Gigantism in unique biogenic magnetite at the Paleocene–Eocene Thermal Maximum. 2008. Dirk Schumann et al. PNAS published ahead of print October 20, 2008.
From the press release:
Researchers have unearthed crystalline magnetic fossils of a previously unknown species of microorganism that lived at the boundary of the Paleocene and Eocene epochs, some 55 million years ago.
Though they are only some four microns long, these newly discovered, spear-shaped magnetite crystals (magnetofossils) – unearthed at a dig in New Jersey – are up to eight times larger than previously known magnetofossils. Magnetofossils are remnants of magnetite crystals produced by a type of bacteria called magnetotactic bacteria that are capable of orienting themselves along the direction of the Earth's magnetic field.
"Previous reports suggested that the source of the magnetic signature in the boundary layer was a type of magnetite that was formed by the impact of a comet," said lead researcher and corresponding author Dr. Hojatollah Vali. "In our previous paper we proved that the magnetic signature comes from biogenic material.
This species of microorganism, explained Vali, lived during a period of abrupt global warming known as the Paleocene-Eocene Thermal Maximum (PETM), when worldwide temperatures rose by 5° to 6° C over a period of 20,000 years.
