New Hypothesis on the Origin of Life Proposed By Research Scientists Armen Mulkidjanian of the University of Osnabrueck, Germany and Michael Galperin of the U.S. National Institutes of Health

 

The new hypothesis suggests that life on Earth originated at photosynthetically-active porous structures made of zinc sulfide similar to deep-sea hydrothermal vents. Credit: The Institute for Exploration, the University of Rhode Island (URI) Graduate School of Oceanography (GSO), and the URI Institute for Archaeological Oceanography.

A recently developed hypothesis suggested by two research scientists; Armen Mulkidjanian of the University of Osnabrueck, Germany and Michael Galperin of the U.S. National Institutes of Health postulates that the origin of life on Earth may have developed "at photosynthetically-active porous structures made of zinc sulfide similar to deep-sea hydrothermal vents."

The widely accepted, definitive example of the classically regarded experiment on the origin of life conducted by chemists Stanley Miller and Harold Urey in 1953 established that the inorganic substances, "a mixture of methane, hydrogen, ammonia and water vapor" along with electrical discharges to simulate lightning that were present in the primordial Earth atmosphere, they believed, was capable of producing amino acids, the building blocks of life.

The significance of the Mulkidjanian/Galperin hypothesis that has been published and is available for discussion at the Biology Direct site on the internet is that it expands upon and broadens our understanding of the processes that combined to bring about life on Earth.

The current-day researchers' theory posits that life originated on Earth in the vicinity of "photosynthetically-active porous structures, similar to deep-sea hydrothermal vents, made of zinc sulfide (more commonly known as phosphor). They argue that under the high pressure of a carbon-dioxide-dominated atmosphere, zinc sulfide structures could form on the surface of the first continents, where they had access to sunlight. Unlike many existing theories that suggest UV radiation was a hindrance to the development of life, Mulkidjanian and Galperin think it actually helped.

“The problem of the origin of life is such that you have to answer a set of different questions to explain how life has originated,” says lead author Mulkidjanian. “We just provide answers to the problem of energetics of the origin of life.”

The Miller and Urey experiment "assumed that the early Earth had a reducing atmosphere, which meant it had large amounts of hydrogen and almost no oxygen."As the Miller/Urey experiment was studied over time "According to Mulkidjanian, the debate about whether life could arise from chemical reactions began to change when scientists started to question the atmospheric conditions used by Miller and Urey."

 

 Miller-Urey experiment (1953). Image: YassineMrabet, via Wikipedia.

The belief that the primordial Earth had a reducing atmosphere has now been replaced by the idea that: "Earth had a neutral atmosphere, composed primarily of carbon dioxide, with smaller amounts of nitrogen and hydrogen, similar to the modern atmospheres of Mars and Venus. Researchers who have repeated the Miller-Urey experiment under the new atmospheric assumptions, including Miller, have shown that this new mixture does not produce amino acids."

Mulkidjanian explains: “After it became clear that the origin of the atmosphere was made of carbon dioxide,... there was no physically or chemically plausible hypothesis of the origin of life.” In other words, organic life is dependent on some form of energy that emanates chemical reactions or solar energy.

“If you have an atmosphere of carbon dioxide, you need, in addition, a source of electrons to reduce carbon dioxide if you want to make complex compounds,” Mulkidjanian explains.

The Mulkidjanian “Zn world hypothesis presents a different version of the prebiotic Earth atmosphere—one in which zinc sulfide plays a major role in the development of life. In nature, zinc sulfide particles precipitate only at deep-sea hydrothermal vents." It is important to remember that zinc sulfide particles have a unique ability to store light energy and it is this "ability to store light makes zinc sulfide an important factor in the discussion on life’s origin." Mulkidjanian explains: once illuminated by UV light, zinc sulfide can efficiently reduce carbon dioxide, just as plants do." And lending credence to their "hypothesis, Mulkidjanian and Galperin analyzed the metal content of modern cells and found “surprisingly high levels of zinc,” particularly in the complexes of proteins with DNA and RNA molecules."

“We have found that proteins that are considered ‘evolutionarily old’ and particularly those related to handling of RNA specifically contain large amounts of zinc,” Mulkidjanian says.

So there is a high likelihood that the original forms of life on Earth "evolved in a zinc-rich environment."
“We cannot explain fully the properties of modern organisms unless we understand how life has originated,” says Mulkidjanian.

The Mulkidjanian/Galperin hypothesis holds significant importance to theorists and researchers in astrobiology engaged in the study of the origins of life.

“If this hypothesis is adopted in the origins of life community, it would represent a real conceptual shift, and so it would be significant,” says NASA astrobiologist Max Bernstein. “Whether it will be adopted or not eventually I cannot say, but I expect that many will want to see experimental evidence of the viability of reactions consistent with the hypothesized scheme under prebiotic conditions.”

Source: Astrobio.net, by Anuradha K. Herath