Scientists studying micrometeorites, space dust, revealed the composition of Earth's atmosphere 2.7 billion years ago and discovered that its upper layer contained a lot of oxygen, long before the first single-celled organisms used photosynthesis
Australian scientists studying the oldest micrometeorites (space dust) found have made a surprising discovery about the chemistry of Earth's atmosphere 2.7 billion years ago.
The findings of the new study were published in the journal Nature in an article led by Dr. Andrew Tomkins and a team from the School of Earth, Atmospheric and Environmental Sciences at Monash University together with scientists from the Australian Synchrotron and Imperial College London. The researchers challenge the accepted hypothesis that the atmosphere was low in oxygen at that time. The findings show instead that Earth's upper atmosphere contained the same amount of oxygen as it does today, and that a layer of methane haze separated the oxygen-rich layer from the oxygen-poor lower atmosphere.
Dr. Tomkins explains how the team extracted micrometeorites from ancient limestone samples collected in the Pilbara region of Western Australia and studied at the Monash Center for Electron Microscopy at Monash University and the Australian Synchrotron.
"Thanks to the use of the most advanced microscope, we discovered that most of the micrometeorites were once part of a group of iron meteorites and that the iron inside them turned into iron oxides in the upper atmosphere, which indicated a greater than expected concentration of oxygen," said Dr. Tomkins.
"These were exciting findings because this is the first time anyone has found a way to sample the chemistry of the upper atmosphere," he said.
Dr. Matthew Ganj - an expert in modern cosmic dust performed calculations that showed that the concentration of oxygen in the upper atmosphere had to be close to its levels today to explain the observations.
"This was a surprise, because the long-established estimate is that the Earth's lower atmosphere was very poor in oxygen 2.7 billion years ago; The question of where so much oxygen got to the upper atmosphere before the appearance of photosynthetic organisms was a real puzzle," said Dr. Genge.
Dr. Tomkins explained that the research results suggest that at that time the atmosphere was arranged in a stratified manner with low vertical mixing, and higher levels of oxygen in the upper atmosphere were produced from the decomposition of carbon dioxide by ultraviolet light.
"A possible explanation for the layering of the atmosphere was a layer of methane haze at a medium height. The methane absorbed ultraviolet light, released heat and created a hot zone in the atmosphere that prevented vertical mixing." said Dr. Tomkins.
"It's amazing to think that by studying fossil particles of space dust the width of a human hair, we can gain new insights into the chemical composition of the Earth's upper atmosphere, billions of years ago." added Dr. Tomkins.
"The next step of our research will be to extract micrometeorites from a series of rocks covering over a billion years of Earth's history in order to learn more about the changes in atmospheric chemistry and composition over geological time periods. We will mainly focus on the great oxidation event which occurred 2.4 billion years ago when there was a sudden jump in the concentration of oxygen in the lower atmosphere."
One response
It is possible that the oxygen was part of the components of the cloud of matter from which the Earth was formed.
The accepted explanation is that the material cloud was created in a supernova explosion of a star of the generation that preceded the sun.
The oxygen is part of the nuclear combustion products of the exploded star, in the intermediate layers that surround the core. The oxygen-carbon layer is a remnant of an earlier fusion stage, before the last combustion stage (cobalt to iron) before the supernova explosion.
Since the (atomic) combustion efficiency is not perfect, some of the elements formed in the combustion are ejected to outer layers and do not continue the combustion in the core of the star, which creates the heavier elements.