, heat, high pressure, and minerals that could drive CO2 reduction (Barge 2022, Russell 2006). The super-heated water is typically around 400℃ and shoots out of fissures. The water erodes the fissures as it pours out of the Earth, carrying with it minerals such as iron, sulfur, and hydrogen sulfide.

These environmental conditions could have provided the necessary resources for microbial life to form. Some hydrothermal vents can be in the deep sea or tidal waters where the influxes of water create certain geochemical conditions through wet and dry cycling. Low tide exposes the hydrothermal precipitate to UV radiation and air, which was composed of gases spewed from volcanic activity such as methane, hydrogen sulfide, and significant amounts of carbon dioxide (Bonfio 2017).

Marine hydrothermal vents are not the only ones in question. Terrestrial geysers, such as the hot springs in YellowStone, also provide similar conditions such as high temperature, mineral-rich waters, and high or low pH in freshwater systems. Even in these extreme conditions, thermophiles have been found to live in hot springs and are believed to be some of the earliest forms of life.

Importance

Understanding how life may have evolved in these environments gives us insight into the search for life on other planets. It is thought that moons in our solar system, such as Satrurn’s moons Enceladus and Titan, along with Jupiter’s moon Europa, have subsurface oceans that may provide conditions conducive for hydrothermal activity. On Mars, NASA’s Mars Reconnaissance Orbiter found possible evidence of past hydrothermal vents due to geological formations and mineral deposits in the Eridanian region (Michalski 2017).

The warm little pond concept is a precursor for the origin of life hypotheses of today. The origins of life are still an unsolved scientific mystery, but the search for the environments that could have fostered the formation of organic molecules and the emergence of life continues.

References:

Barge, L. M., & Price, R. E. (2022). Diverse geochemical conditions for prebiotic chemistry in shallow-sea alkaline hydrothermal vents. Nature Geoscience, 15(12), 976–981. https://doi.org/10.1038/s41561-022-01067-1

Bonfio, C. (2017). UV-light-driven prebiotic synthesis of iron–sulfur clusters. Nat. Chem. 9, 1229–1234.

Huxley, T. H. (2015). On the physical basis of life. Forgotten Books.

Michalski, J. R., Dobrea, E. Z., Niles, P. B., & Cuadros, J. (2017). Ancient hydrothermal seafloor deposits in Eridania Basin on Mars. Nature Communications, 8(1). https://doi.org/10.1038/ncomms15978