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First Life Forms On Earth May Have Emerged From Primitive Ponds, Not Oceans

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Earth's first life forms were more likely to have originated from primitive ponds and not from oceans, according to a new MIT study.

Researchers at the Massachusetts Institute of Technology said that shallow bodies of waters such as ponds that are only 10 centimeters deep, had higher concentrations of nitrogen, an element considered as a key ingredient for life on Earth.

The study opined that nitrogenous oxides in shallow ponds had a good chance of reacting with other molecules and give life to early living organisms. Establishing this kind of life-catalyzing presence would have been more difficult to achieve in deeper oceans.

"It's much easier to have that happen in a pond," said Sukrit Ranjan, the study's lead author, and a postdoc at MIT's Department of Earth, Atmospheric and Planetary Sciences.

Nitrogen-Based Hypotheses

There are many theories on how life originated on Earth some 3.9 billion years ago. Ranjan's previous work indicated that volcanoes may have played a role in the origin of life on Earth, particularly sulfidic anions that could have sped up chemical reactions to transform prebiotic molecules into ribonucleic acid or RNA.

In the origin of life hypotheses involving deep oceans, nitrogenous oxides possibly reacted with carbon dioxides to form the first molecular building blocks.

Other hypotheses involve nitrogen and ribonucleic acid or RNA molecules. Scientists believe that free-floating RNA molecules could have been chemically induced after being in contact with nitrogenous oxides. This process might have formed the first molecular chains of life in either oceans or shallow ponds.

Remnants of nitrogen breakdown in the Earth's atmosphere produced an abundance of nitrogenous oxides in bodies of water. Scientists said such occurrence likely happened when lightning produced enough energy and broke down the molecules of atmospheric nitrogen.

Early Life Formed In Ponds, Not Oceans

The MIT study identified two significant effects or "sinks" that could have destroyed large portions of nitrogenous oxides in oceans. It stated that ultraviolet light and dissolved iron possibly suppressed the nitrogen concentrations in the ocean by as much as a factor of 1,000, relative to what was assumed before. Broken down nitrogenous oxide compounds meshed back into the atmosphere as gaseous nitrogen.

In shallow ponds, however, the "sinks" would have less of an effect on the concentration of nitrogenous oxides, allowing compounds and molecules to interact and catalyze the first living organisms.

Ranjan said the molecules would have been an inevitable part of the environment but whether they were integral to the origin of life is still something that scientists are trying to discover.

"There's no real 'aha' moment. It's more like building up patiently one observation after another, and the picture that's emerging is that overall, many prebiotic synthesis pathways seem to be chemically easier in ponds than oceans," Ranjan added.

The study is published in Geochemistry, Geophysics, Geosystems journal.

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