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Nov 30, 2023

Where Did Life First Form on Earth? Complex NASA Hydrothermal Reactor Provides New Evidence

By Jet Propulsion LaboratoryMay 3, 2020 A seafloor vent called a “white smoker”

By Jet Propulsion LaboratoryMay 3, 2020

A seafloor vent called a "white smoker" spews mineral-rich water into the ocean and serves as an energy hub for living creatures. Some scientists think life on Earth may have begun around similar vents on the ocean floor billions of years ago. Credit: NOAA/C. German (WHOI)

By mimicking rocky seafloor chimneys in the lab, scientists have produced new evidence that these features could have provided the right ingredients to kick-start life.

Where did life first form on Earth? Some scientists think it could have been around hydrothermal vents that may have existed at the bottom of the ocean 4.5 billion years ago. In a new paper in the journal Astrobiology, scientists at NASAEstablished in 1958, the National Aeronautics and Space Administration (NASA) is an independent agency of the United States Federal Government that succeeded the National Advisory Committee for Aeronautics (NACA). It is responsible for the civilian space program, as well as aeronautics and aerospace research. Its vision is "To discover and expand knowledge for the benefit of humanity." Its core values are "safety, integrity, teamwork, excellence, and inclusion." NASA conducts research, develops technology and launches missions to explore and study Earth, the solar system, and the universe beyond. It also works to advance the state of knowledge in a wide range of scientific fields, including Earth and space science, planetary science, astrophysics, and heliophysics, and it collaborates with private companies and international partners to achieve its goals." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]">NASA's Jet Propulsion Laboratory describe how they mimicked possible ancient undersea environments with a complex experimental setup. They showed that under extreme pressure, fluid from these ancient seafloor cracks mixed with ocean water could have reacted with minerals from the hydrothermal vents to produce organic molecules — the building blocks that compose nearly all life on Earth.

In particular, the research lays important groundwork for in-depth studies of such ocean worlds as SaturnSaturn is the sixth planet from the sun and has the second-largest mass in the Solar System. It has a much lower density than Earth but has a much greater volume. Saturn's name comes from the Roman god of wealth and agriculture." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]">Saturn's moon Enceladus and JupiterJupiter is the largest planet in the solar system and the fifth planet from the sun. It is a gas giant with a mass greater then all of the other planets combined. Its name comes from the Roman god Jupiter." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]">Jupiter's moon Europa, which are both thought to have liquid-water oceans buried beneath thick icy crusts and may host hydrothermal activity similar to what's being simulated at JPLThe Jet Propulsion Laboratory (JPL) is a federally funded research and development center that was established in 1936. It is owned by NASA and managed by the California Institute of Technology (Caltech). The laboratory's primary function is the construction and operation of planetary robotic spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA's Deep Space Network. JPL implements programs in planetary exploration, Earth science, space-based astronomy and technology development, while applying its capabilities to technical and scientific problems of national significance." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]">JPL. This area of research belongs to a field of study known as astrobiology, and the work was done by the JPL Icy Worlds team as part of the former NASA Astrobiology Institute.

Some scientists think the story of life on Earth may have started around hydrothermal vents at the bottom of the ocean 4.5 billion years ago. Scientists at NASA's Jet Propulsion Laboratory mimicked those ancient undersea environments with a complex experimental setup.

To simulate conditions that might have existed on the ocean floor of a newly formed Earth, before the sea teemed with life, then-graduate student Lauren White and colleagues conducted an experiment that brought together three key ingredients: hydrogen-rich water, like the kind that could have flowed out from beneath the seafloor through vents; seawater enriched with carbon dioxide, as it would have been from the ancient atmosphere; and a few minerals that might have formed in that environment.

White and colleagues — including her graduate advisor, retired JPL scientist Michael Russell — simulated vents that didn't spew particularly hot water (it was only about 212 FahrenheitThe Fahrenheit scale is a temperature scale, named after the German physicist Daniel Gabriel Fahrenheit and based on one he proposed in 1724. In the Fahrenheit temperature scale, the freezing point of water freezes is 32 °F and water boils at 212 °F, a 180 °F separation, as defined at sea level and standard atmospheric pressure. " data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]">Fahrenheit, or 100 degrees CelsiusThe Celsius scale, also known as the centigrade scale, is a temperature scale named after the Swedish astronomer Anders Celsius. In the Celsius scale, 0 °C is the freezing point of water and 100 °C is the boiling point of water at 1 atm pressure." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]">Celsius). One major challenge with creating the experimental setup was maintaining the same pressure found 0.6 miles (1 kilometer) below the ocean surface — about 100 times the air pressure at sea level. Previous experiments have tested similar chemical reactions in individual high-pressure chambers, but White and her colleagues wanted to more fully replicate the physical properties of these environments, including the way the fluids flow and mix together. This would require maintaining the high pressure in multiple chambers, which added to the complexity of the project. (Because a crack or leak in even a single high-pressure chamber poses the threat of an explosion, it's a standard operating procedure in such cases to install a blast shield between the apparatus and the scientists.)

Lauren White, a scientist at NASA's Jet Propulsion Laboratory, adjusts an experiment that simulates how ancient seawater and fluid from hydrothermal vents could have reacted with minerals from the seafloor to create organic molecules 4.5 billion years ago. The image was taken at JPL in 2014. Credit: NASA/JPL-Caltech

The scientists wanted to determine whether such ancient conditions could have produced organic molecules — those containing carbon atoms in loops or chains, as well as with other atoms, most commonlyhydrogen. Examples of complex organic molecules include amino acids<div class="cell text-container large-6 small-order-0 large-order-1"><div class="text-wrapper"><br />Amino acids are a set of organic compounds used to build proteins. There are about 500 naturally occurring known amino acids, though only 20 appear in the genetic code. Proteins consist of one or more chains of amino acids called polypeptides. The sequence of the amino acid chain causes the polypeptide to fold into a shape that is biologically active. The amino acid sequences of proteins are encoded in the genes. Nine proteinogenic amino acids are called "essential" for humans because they cannot be produced from other compounds by the human body and so must be taken in as food.<br /></div></div>" data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]">amino acids, which can eventually form DNADNA, or deoxyribonucleic acid, is a molecule composed of two long strands of nucleotides that coil around each other to form a double helix. It is the hereditary material in humans and almost all other organisms that carries genetic instructions for development, functioning, growth, and reproduction. Nearly every cell in a person's body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA)." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]">DNA and RNARibonucleic acid (RNA) is a polymeric molecule similar to DNA that is essential in various biological roles in coding, decoding, regulation and expression of genes. Both are nucleic acids, but unlike DNA, RNA is single-stranded. An RNA strand has a backbone made of alternating sugar (ribose) and phosphate groups. Attached to each sugar is one of four bases—adenine (A), uracil (U), cytosine (C), or guanine (G). Different types of RNA exist in the cell: messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA)." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]">RNA.

But just as eggs, flour, butter, and sugar aren't the same thing as a cake, the presence of both carbon and hydrogen in the early oceans doesn't guarantee the formation of organic molecules. While a carbon and a hydrogen atomAn atom is the smallest component of an element. It is made up of protons and neutrons within the nucleus, and electrons circling the nucleus." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]">atom might reasonably bump into each other in this prehistoric ocean, they wouldn't automatically join to form an organic compound. That process requires energy, and just like a ball won't roll up a hill by itself, carbon and hydrogen won't bind together without an energetic push.

A previous study by White and her colleagues showed that water pulsing through hydrothermal vents could have formed iron sulfides. By acting as a catalyst, iron sulfides could provide that energetic push, lowering the amount of energy required for carbon and hydrogen to react together, and increasing the likelihood they would form organics.

The new experiment tested whether this reaction would have been likely to occur under the physical conditions around ancient seafloor vents, if such vents existed at the time. The answer? Yes. The team created formate and trace amounts of methane, both organic molecules.

Naturally occurring methane on Earth is produced largely by living organisms or through the decay of biological material, including plants and animals. Could methane on other planets also be a sign of biological activity? To use methane to search for life on other worlds, scientists need to understand both its biological and non-biological sources, such as the one identified by White and her colleagues.

"I think it's really significant that we showed that these reactions take place in the presence of those physical factors, like the pressure and the flow," said White. "We are still a long way from demonstrating that life could have formed in these environments. But if anyone ever wants to make that case, I think we’ll need to have demonstrated the feasibility of every step of the process; we can't take anything for granted."

The work builds on Michael Russell's hypothesis that life on Earth may have formed at the bottom of Earth's early ocean. The formation of organic molecules would be a major step in this process. Scientists in the same JPL research group have explored other aspects of this work, such as replicating the chemical conditions in the early ocean to demonstrate how amino acids might form there. However, the new study is unique in the way it recreated the physical conditions of those environments.

In the next few years, NASA will launch Europa Clipper, which will orbit Jupiter and perform multiple flybys of the icy moon Europa. Scientists believe plumes there may spew water into space from the moon's ocean, which lies beneath about 2 to 20 miles (3 to 30 kilometers) of ice. These plumes could provide information about possible hydrothermal processes at the bottom of the ocean, thought to be about 50 miles (80 kilometers) deep. The new paper contributes to a growing understanding of the chemistry that might take place in oceans other than our own, which will help scientists interpret the findings of that mission and others to come.

Reference: "Simulating Serpentinization as It Could Apply to the Emergence of Life Using the JPL Hydrothermal Reactor" by Lauren M. White, Takazo Shibuya, Steven D. Vance, Lance E. Christensen, Rohit Bhartia, Richard Kidd, Adam Hoffmann, Galen D. Stucky, Isik Kanik and Michael J. Russell, 2 March 2020, Astrobiology.DOI: 10.1089/ast.2018.1949