{"id":3191,"date":"2021-11-09T10:00:00","date_gmt":"2021-11-09T10:00:00","guid":{"rendered":"https:\/\/modernsciences.org\/staging\/4414\/?p=3191"},"modified":"2021-10-26T07:14:24","modified_gmt":"2021-10-26T07:14:24","slug":"earths-oxygen-took-a-while-to-settle-in-and-we-may-have-asteroids-to-blame-for-it","status":"publish","type":"post","link":"https:\/\/modernsciences.org\/staging\/4414\/earths-oxygen-took-a-while-to-settle-in-and-we-may-have-asteroids-to-blame-for-it\/","title":{"rendered":"Earth\u2019s Oxygen Took a While to Settle In\u2014And We May Have Asteroids to Blame For It"},"content":{"rendered":"\n

We might take the oxygen in our planet\u2019s atmosphere for granted now, but it certainly wasn\u2019t always there. In fact, research from earlier this year suggests that we may have volcanic eruptions to thank for helping the first cyanobacteria put out their waste product<\/a> that we now need to live. And, by the looks of things, it may not even stick around forever, as it appears our planet\u2019s oxygen is doomed not to stay on this planet<\/a> (though not for a very long while, anyway, so no need to panic).<\/p>\n\n\n\n

Nevertheless, it\u2019s interesting to see how much more we\u2019re learning about our planet\u2019s past and future with each passing day in science\u2014and this day seems set to follow that trend. New research made available in the journal Nature Geoscience<\/em> revealed that our planet may have been pelted with much more space rocks than originally thought. And, given that these impacts were determined to have had a profound effect on our planet\u2019s atmospheric chemistry, these impacts may have delayed the eventual oxygenation of our atmosphere far more than we thought.<\/p>\n\n\n\n

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Meteor Crater is an impact site located in the northern Arizona desert of the United States of America. It was found to have been made roughly 50,000 years ago after a 50-m (160-ft) asteroid hit the area during the Pleistocene epoch. Earth would have been pelted by impacts just like this, with impactor sizes across the board from small to large, very early on in its planetary life. (NASA Earth Observatory\/Wikimedia Commons, 2009) <\/figcaption><\/figure><\/div>\n\n\n\n

The research effort, led by Southwest Research Institute planetary geologist Simone Marchi, focused on analyzing impact spherules<\/em>\u2014rock particles embedded in today\u2019s crust formed from once-molten crust resulting from high-energy impacts from impactors like asteroids. The molten crust, ejected from the surface after an impact, blanketed the surface soon after as tiny particles of hardened crustal rock.<\/p>\n\n\n\n

In the words of co-author Nadja Drabon, researcher for both the Stanford University Department of Geological Sciences and the Harvard University Department of Earth and Planetary Sciences: \u201cIn recent years, a number of new spherule layers have been identified in drill cores and outcrops, increasing the total number of known impact events during the early Earth.\u201d<\/p>\n\n\n\n

“Current bombardment models underestimate the number of late Archean spherule layers,” said Marchi. “[This suggests] the impactor flux (the rate of impactor collisions) at that time was up to ten (10) times higher than previously thought.”<\/p>\n\n\n\n

Marchi and team were led to this result by the amount of these spherules that people have observed from drilling and excavations, implying that scientists may have underestimated the number of asteroid collisions the Earth may have experienced during the Archaean eon<\/em>\u2014the second eon in Earth\u2019s geologic history, and the time when the crust eventually cooled enough for continents to form and the earliest life on Earth started to appear.<\/p>\n\n\n\n

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The Cretaceous-Paleogene extinction event, often shortened to the K-T boundary event, is famous for having ended the Age of Reptiles, which also spelled doom for the non-avian dinosaurs alive at the time. An artistic impression of what the event may have looked like was done by artist Donald Davis. An earlier Earth\u2014even earlier than the time shown here\u2014would have been pelted by impactors of this size much more frequently. (Davis\/Wikimedia Commons, 1994) <\/figcaption><\/figure><\/div>\n\n\n\n

As asteroid impacts carry a lot of kinetic energy with them moments before impact, that energy is transferred to the planet in the immediate vicinity of the impact site, melting surrounding rock and superheating the air around the impactor.<\/p>\n\n\n\n

According to co-author and Stanford University astronomer and geologist Laura Schaefer, impacts by objects over 6 mi (9.7 km) in diameter would have \u201cproduced enough reactive gases to completely consume low levels of atmospheric oxygen\u201d\u2014meaning the still-small amounts of oxygen that would have been present at the time will have likely reacted and would have been consumed instead of just staying around.<\/p>\n\n\n\n

“This pattern was consistent with evidence for so-called ‘whiffs’ <\/em>of oxygen, relatively steep but transient increases in atmospheric oxygen that occurred around 2.5 billion years ago. We think that the whiffs were broken up by impacts that removed the oxygen from the atmosphere.\u201d<\/p>\n\n\n\n

Follow-up modeling revealed that these bombardments would have functioned as an oxygen sink<\/em>, or a cause for a dip in oxygen levels, similar to how rock weathering exposes metals embedded within to atmospheric oxidation. It was only when oxygen production exceeded these oxygen sink effects did the Earth finally start to build up the atmosphere we now cannot live without\u2014an event called the Great Oxidation Event <\/em>(GOE).<\/p>\n\n\n\n

Marchi continued: “Impact vapors caused episodic low oxygen levels for large spans of time preceding the GOE. As time went on, collisions became progressively less frequent and too small to be able to significantly alter post-GOE oxygen levels. The Earth was on its course to become the current planet.”<\/p>\n\n\n\n

References<\/h2>\n\n\n\n