{"598840":{"#nid":"598840","#data":{"type":"news","title":"A Popular Tool to Trace Earth\u2019s Oxygen History Can Give False Positives","body":[{"value":"\u003Cp\u003EFor researchers pursuing the primordial history of oxygen in Earth\u0026rsquo;s atmosphere, a new study might sour some \u0026ldquo;Eureka!\u0026rdquo; moments. A contemporary tool used to trace oxygen by examining ancient rock strata\u0026nbsp;\u003Ca href=\u0022https:\/\/doi.org\/10.1038\/s41467-017-01694-y\u0022 rel=\u0022noopener noreferrer\u0022 target=\u0022_blank\u0022\u003Ecan produce false positives, according to the study\u003C\/a\u003E, and the wayward results can mask as exhilarating discoveries.\u003C\/p\u003E\r\n\r\n\u003Cp\u003ECommon molecules called\u0026nbsp;\u003Ca href=\u0022https:\/\/www.youtube.com\/watch?v=011Bj5USal8\u0022 rel=\u0022noopener noreferrer\u0022 target=\u0022_blank\u0022\u003Eligands\u003C\/a\u003E\u0026nbsp;can bias the results of a popular chemical tracer called the chromium (Cr) isotope system, which is used to test sedimentary rock layers for clues about atmospheric oxygen levels during the epoch when the rock formed. Researchers at the Georgia Institute of Technology have demonstrated in the lab that many ligands could have created a signal very similar to that of molecular oxygen.\u003C\/p\u003E\r\n\r\n\u003Cp\u003E\u0026ldquo;There are some geographical locations and ancient situations where measurable signals could have been generated that had nothing to do with how much oxygen was around,\u0026rdquo; said\u0026nbsp;\u003Ca href=\u0022http:\/\/reinhard.gatech.edu\/people.html\u0022 rel=\u0022noopener noreferrer\u0022 target=\u0022_blank\u0022\u003EChris Reinhard\u003C\/a\u003E, one of the study\u0026rsquo;s lead authors. Though the new research may impact how some recent findings are assessed, that doesn\u0026rsquo;t mean the tool isn\u0026rsquo;t useful overall.\u003C\/p\u003E\r\n\r\n\u003Ch4\u003E\u003Cstrong\u003ERock record tool\u003C\/strong\u003E\u003C\/h4\u003E\r\n\r\n\u003Cp\u003E\u0026ldquo;We\u0026rsquo;re not trying to revolutionize the way the tool is viewed,\u0026rdquo; said\u0026nbsp;\u003Ca href=\u0022http:\/\/tang.eas.gatech.edu\/group\/\u0022 rel=\u0022noopener noreferrer\u0022 target=\u0022_blank\u0022\u003EYuanzhi Tang\u003C\/a\u003E, who co-led the study. \u0026ldquo;This is about understanding its possible limitations to make discerning use of it in particular cases.\u0026rdquo;\u003C\/p\u003E\r\n\r\n\u003Cp\u003ETang and Reinhard, both assistant professors of biogeochemistry in Georgia Tech\u0026rsquo;s School of Earth and Atmospheric Sciences,\u0026nbsp;\u003Ca href=\u0022https:\/\/doi.org\/10.1038\/s41467-017-01694-y\u0022 rel=\u0022noopener noreferrer\u0022 target=\u0022_blank\u0022\u003Epublished their team\u0026rsquo;s results in a study on November 17, 2017, in the journal\u0026nbsp;\u003Cem\u003ENature Communications\u003C\/em\u003E\u003C\/a\u003E. Their work was funded by the NASA Astrobiology Institute, the NASA Exobiology program, and the Agouron Institute.\u003C\/p\u003E\r\n\r\n\u003Cp\u003E\u0026ldquo;On a global level, the chromium isotope system is still a great indicator of atmospheric oxygen levels through the ages,\u0026rdquo; Tang said. \u0026ldquo;The issue we exposed in the lab is more local with isolated samples, especially during eras when there wasn\u0026rsquo;t much atmospheric oxygen.\u0026rdquo;\u003C\/p\u003E\r\n\r\n\u003Ch4\u003E\u003Cstrong\u003ELeaping ligands\u003C\/strong\u003E\u003C\/h4\u003E\r\n\r\n\u003Cp\u003EWithout a dominant oxygen presence,\u0026nbsp;\u003Ca href=\u0022https:\/\/www.iupac.org\/publications\/ci\/2012\/3404\/pp4_wg139.html\u0022 rel=\u0022noopener noreferrer\u0022 target=\u0022_blank\u0022\u003Eligands\u003C\/a\u003E\u0026nbsp;likely made a great reactive substitute, as the researchers demonstrated in reactions with chromium. Like oxygen, ligands strongly attract electron pairs, which is what characterizes them as a chemical group.\u003C\/p\u003E\r\n\r\n\u003Cp\u003EAnd like reactions with oxygen, reactions with ligands enable metals like chromium to move around more easily in the world. In this case, the researchers were interested in organic ligands, ligands that contain carbon.\u0026nbsp;\u003C\/p\u003E\r\n\r\n\u003Cp\u003EThey were more apt to match oxygen\u0026rsquo;s mobility effect on chromium that made it end up as the signals in sedimentary rock that scientists, today, look for as a sign of\u0026nbsp;\u003Ca href=\u0022https:\/\/www.scientificamerican.com\/article\/origin-of-oxygen-in-atmosphere\/\u0022 rel=\u0022noopener noreferrer\u0022 target=\u0022_blank\u0022\u003Eancient atmospheric oxygen\u003C\/a\u003E.\u003C\/p\u003E\r\n\r\n\u003Cp\u003EHere\u0026rsquo;s roughly how the chromium isotope system works, followed by how organic ligands could make for false positives.\u003C\/p\u003E\r\n\r\n\u003Ch4\u003E\u003Cstrong\u003EChromium rollercoaster\u003C\/strong\u003E\u003C\/h4\u003E\r\n\r\n\u003Cp\u003EThe Earth is an enormous chemical laboratory performing reactions in conditions varying from arctic cold to volcanic heat, and from crushing ocean depths to no-pressure upper atmospheres. Winds and waves sweep around materials like turbulent conveyor belts, depositing some in sediments that later turn to stone.\u003C\/p\u003E\r\n\r\n\u003Cp\u003EChromium\u0026rsquo;s ticket for the rollercoaster ride into sedimentary rock was usually an oxidizing agent that made it more soluble and better able to float, and\u0026nbsp;\u003Ca href=\u0022https:\/\/www.youtube.com\/watch?v=1O5yct7KAuw\u0022 rel=\u0022noopener noreferrer\u0022 target=\u0022_blank\u0022\u003Eatmospheric oxygen was an ideal oxidizer\u003C\/a\u003E. The chemical reaction,\u0026nbsp;\u003Ca href=\u0022https:\/\/doi.org\/10.1038\/s41467-017-01694-y\u0022 rel=\u0022noopener noreferrer\u0022 target=\u0022_blank\u0022\u003Ewhich can be found in the study\u003C\/a\u003E\u0026nbsp;and involved manganese oxide handing off oxygens to chromium, would be a little like adding pontoons to chromium compounds.\u003C\/p\u003E\r\n\r\n\u003Cp\u003EFor billions of years, Earth\u0026rsquo;s atmosphere was nearly devoid of O\u003Csub\u003E2\u003C\/sub\u003E, but after oxygen began increasing, especially\u0026nbsp;\u003Ca href=\u0022http:\/\/www.nature.com\/news\/2009\/090909\/full\/news.2009.901.html\u0022 rel=\u0022noopener noreferrer\u0022 target=\u0022_blank\u0022\u003Ein the last 800 million years\u003C\/a\u003E, \u0026nbsp;it became the domineering oxidizer. And characteristics of chromium deposits in ancient layers of rock became a great indicator of how much O\u003Csub\u003E2\u003C\/sub\u003E\u0026nbsp;was in the atmosphere.\u003C\/p\u003E\r\n\r\n\u003Cp\u003EToday, researchers test deep rock layer samples for the relation between two chromium isotopes,\u0026nbsp;\u003Ca href=\u0022https:\/\/www.webelements.com\/chromium\/isotopes.html\u0022 rel=\u0022noopener noreferrer\u0022 target=\u0022_blank\u0022\u003E\u003Csup\u003E52\u003C\/sup\u003ECr, by far the most common Cr isotope, and\u0026nbsp;\u003Csup\u003E53\u003C\/sup\u003E\u003C\/a\u003ECr, to get a read on oxygen presence\u0026nbsp;\u003Ca href=\u0022http:\/\/www.ucmp.berkeley.edu\/help\/timeform.php\u0022 rel=\u0022noopener noreferrer\u0022 target=\u0022_blank\u0022\u003Eacross geological eras\u003C\/a\u003E.\u003C\/p\u003E\r\n\r\n\u003Cp\u003E\u0026ldquo;You powder the rock up; you dissolve it with acid, and then you measure the ratio of\u0026nbsp;\u003Csup\u003E53\u003C\/sup\u003ECr to\u0026nbsp;\u003Csup\u003E52\u003C\/sup\u003ECr in the material by using mass spectrometry,\u0026rdquo; Reinhard said. \u0026ldquo;It\u0026rsquo;s the ratio that matters, and it will be controlled by a range of complex processes, but generally speaking, elevated\u0026nbsp;\u003Csup\u003E53\u003C\/sup\u003ECr in ocean sediment rock tends to indicate oxygen in the atmosphere.\u0026rdquo;\u003C\/p\u003E\r\n\r\n\u003Cp\u003EBy the way, these Cr isotopes are stable and don\u0026rsquo;t undergo radioactive decay, thus the system does not work the way\u0026nbsp;\u003Ca href=\u0022http:\/\/hyperphysics.phy-astr.gsu.edu\/hbase\/Nuclear\/cardat.html\u0022 rel=\u0022noopener noreferrer\u0022 target=\u0022_blank\u0022\u003Eradiocarbon dating\u003C\/a\u003Edoes, which relies on the decay of carbon 14.\u003C\/p\u003E\r\n\r\n\u003Ch4\u003E\u003Cstrong\u003EChemical imposter\u003C\/strong\u003E\u003C\/h4\u003E\r\n\r\n\u003Cp\u003EIn the lab, with a small assortment of organic ligands, Tang\u0026rsquo;s group showed that reactions of chromium with ligands led to\u0026nbsp;\u003Csup\u003E53\u003C\/sup\u003ECr\/\u003Csup\u003E52\u003C\/sup\u003ECr signals that closely mimicked those stemming from oxygen-chromium reactions.\u003C\/p\u003E\r\n\r\n\u003Cp\u003E\u0026ldquo;Ligands have the capability to mobilize chromium as well,\u0026rdquo; Tang said. \u0026ldquo;In fact, ligands might be a significant factor in controlling chromium isotope signals in certain rock records.\u0026rdquo;\u003C\/p\u003E\r\n\r\n\u003Cp\u003EOrganic ligands were probably around long before Earth\u0026rsquo;s atmosphere filled up with O\u003Csub\u003E2\u003C\/sub\u003E. And today, hundreds of millions of years after the reactions occurred, it\u0026rsquo;s basically impossible to find out if oxygen or ligands were at work.\u003C\/p\u003E\r\n\r\n\u003Ch4\u003E\u003Cstrong\u003ELittle discrepancies\u003C\/strong\u003E\u003C\/h4\u003E\r\n\r\n\u003Cp\u003EIf not accounted for, ligand reactions can distort small details in rock records about atmospheric oxygen, and they may have already.\u003C\/p\u003E\r\n\r\n\u003Cp\u003ELike paleontologists, who catalog ancient animal bones and other fossils, geologists keep\u0026nbsp;\u003Ca href=\u0022https:\/\/www.wired.com\/2010\/09\/the-nature-of-time-in-the-geologic-record\/\u0022 rel=\u0022noopener noreferrer\u0022 target=\u0022_blank\u0022\u003Emassive, digitized archives of rock that they study to learn more about Earth\u0026rsquo;s ancient geological history\u003C\/a\u003E. Scientists began testing physical samples of them with the Cr isotope system around 2009 and adding the results to the records.\u003C\/p\u003E\r\n\r\n\u003Cp\u003E\u0026ldquo;Since then, some discrepancies have turned up,\u0026rdquo; Reinhard said. \u0026ldquo;Ancient soil layers were showing evidence of oxygen when it probably shouldn\u0026rsquo;t have been there. Other samples from the same period weren\u0026rsquo;t showing that signal.\u0026rdquo;\u003C\/p\u003E\r\n\r\n\u003Cp\u003EBut some researchers confronted with odd Cr signals have thought they had perhaps stumbled upon a radical find, and they developed explanations for how O\u003Csub\u003E2\u003C\/sub\u003E\u0026nbsp;may have been surprisingly bountiful on the lonesome spot where a particular rock layer formed, while molecular oxygen was scant on the rest of the globe. Others puzzled that atmospheric O\u003Csub\u003E2\u003C\/sub\u003E\u0026nbsp;levels may have risen much earlier than overwhelmingly broad evidence has indicated.\u003C\/p\u003E\r\n\r\n\u003Cp\u003E\u0026ldquo;A lot of that could be chalked up to other chemical processes and not to interactions with oxygen,\u0026rdquo; Reinhard said.\u003C\/p\u003E\r\n\r\n\u003Cp\u003EThe study may serve as a cautionary tale about how to view Cr isotope data, especially when they leap off the page.\u0026nbsp;\u003C\/p\u003E\r\n\r\n\u003Cp\u003E\u003Ca href=\u0022http:\/\/www.rh.gatech.edu\/news\/555171\/animals-evolution-waited-eons-inhale\u0022 target=\u0022_blank\u0022\u003EAlso READ: Before Animals, Evolution \u003C\/a\u003E\u003Ca href=\u0022http:\/\/www.rh.gatech.edu\/news\/555171\/animals-evolution-waited-eons-inhale\u0022 target=\u0022_blank\u0022\u003EWaited\u003C\/a\u003E\u003Ca href=\u0022http:\/\/www.rh.gatech.edu\/news\/555171\/animals-evolution-waited-eons-inhale\u0022 target=\u0022_blank\u0022\u003E Eons to Inhale\u003C\/a\u003E\u003C\/p\u003E\r\n\r\n\u003Cp\u003E\u003Cem\u003EThe study was co-authored by Emily Saad from Georgia Tech, and Noah Planavsky and Xiangli Wang of Yale University. Research was funded by the NASA Astrobiology Institute (grant number\u0026nbsp;\u003C\/em\u003E\u003Cem\u003ENNA15BB03A, the NASA Exobiology program NNX16AL06G, and an Agouron Institute Postdoctoral Fellowship.\u003C\/em\u003E\u0026nbsp;\u003Cem\u003EAny opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of those sponsors.\u003C\/em\u003E\u003C\/p\u003E\r\n","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003EIf someone cries \u0026quot;Eureka!\u0026quot; because it looks like oxygen appeared in Earth\u0026#39;s ancient atmosphere long before the body of evidence indicates, consider this: If it was a chromium isotope system reading of ancient rock that caused the enthusiasm, it might need to be curbed.\u003C\/p\u003E\r\n","format":"limited_html"}],"field_summary_sentence":[{"value":"A system to determine the presence of ancient oxygen by testing rock layers may need to be taken with a grain of salt."}],"uid":"31759","created_gmt":"2017-11-15 19:25:23","changed_gmt":"2017-11-29 17:16:27","author":"Ben Brumfield","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2017-11-17T00:00:00-05:00","iso_date":"2017-11-17T00:00:00-05:00","tz":"America\/New_York"},"extras":[],"hg_media":{"598813":{"id":"598813","type":"image","title":"Pulverized rock in crucible","body":null,"created":"1510759829","gmt_created":"2017-11-15 15:30:29","changed":"1510759829","gmt_changed":"2017-11-15 15:30:29","alt":"","file":{"fid":"228290","name":"Biogemchem DSC_5327.jpg","image_path":"\/sites\/default\/files\/images\/Biogemchem%20DSC_5327.jpg","image_full_path":"http:\/\/www.tlwarc.hg.gatech.edu\/\/sites\/default\/files\/images\/Biogemchem%20DSC_5327.jpg","mime":"image\/jpeg","size":325742,"path_740":"http:\/\/www.tlwarc.hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/Biogemchem%20DSC_5327.jpg?itok=1sybpyFH"}},"598839":{"id":"598839","type":"image","title":"Yuanzhi Tang in her lab in Georgia Tech\u0027s School of Earth and Atmospheric Sciences","body":null,"created":"1510773216","gmt_created":"2017-11-15 19:13:36","changed":"1510773216","gmt_changed":"2017-11-15 19:13:36","alt":"","file":{"fid":"228309","name":"Biogemchem DSC_5381.jpg","image_path":"\/sites\/default\/files\/images\/Biogemchem%20DSC_5381.jpg","image_full_path":"http:\/\/www.tlwarc.hg.gatech.edu\/\/sites\/default\/files\/images\/Biogemchem%20DSC_5381.jpg","mime":"image\/jpeg","size":400073,"path_740":"http:\/\/www.tlwarc.hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/Biogemchem%20DSC_5381.jpg?itok=OHvkDwB7"}},"585306":{"id":"585306","type":"image","title":"Layered sedimentary rock","body":null,"created":"1482336114","gmt_created":"2016-12-21 16:01:54","changed":"1482336536","gmt_changed":"2016-12-21 16:08:56","alt":"","file":{"fid":"223155","name":"Photo 2.JPG","image_path":"\/sites\/default\/files\/images\/Photo%202.JPG","image_full_path":"http:\/\/www.tlwarc.hg.gatech.edu\/\/sites\/default\/files\/images\/Photo%202.JPG","mime":"image\/jpeg","size":972305,"path_740":"http:\/\/www.tlwarc.hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/Photo%202.JPG?itok=W2svUidE"}},"598837":{"id":"598837","type":"image","title":"Pouring pulverized rock from crucible ","body":null,"created":"1510772503","gmt_created":"2017-11-15 19:01:43","changed":"1510772503","gmt_changed":"2017-11-15 19:01:43","alt":"","file":{"fid":"228305","name":"Biogemchem DSC_5332.jpg","image_path":"\/sites\/default\/files\/images\/Biogemchem%20DSC_5332.jpg","image_full_path":"http:\/\/www.tlwarc.hg.gatech.edu\/\/sites\/default\/files\/images\/Biogemchem%20DSC_5332.jpg","mime":"image\/jpeg","size":230010,"path_740":"http:\/\/www.tlwarc.hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/Biogemchem%20DSC_5332.jpg?itok=6ctjBDnK"}},"598833":{"id":"598833","type":"image","title":"Acid on pulverized rock","body":null,"created":"1510771794","gmt_created":"2017-11-15 18:49:54","changed":"1510771794","gmt_changed":"2017-11-15 18:49:54","alt":"","file":{"fid":"228304","name":"biogemchem DSC_5347.jpg","image_path":"\/sites\/default\/files\/images\/biogemchem%20DSC_5347.jpg","image_full_path":"http:\/\/www.tlwarc.hg.gatech.edu\/\/sites\/default\/files\/images\/biogemchem%20DSC_5347.jpg","mime":"image\/jpeg","size":295401,"path_740":"http:\/\/www.tlwarc.hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/biogemchem%20DSC_5347.jpg?itok=AUQRwM5Q"}},"598838":{"id":"598838","type":"image","title":"Chris Reinhard and Yuanzhi Tang","body":null,"created":"1510772804","gmt_created":"2017-11-15 19:06:44","changed":"1510772804","gmt_changed":"2017-11-15 19:06:44","alt":"","file":{"fid":"228308","name":"Biogemchem DSC_5398.jpg","image_path":"\/sites\/default\/files\/images\/Biogemchem%20DSC_5398.jpg","image_full_path":"http:\/\/www.tlwarc.hg.gatech.edu\/\/sites\/default\/files\/images\/Biogemchem%20DSC_5398.jpg","mime":"image\/jpeg","size":419720,"path_740":"http:\/\/www.tlwarc.hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/Biogemchem%20DSC_5398.jpg?itok=0TFODRHx"}}},"media_ids":["598813","598839","585306","598837","598833","598838"],"groups":[{"id":"1278","name":"College of Sciences"},{"id":"1214","name":"News Room"},{"id":"1188","name":"Research Horizons"}],"categories":[],"keywords":[],"core_research_areas":[{"id":"39441","name":"Bioengineering and Bioscience"}],"news_room_topics":[{"id":"71911","name":"Earth and Environment"},{"id":"71881","name":"Science and Technology"}],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cp\u003E\u003Cstrong\u003EGeorgia Institute of Technology\u003Cbr \/\u003E\r\n177 North Avenue\u003Cbr \/\u003E\r\nAtlanta, Georgia \u0026nbsp;30332-0181 \u0026nbsp;USA\u003C\/strong\u003E\u003C\/p\u003E\r\n\r\n\u003Cp\u003E\u003Cstrong\u003EWriter and Media Relations Contact\u003C\/strong\u003E: Ben Brumfield (404-660-1408)\u003C\/p\u003E\r\n","format":"limited_html"}],"email":["ben.brumfield@comm.gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}