if you s it intoone pile, but is infinitesimal ingare exotic elements not normally muc iridium, in space t (because, it ist, most of to t was young).

    Alvarez kne a colleague of  tory in California,Frank Asaro, ecion of clays using a process called neutron activation analysis. trons in a small nuclear reactor and carefully counting t ted; it remely finicky tery, but Alvarez reasoned t if tof one of tic elements in  s annual rateof deposition, t aken to form. On an Octoberafternoon in 1977, Luis and alter Alvarez dropped in on Asaro and asked ests for them.

    It e a presumptuous request. to devote montomaking t painstaking measurements of geological samples merely to confirm irely self-evident to begin  ts ted. Certainly no one expected o yield any dramaticbreakthroughs.

    “ell, terview in 2002.

    “And it seemed an interesting co try. Unfortunately, I  of ot o it.” ed es from t 1:45 p.m.,  a sample in tector. It ran for 224minutes and ting interesting results, so opped it and had alook.”

    ts ed, in fact, t tists at first t tobe  of iridium in timesnormal levels—far beyond anyt ed. Over to ty  a stretcarted you couldn’t stop,” Asaro explained) analyzing samples, als.

    tests on otarctica—s t ly elevated every, and probablycataclysmic, ing spike.

    After muc, t t plausible explanation—plausible to t any rate— truck by an asteroid or comet.

    t t be subjected to devastating impacts from time to time quite as ne is noimes presented. As fa