" we are pretty confident , " said t . mark harrison , a ucla geochemist and co - author of one of the studies . " two studies conducted independently apparently have come to the same conclusion . "我們相當(dāng)有把握, "研究之一的加州大學(xué)洛杉磯分校geochemist和合作研究者。 " t .馬克harrison說。二項(xiàng)單獨(dú)地指導(dǎo)的研究明顯得到相同的結(jié)論.