when did the colorado river start to form the grand canyon
Grand Canyon Nearly two billion years of Earth's geological history have been exposed as the Colorado River and its tributaries cut their channels through layer after layer of rock while the Colorado Plateau was uplifted.[4] While some aspects about the history of incision of the canyon are debated by geologists,[5] several recent studies support the hypothesis that the Colorado River established its course through the area about 5 to 6 million years ago.[1][6][7] Since that time, the Colorado River has driven the down-cutting of the tributaries and retreat of the cliffs, simultaneously deepening and widening the canyon.
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New France Thus, it extended from Newfoundland to the Canadian prairies and from Hudson Bay to the Gulf of Mexico, including all the Great Lakes of North America.
Colorado River Flows at the mouth of the river have steadily declined since the beginning of the 20th century, and in most years after 1960 the Colorado River has run dry before reaching the Pacific Ocean.[63] Irrigation, industrial, and municipal diversions, evaporation from reservoirs, natural runoff, and likely climate change, have all contributed to this substantial reduction in flow, threatening the water supply for the future.[64][65][66] For example, the Gila River – formerly one of the Colorado's largest tributaries – contributes little more than a trickle in most years due to use of its water by cities and farms in central Arizona.[67] The average flow rate of the Colorado at the northernmost point of the Mexico–United States border (NIB, or Northerly International Boundary) is about 2,060 cubic feet per second (58 m3/s), 1.49 million acre feet (1.84 km3) per year – less than a tenth of the natural flow – due to upstream water use.[68] Below this point, the remaining flow is diverted to irrigate the Mexicali Valley, leaving a dry riverbed from Morelos Dam to the sea that is supplemented by intermittent flows of irrigation drainage water.[69] There have been exceptions, however, namely in the early to mid-1980s, when the Colorado once again reached the sea during several consecutive years of record-breaking precipitation and snowmelt.[70] In 1984, so much excess runoff occurred that some 16.5 million acre feet (20.4 km3), or 22,860 cubic feet per second (647 m3/s), poured into the sea.[71]
Grand Canyon The Grand Canyon is part of the Colorado River basin which has developed over the past 70 million years,[12] in part based on apatite (U-Th)/He thermochronometry showing that Grand Canyon reached a depth near to the modern depth by 20 Ma.[13] A recent study examining caves near Grand Canyon places their origins beginning about 17 million years ago. Previous estimates had placed the age of the canyon at 5â€“6 million years.[14] The study, which was published in the journal Science in 2008, used uranium-lead dating to analyze calcite deposits found on the walls of nine caves throughout the canyon.[15] There is a substantial amount of controversy because this research suggests such a substantial departure from prior widely supported scientific consensus.[16] In December 2012, a study published in the journal Science claimed new tests had suggested the Grand Canyon could be as old as 70 million years.[17] However, this study has been criticized by those who support the "young canyon" age of around six million years as "[an] attempt to push the interpretation of their new data to their limits without consideration of the whole range of other geologic data sets."[14]