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A major extinction spasm is under way, threatening to eliminate millions of species. Fortunately we still have time—although only just—to slow and stem the tide of extinctions that is washing over earth's biotas. We cannot stop the mass extinction altogether; the processes of broad-scale habitat depletion have generated too much momentum to be halted overnight. But there is still much we can do to contain the scale of extinctions. In short, the prospect of a broad-scope depletion of earth's biodiversity is all too real: a profound problem. All too real also is the scope for an expansive effort to limit the phenomenon, and to save species in their millions: a splendid opportunity.