At the southern end of Madagascar lie four enormous wedge-shaped sediment deposits, called chevrons, that are composed of material from the ocean floor. Each covers more than 100 square kilometers with sediment hundreds of meters deep. On close inspection, the chevron deposits contain deep-ocean microfossils that are fused with a medley of metals typically formed by cosmic impacts. And all of them point in the same direction - toward the middle of the Indian Ocean where a newly discovered crater, 29 kilometers, or 18 miles, in diameter, lies 3,800 meters, or 12,500 feet, below the surface.