The crystal-clear waters of the Philippine archipelago, eerily empty of sea life...a lush Hawaiian paradise now the scene of devastating depopulation and extinction...the mighty Columbia River, stripped of its once abundant salmon, now an empty series of damned lakes...wolves, at one time numbering more than 2 million in the continental United States, now dwindled to perhaps 2,000.

Twice in the distant past, catastrophic extinctions have swept the earth, causing the "end" of evolution for certain creatures and the beginning for others. The first occurred 250 million years ago and marked the destruction of 90 percent of all living creatures - and the survival of our first mammalian ancestors.

The second great mass extinction took place 65 million years ago and 50 percent of all species - including the last of the dinosaurs - perished in a cataclysm that may have been caused in part by the earth's collision with an asteroid. Now Peter Ward, on a journey that traverses continents and travels into the past, searches for the clues to these disastrous events. His reason is urgent and chilling, for Ward and many other prominent scientists have documented signs that a third mass extinction has already begun on our planet.

Could its primary cause reach back just 100,000 years, when the earth felt the impact of another wandering, potentially destructive force, a new "asteroid" called Homo sapiens?

Ward's journey progresses from fossil hunting in Africa to following a dinosaur trail in Hell Creek, Montana, and finally to climbing high in the remote Caucasus Mountains of Soviet Georgia to see if its thick white limestone holds evidence of a long-ago planetary destruction. At each stop along the way, Ward documents the rich diversity of life now endangered by changes in climate and the world's burgeoning population.

In this rich, accessible book Ward gives us reason to marvel and mourn, fear and hope - and clearly demonstrates the urgency of the need to preserve life as we know it before our time runs out.