1·They had found, accidentally, that a rare metal, iridium, suddenly became very abundant exactly at the boundary and then slowly fell away.
他们偶然发现一种稀有金属铱的含量在边界处突然变得很丰富，然后又慢慢地消失了。
2·This sediment layer is enriched in the rare metal iridium and other elements that are relatively abundant in a meteorite but very rare in the crust of Earth.
这一沉积层富含稀有金属铱，以及其他在陨石中较丰富而在地壳中十分罕见的元素。
3·Debris thrown into the atmosphere by an asteroid collision would presumably contain large amounts of iridium, and atmospheric currents would carry this material all over the globe.
小行星碰撞后的碎片可能会含有大量的铱，而大气洋流会把这些物质带到全球各地。
4·Iridium occurs in meteorites and volcanic material, but in the latter case it is accompanied by elevated levels of nickel and chromium.
铱存在于陨石和火山物质中，但在火山物质中同时包含高浓度的镍和铬。
5·Indeed, two iridium layers have been found in some places.
事实上，在某些地方发现了两个铱岩层。