WASHINGTON, April 11 (Xinhua) -- New geological evidence indicates that the Grand Canyon in the United States may be so old that dinosaurs once lumbered along its rim, according to a study by a team of U.S. researchers.

    The team from the University of Colorado and the California Institute of Technology used a technique known as radiometric dating to show the Grand Canyon may have formed more than 55 million years ago, pushing back its assumed origins by 40 million to 50 million years.

    The new study challenged the long-held belief that the Grand Canyon was carved by the Colorado River about 6 million years ago.

    The researchers gathered evidence from rocks in the canyon and on surrounding plateaus that were deposited near sea level several hundred million years ago before the region uplifted and eroded to form the canyon.

    A paper on the subject will be published in the May issue of the Geological Society of America Bulletin, according to a statement released by the University of Colorado.

    The team believes that an ancestral Grand Canyon developed in its eastern section about 55 million years ago, later linking with other segments that had evolved separately. "It's a complicated picture because different segments of the canyon appear to have evolved at different times and subsequently were integrated," said lead author Rebecca Flowers.