Joe Carter asks how long would it take for all traces of humanity to disappear from the earth after humans went extinct. By way of an answer he links us to this graphic.
I suppose the graphic assumes that the extinction was caused by a natural loss of reproductive vitality, but the numbers would probably be different were the extinction caused by the effects of a large-scale nuclear war.
In any case the chart should give pause to those who sunnily assume that the meaning of anything we do here on earth is independent of whether there is an eternal destiny awaiting us. If there is not, if existence is transient, then whatever we accomplish, the graphic reminds us, is doomed ultimately to be reduced to nothing but overgrowth and decay. Our efforts only have meaning if our existence has permanence, and belief that our existence has permanence is a truly blind and irrational hope unless it is based on belief in the existence of God.