The finding is the first concrete validation of a long-held hypothesis that oxygen was being produced and consumed by that time and that the transition to an oxygenated atmosphere was long term. The results are published in the on-line early edition of the Proceedings of the National Academy of Science, to appear the week of October 16th.
It is generally believed that before 2.4 billion years ago, Earth's atmosphere was essentially devoid of oxygen. Exactly when and how oxygen-producing photosynthesis evolved and began fueling the atmosphere with the gas that much of life depends on has been hotly debated for some time. Plants, algae, and cyanobacteria (blue-green algae) emit oxygen as a waste product of photosynthesis--the process by which sugar, essential for nutrition, is made from light, water, and carbon dioxide.
"Our evidence points to the likelihood that Earth was peppered with small 'oases' of shallow-water, oxygen-producing, photosynthetic microbes around 2.7 billion years ago," stated lead author Jennifer Eigenbrode of Carnegie's Geophysical Laboratory, who collected the data while pursuing her Ph.D. at Penn State. "Over time these oases must have expanded, eventually enriching the atmosphere with oxygen. Our data record this transition."
The researchers discovered changes in fossil isotopes of the life-essential element carbon in a 150 million-year section of rock that included shallow and deepwater sediments from the late Archean period (the Archean lasted from 3.8 to 2.5 billion years ago) in Hamersley Province in Western Australia. Isotopes are different forms of an element's atoms. The relative proportions of carbon and other isotopes in organic matter depend on chemical reactions that happen as the carbon wends its way through an organism's metabolism. There are two stable isotopes of carbon found in nature--12C and 13C--which differ only in the number of neutrons in the nucleus. By far the most abundant variety is in the lighter, 12C. About 1% is 13C, a heavier sibling with an additional neutron; it is the key to understanding photosynthetic organisms.
"Photosynthetic microbes evolved in the shallow water where light was plentiful," explained Eigenbrode. "They used light and CO2 to produce their food, like cyanobacteria do today. They gobbled up 12C and 13C, which became part of the organisms. The results are recorded in the rocks containing the remains for us to find billions of years later. Organisms leave behind different mixes of 12C and 13C depending on what they eat and how they metabolize it. Changes in these chemical fingerprints tell us about changes in how organisms got their energy and food."
In the Archean, microbes that could not live with oxygen--anaerobic organisms--ended up with relatively small amounts of 13C. As oxygen became available in shallow water due to oxygen-producing photosynthesis, anaerobic organisms were out-competed by microbes that had adapted to oxygen. As a result, the amount of 13C increased--first in shallow water, then in deeper water. Changes in the mix of carbon isotopes in these late Archean rocks indicate microbes were learning to live with oxygen well before the atmosphere began accumulating noticeable amounts of oxygen.
Jennifer Eigenbrode | EurekAlert!
Wandering greenhouse gas
16.03.2018 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung
Unique Insights into the Antarctic Ice Shelf System
14.03.2018 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung
Animal photoreceptors capture light with photopigments. Researchers from the University of Göttingen have now discovered that these photopigments fulfill an...
On 15 March, the AWI research aeroplane Polar 5 will depart for Greenland. Concentrating on the furthest northeast region of the island, an international team...
The world’s second-largest ice shelf was the destination for a Polarstern expedition that ended in Punta Arenas, Chile on 14th March 2018. Oceanographers from...
At the 2018 ILA Berlin Air Show from April 25–29, the Fraunhofer Institute for Laser Technology ILT is showcasing extreme high-speed Laser Material Deposition (EHLA): A video documents how for metal components that are highly loaded, EHLA has already proved itself as an alternative to hard chrome plating, which is now allowed only under special conditions.
When the EU restricted the use of hexavalent chromium compounds to special applications requiring authorization, the move prompted a rethink in the surface...
At the ILA Berlin, hall 4, booth 202, Fraunhofer FHR will present two radar sensors for navigation support of drones. The sensors are valuable components in the implementation of autonomous flying drones: they function as obstacle detectors to prevent collisions. Radar sensors also operate reliably in restricted visibility, e.g. in foggy or dusty conditions. Due to their ability to measure distances with high precision, the radar sensors can also be used as altimeters when other sources of information such as barometers or GPS are not available or cannot operate optimally.
Drones play an increasingly important role in the area of logistics and services. Well-known logistic companies place great hope in these compact, aerial...
16.03.2018 | Event News
13.03.2018 | Event News
08.03.2018 | Event News
16.03.2018 | Earth Sciences
16.03.2018 | Physics and Astronomy
16.03.2018 | Life Sciences