Some scientists believe we are now in the midst of another great extinction, driven not by natural events but by the activities of man: hunting, habitat destruction, the introduction of invasive species and pollution, which has drastically altered the thin glaze of life-supporting chemistry that coats the earth. By some estimates, perhaps close to 30,000 species of plants and animals go extinct every year. Whole ecosystems, like coral reefs, which went virtually extinct in the end-Triassic extinction, are now facing worldwide collapse again.

A World Bank report last fall warned that “present emission trends put the world plausibly on a path toward 4 degrees Celsius warming within the century.” The surface waters of the carbon-dioxide absorbing oceans have already become 30 percent more acidic since the start of the Industrial Revolution.

“In terms of global warming and ocean acidification,” Professor Olsen said, the rate of change during the end-Triassic extinction “was comparable to what we’re doing today.”

As I looked up the cliffs I wondered what we would leave to the ages. If catastrophe strikes, would future geologists find evidence of New York, a marker for our time, just as the Palisades have survived as a tombstone for another era?