The vast network of peaks within Grand Canyon represent a long and remarkable geologic history marked by erosion and deposition. The Grand Canyon's rock formation started in the early ages of our planet and the oldest rocks in this region date back to almost 2.5 billion years. These rocks are typically granite and schist. Once these rocks were formed, they were eroded over the next millions of years. About a billion years ago, the entire area was covered by the sea, and sediment was deposited along the canyon as the canyon's present day forms were eroded by water currents. The changes in sea level, alternate periods of deposition and erosion continued, till finally the sea receded. The Colorado river started its erosion very recently (a few million years ago) and we ended up with the current shape of Grand Canyon, studded with numerous peaks and deep valleys.
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