In 1980 such an idea was treated by paleontologists as supermarket tabloid stuff. Only the prestige of the four authors, Nobel laureate Luis Alvarez and three other respected scientists from Lawrence Berkeley Laboratory and the University of California at Berkeley, kept the paper from being ignored. Berkeley team's discovery Here is the story behind the development of the Berkeley team's research. Geologist Walter Alvarez, after returning from a field trip to Italy, mentioned to his father, Luis, his difficulty in coming up with a model to explain how a pencil-thin layer of gray clay at the top of the Cretaceous sediments may have been deposited. Luis suggested that Walter first measure the quantity of iridium in the clay to determine the time span over which the clay was deposited.
Iridium is an element of the platinum group.
Though relatively abundant in the earth's core and in certain kinds of meteorites, it is an extremely rare element in the outer crust of the earth. What little does exist in the earth's crust, Luis reasoned, must have come from meteorite dust. Assuming that the quantity of iridium being deposited at the Cretaceous period is approximately the same as it is now, a measure of the amount of iridium in any given sedimentary layer helps determine the time scale for the sedimentary process in forming that layer. The Berkeley team was shocked to discover that the amount of iridium in that clay layer exceeded by thirty times the amount that would be expected by even the slowest sedimentation imaginable. After the publication of the Berkeley team's paper, researchers found huge quantities of iridium worldwide in the top layer of Cretaceous deposits.