what type of rock is at the bottom of the grand canyon
Geology of the Grand Canyon area At about 2.5 and 1.8 billion years ago in Precambrian time, sand, mud, silt, and ash were laid down in a marine basin adjacent to an orogenic belt.[1] From 1.8 to 1.6 billion years ago at least two island arcs collided with the proto-North American continent.[2] This process of plate tectonics compressed and grafted the marine sediments in the basin onto the mainland and uplifted them out of the sea. Later, these rocks were buried 12 miles (19 km) under the surface and pressure-cooked into metamorphic rock.[3] The resulting Granite Gorge Metamorphic Suite, which is part of the Vishnu Basement Rocks, consists of the metasedimentary Vishnu Schist and the metavolcanic Brahma and Rama Schists that were formed 1.75 billion to 1.73 billion years ago.[4] This is the resistant rock now exposed at the bottom of the canyon in the Inner Gorge.
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]
Grand Canyon James Ohio Pattie, along with a group of American trappers and mountain men, may have been the next European to reach the canyon, in 1826.[26]
Canyon The Grand Canyon of northern Arizona in the United States, with an average depth of 1,600 m (one mile) and a volume of 4.17Â trillion cubic metres,[7] is one of the world's largest canyons. It was among the 28 finalists of the New7Wonders of Nature worldwide poll. (Some referred to it as one of the 7 natural wonders of the world.[8]) Copper Canyon in Chihuahua, Mexico is deeper and longer than the Grand Canyon.