The mystery of how Earth’s atmosphere formed has long been debated by scientists. However, some scientists believe that some of Earth’s atmosphere may have been brought to the planet by comets billions of years ago. A new study has found evidence to back up this theory.
In a new study published in Nature Communications, scientists have been analyzing tiny samples of ancient air trapped within water bubbles found in quartz dating back over 3 billion years.
The researchers found the air in the rocks was partly made up of an extremely rare form of the chemical element xenon. What makes this chemical element known as U-Xe so rare is that it isn’t usually found on Earth. It has not been found in any meteorites, and the component is not present in Earth’s mantle.
Consequently, the scientists have concluded that the U-Xe must have been added to Earth after a primordial atmosphere had developed. Therefore, comets would be the best candidates for carrying the U-Xe to the planet.
Prof. Ray Burgess, from Manchester’s School of Earth and Environmental Sciences and a co-author, explained in a statement:
“The Earth formed too close to the Sun for volatile elements, such as U-Xe, to easily condense, and they would have rapidly boiled off the surface and been lost to space.
“The reason that oceans and an atmosphere exist at all is because volatiles were still being added after the Earth formed. The puzzle is in identifying where the volatiles came from and what objects carried them to the early Earth.
“The difficulty is that many of the different volatile ingredients that were originally added have been thoroughly mixed together by geological processes during Earth’s long geological history.”
The researchers used drill cores from the Barberton area of South Africa; rocks from this region are extremely old and very well preserved. In the Barberton quartz, it was discovered that the 3.3 billion-year-old U-Xe had a composition that was very different from the xenon found in the Earth’s atmosphere today.
Lead author Dr. Guillaume Avice from CRPG explained:
“We measured the amount and isotopic abundance of xenon in the 3.3 billion-year-old air with unparalleled precision.
“Xenon is a noble gas which, being chemically inert and having nine isotopes, is an ideal element to reveal the xenon isotopic composition in the Earth’s primary atmosphere. This also makes it an ideal way of finding out where the atmosphere came from.”
Prof. Bernard Marty, who initiated the study and who is also based at CRPG, said:
“Our study reveals that 3 billion years ago there was already a xenon component in the Earth’s atmosphere different from solar gases and in asteroids. One possibility is that this xenon was from comets.”
Dr. Avice explained how the discovery shows the research possibilities for studying gases found trapped deep in the earth:
“The study of gases trapped in ancient rocks opens new perspectives in our understanding of the origin and evolution of Earth’s volatile elements, which are key factors for our planet’s habitability.”
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