About Luis Alvarez:
Luis Alvarez is a good example of how an "amateur" can have a profound impact on the world of paleontology. The word "amateur" is in quotation marks because, before he turned his attention to the extinction of the dinosaurs 65 million years ago, Alvarez was a highly accomplished physicist (in fact, he won the Nobel Prize in Physics in 1968 for his discovery of the "resonance states" of fundamental particles). He was also a lifelong inventor, and was responsible for (among other things) the Synchrotron, one of the first particle accelerators used to probe the ultimate constituents of matter.
In paleontology circles, though, Alvarez is best known for his late 1970's investigation (conducted with his geologist son, Walter) into the K/T Extinction, the mysterious event 65 million years ago that killed the dinosaurs, as well as their pterosaur and marine reptile cousins. His theory was that the impact of a large comet or meteor threw up tons of dust, blotted out the sun, and caused the earth’s vegetation to wither, with the result that plant-eating and then meat-eating dinosaurs starved and froze to death.
Alvarez's conclusion was greeted with skepticism at first, but is now accepted by the majority of scientists, especially after scattered iridium deposits in the vicinity of the Chicxulub meteor crater (in present-day Mexico) could be traced to the impact of a large interstellar object. Still, that hasn't prevented some scientists from pointing to ancillary causes for the extinction of the dinosaurs, the most likely candidate being the volcanic eruptions triggered when the Indian subcontinent slammed into the underside of Asia at the end of the Cretaceous period.