The Amazon river is the largest drainage system of rules in the world in terms of water volume and its drain basin . The 6,400 kilometer ( 4,000 mile ) river flow from the Andes Mountains of Peru , crossing South America before evacuate into the Atlantic Ocean . However , harmonize to a surprising find in 2006 and subsequent geologic study , that has not always been the case – millions of years in the past tense , the river flowed in the diametric commission .

Russell Mapes , then a graduate scholarly person geologist at the University of North Carolina , was attempting to investigate the flow of river sediment from the Andes Mountains all the way to the Atlantic Ocean , when he strike upon something really weird . search at aqueous deposit in the centre of South America , he found ancient pieces of the gemstone zircon , which could only have come from the easterly direction , rather than the immature Andes to the west .

“ All along the catchment area , the ages of the mineral grain point to very specific locating in central and eastern South America , " Mapes explained in astatementat the time .

That ’s unexpended , as the Amazon magnificently currently flows from West to East , not East to West . So what contribute these deposit of ancient zirconium silicate from the East to West ? This was n’t the only evidence that the river may have run in the diametrical direction , with fossils of maritime animate being that opt seawater being found in areas where it would n’t be expected that to happen .

appear into it further , the squad shape that the Amazon river reallydidflow in the opposite direction in the past . That team put the reversal down to a highland area in northeastern South America , which mold during the Cretaceous Period between 65 and 145 million year ago .

" The Amazon is so flat that a tilt in either direction can change thing drastically , ” Drew Coleman , Mapes ' executive program , explain .

They suggested that in a time before the Andes had formed , this slope make the river ( as it was then ) to run from East to West , towards the Purus Arch , while water on the west side of the archway flow towards the Pacific . accord to this team , as these upland areas in the nor'-east erode out , weewee begin to flow in the diametric direction . As the Andes grew , a basin formed between the mountains and the arch . Over time , this drainage area meet , before it eventually spill over , resulting in the counselling of flow we see today .

“ We think this last change befall within the past five to ten million year , which is really fast , geologically address , ” Mapes bring . “ This shows how transient the surface of the terra firma is . ”

While this was a reasonable hypothesis , alater model in 2014 suggestedthat the procession of the Andes caused them to intercept more clouds , and the subsequent flow of rainwater caused wearing , result in the Pebas wetlands . finally , on timescales which fit with the reversal around10 million years ago , sediment buildup prove the domain , resulting in the reversed flow of the Amazon river .

More study will hopefully slough light on the exact mechanism of the reversal , but the grounds show that the keen Amazon river once flowed in the opposite focussing .