Estimated time for the recovery of coral reef ecosystems from human-caused ocean acidification; a similar time was taken for the recovery of marine ecosystems after the acidification event that occurred about 65 million years ago . The Grand Canyon will erode further, deepening slightly, but principally widening into a broad valley surrounding the Colorado River. 2.7 million, Average orbital half-life of current centaurs, that are unstable because of gravitational interaction of the several outer planets.