text: One thing you could do to get an idea of a reasonable minimum age is do tests to quantify erosion rates for moving water over various rock strata, then estimate how long it takes to cut out something like the grand canyon.  The age could of course be much more than this.\n\nAnother method might be to measure the depth of silt on the ocean floor.  Believe it takes about a thousand years to deposit one inch.  Again, just looking for a minimum.  Ice cores in Antarctica can also take you back millions of years by counting up the annual layers.