T. rex and the Crater of Doom�is under copyright, but the�ebook can be purchased for�Kindle�or�Nook, and can be�downloaded from Google books.

You can also access the original scholarly article, co-authored by Walter Alvarez, his father Luis W. Alvarez, Helen V. Michel, and Frank Asaro,�here�and�here.

Go back to�the main Story of Science page.