SuppliedA team of geochemists at the University of Alberta in the department of Earth and atmospheric sciences, including professor Long Li, are working to uncover the chemical processes that contributed to life on early Earth.
“We know right now that ammonium sulfate is a very important fertilizer for biological processes. This also applies to the early Earth,” Li explained.
He added that “ammonia is a very important chemical for not only the evolution of life, but also the synthesis of the first life.” This is because chemical compounds, including reduced carbon and nitrogen, are needed to synthesize the building blocks for life, such as amino acids, Li said.
Therefore, “ammonia or ammonium is a key of those chemical compounds for the origin of life, as well as the development of habitable environments on the early Earth,” according to Li.
We know that ammonium is crucial for life, but Li shared that it was not present on early Earth. The puzzling question scientists have been asking for years is: “If we need ammonium on early Earth [for the origin of life], where did it come from?”
Abiotic nitrogen reduction: A key reaction for life on early Earth
The team found evidence for a process called abiotic nitrogen reduction (ANR), which is a very simple chemical reaction where nitrogen and hydrogen react to make ammonia, Li explained.
“In modern industry, ANR is very commonly used to synthesize fertilizers,” Li said. The reaction is very easy to make in industry because of the “catalysts and high-pressure devices” in place to make the reaction occur.
Li explained that it is more challenging for this reaction to occur in natural environments, because it is “difficult to break the very strong triple bond in nitrogen to make ammonia.”
This is why, “although this reaction has been hypothesized as a very important reaction on the early Earth, it hasn’t been demonstrated or observed to occur in natural environments,” Li said.
The paradox that links astrophysics and geochemistry
The team’s work also relates to a concept from astrophysics called the faint young sun paradox. Li explained that astrophysicists found that the sun, like the Earth, evolved over a long time.
Li described that “at the time Earth was born about 4.5 billion years ago, the sun at that time was also at its young age and its luminosity, or the energy of the sunlight reaching Earth, was also weaker.”
The luminosity of the sun at that time was about 70 per cent of what reaches Earth now, he shared. Due to the low energy the Earth was receiving, “the Earth’s surface temperature was much lower than [it is] today, well below the freezing point of water.”
This information suggests that “the entire Earth should have been frozen from approximately 4.5 billion years ago to two billion years ago.”
However, Li countered this idea by explaining that “from the study of rock records, paleoclimatologists have found that Earth has been fairly warm from at least 4.4 billion years ago.”
He concluded his explanation by stating that this contradiction is what is known as the faint young sun paradox.
This paradox is still an open question, Li said. There have been many hypotheses proposed to solve it.
The role of greenhouse gases and ammonia
He shared that one of these hypotheses is “the presence of greenhouse gases on the early Earth’s atmosphere.” According to him, “some other gases can even enlarge greenhouse gas effects,” including ammonia.
“Overall ammonium has been one of the key components that helps to answer questions related to habitability and origin of life on early Earth,” Li said.
The next steps for Li and his team are to continue researching what their findings suggest about how widespread the conditions for life may have been on early Earth.
“[They] will be looking at this not only on a temporal scale, but also on a spatial scale to look at more samples worldwide to see how common this process is,” Li explained.
He said they are also interested in determining the ammonia production rate and using this data “to do quantitative modelling and a better assessment of this reaction and its contribution to the development of habitable environments and the origin of life on early Earth.”
