Other Research

Natural Quasicrystals

Quasicrystals are solids whose atomic arrangements have symmetries forbidden for periodic crystals, including configurations with five-fold symmetry. All examples identified to date have been synthesized in the laboratory under controlled conditions. Here we present evidence of a naturally-occurring icosahedral quasicrystal that includes six distinct five-fold symmetry axes. The mineral, an alloy of aluminum, copper and iron, occurs as micron-sized grains associated with crystalline khatyrkite and cupalite in samples from the Koryak mountains in Russia.

Incompleteness of the Fossil Record affects Biodiversity

The fossil record is clearly incomplete; the vast majority of organisms die without leaving a trace. But does this have any effect on the big picture of large-scale biodiversity, and how it changes through time? Motohiro Yogo, Charles R. Marshall and myself showed that indeed this incomplete preservation has significant effects. Earlier work suggested that, following a mass-extinction in which a lot of species were wiped out, it took a long time to recover back to a high level of biodiversity, due to an unexplained "speed limit" on recovery.

Peter J. Lu  |  Harvard University  |  Cambridge, MA 02138 USA |  plu_at_fas.harvard.edu