Oxygenis the third most abundant element in the existence and establish up almost 21 % of Earth ’s air . It ’s hard to envisage a human beings without it , but other Earth was very dissimilar to how it is now . Until around2.45 billion years ago , the atmosphere was devoid of oxygen . However , investigator powerfully believed that thebiological productionof atomic number 8 began long before that , some 2.7 to 2.8 billion years ago , meaning that there was a significant gap between the first atomic number 8 - producing being and the “ Great Oxidation Event ” that flooded the oceans and atmosphere with oxygen .

Prior to the evolution of photosynthetic organisms , naive bug wereanaerobic , mean that they flourish in this absence of oxygen . However , there was grounds to hint that before oxygen became abundant , there were small “ oases ” of oxygen - productive water system , get by early microbes .

This idea was fuelled by thediscoveryof ancient rocks , dating between 4 to 2.5 billion year ago , that demonstrated band of iron - rich minerals . It is recall that these may have shape when microorganisms begin pump out oxygen which reacted with dismiss branding iron in saltwater , producing atom that were then deposited on the seabed .

Scientists therefore propose that oxygen may have first start pile up in this hostile populace in isolated pockets . “ The musical theme of atomic number 8 oases in ancient sea has been around for a long clock time , but no one was able-bodied to nail a specific example of such an oasis , ” Robert Riding toldNew Scientist . Now , Riding and colleagues conceive that they have identified an early example of a marine oxygen oasis , representing the first convincing grounds of these ancient pockets . The study has been put out inPrecambrian Research .

For the sketch , the squad collected 2.8 billion year old shallow - devil dog limestones and deep - H2O iron - rich sediment from Steep Rock Lake , Canada . According to Riding , these rocks are amongst the oldest and best preserved on Earth and accordingly have not changed much since they were laid down . The rocks in this locating also containstromatoliteswhich are layered anatomical structure of sedimentary tilt formed by flatness of microbes , in particular cyanobacteria .

The scientists examine the composition of the rock ‘n’ roll usingrare earth element analysesand notice that the seawater , from which the shallow - body of water limestones fall , was oxygenise . In demarcation , the nearby deeper waters that were home to iron - rich sediments were not oxygenated .

These findings were critical pieces of evidence given the fact that the main element of limestone , atomic number 20 carbonate , can only form in water destitute of dissolved iron . The team therefore suggest that the production of limestone was facilitate by bug pumping out atomic number 8 , which when reacted with the Fe in the seawater .

The oasis only lasted for around5 million year , however , because grow ocean levels oversupply the area with a smart provision of branding iron , bringing oxygen layer back down once again .

make its highly reactive nature , the oxygen in the oases would have actually beenharmfulto the anaerobic germ . This would have therefore driven the evolution of defense lawyers mechanisms that finally gave hike to organisms that could not only survive in oxygen rich surround , but also rein it to develop free energy , making a major transition in life on Earth .

[ ViaNew Scientist ]

[ Header range , " Limestone Quarry Cave & Lake # 3 " by Brent Moore , via Flickr , used in accordance of rights with   CC BY - NC 2.0 ]