Nitrogen is an essential element for life and is an integral part of DNA and proteins. Most of the nitrogen on Earth exists in the atmosphere as gaseous nitrogen, denoted as N.2 However, most organisms cannot directly use nitrogen. In modern ecosystems, some microorganisms have specialized enzymes that convert nitrogen into nitrogen.2 It converts gases into a form that other living things can use. Fixed nitrogen These microorganisms Nitrogen fixing bacteria.
But 3 to 4 billion years ago, during a period in Earth's history called the Archean Era, life had not yet evolved and no nitrogen-fixing organisms existed, so scientists studying the origin of life are faced with a classic chicken-and-egg problem: life needed nitrogen to evolve, but before life evolved, there were no microorganisms to convert nitrogen into nitrogen.2 Let's turn gas into something we can use! So where did life get its nitrogen from before there were nitrogen-fixing organisms?
Researchers recently hypothesized that early life on Earth may have obtained fixed nitrogen from lightning. They propose that the high energy of a lightning spark could react with oxygen and N.2 Fixing atmospheric nitrogen2 The gas is converted into other usable forms of nitrogen. Nitrogen oxides.
Geologists have studied the sedimentary rock record to understand nitrogen throughout Earth's history, but they had no way to distinguish lightning-derived nitrogen in rocks from other ancient sources of nitrogen. To explore whether lightning provided fixed nitrogen to early life, researchers led by Dr. Patrick Barth created “lightning” in a jar and tested whether it would react with nitrogen.2 It emitted gases and produced nitrogen oxides that had an identifiable signal.
To simulate lightning, the researchers used electrodes in glass flasks filled with different gas mixtures: To mimic modern-day Earth, Barth and his colleagues used a flask with a composition similar to our current atmosphere, containing 85 percent nitrogen.2 They also used flasks containing an atmosphere similar to that of Archean Earth, which scientists believe was about 83% nitrogen.20% oxygen, 16% carbon dioxide.
The researchers added 50 milliliters (about a quarter cup) of water to the bottom of each flask to allow any nitrogen oxides and other compounds produced during the reaction to dissolve in the water. They discharged each experimental flask to about 50 kilovolts for 15 to 60 minutes — nearly 10 times the voltage of an electric car battery.
The research team developed a device called Quadrupole Gas AnalyzerThey measured the nitrogen compounds in the gases coming out of each flask before and after they were ignited. They found that in the modern experiment, more fixed nitrogen was dissolved in the water than in the gas. But in the Archean experiment, the fixed nitrogen was split almost equally between the water and the gas.
After each reaction, the researchers placed the flask of water into an apparatus that measured the weight of the nitrogen atoms. Gas Source Mass SpectrometerThey explained that nitrogen atoms exist in two main forms with different masses, called isotopes. 14The N isotope is lighter and more abundant in nature, 15The N isotope is heavier and less common. The researchers used mass spectrometer data to calculate the ratios of nitrogen isotopes in the lightning-fixed nitrogen samples. They compared these nitrogen isotope ratios to those in rocks that are 3.1 to 3.8 billion years old to see if there was a match.
The researchers found that the nitrogen isotope ratio of the lightning-produced nitrogen was about 0.1% to 1% lighter than that of the rocks, and suggested that this difference in nitrogen isotopes indicates that most of the nitrogen in the Archean rocks was not produced by lightning.
The researchers also used the lightning flash rate on modern Earth to predict the amount of nitrogen oxides that lightning would produce per year. They estimated that the annual lightning flash rate alone could not have provided enough nitrogen to support ecosystems on early Earth. They explain that there was even less lightning in the Archean than there is today, so even less nitrogen was available to support early life.
The researchers concluded that lightning was not the main source of available nitrogen for early life. Because nitrogen-fixing organisms must have evolved very early in Earth's history, life did not need to rely solely on lightning, they suggested. However, one of the 3.7-billion-year-old rock samples showed nitrogen isotope ratios similar to lightning-fixed nitrogen, leading the researchers to speculate that small amounts of fixed nitrogen from lightning may have supported early life. Furthermore, the researchers suggested that the lightning-fixed nitrogen isotope ratios obtained in this study could be used to investigate how nitrogen is fixed on other planets in the solar system.
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Source: sciworthy.com
