The Cretaceous–Tertiary (K–T) mass extinction ~66 million years ago is believed to be the result of a massive impact.

Alvarez et al. [1] found strong evidence for the hypothesis that an extraterrestrial cause was responsible for this event. More recently, additional work points to an asteroid impact. Other possibilities would be a comet but also, as already discussed in their original publication by Alvarez et al., a supernova-explosion could be a possibility. These authors searched for a specific long-lived radionuclide, ²⁴⁴Pu, which has a half-life of 81 million years. Under the assumption that this nuclide is only produced in supernova explosions, its presence would be a clear indicator of a nearby supernova explosion. No ²⁴⁴Pu was detected at that time thus the authors concluded that a solar object was the most probable cause.

We have organised a sample from exactly the same region in Italy that was analysed by the authors and where they found for the first time enhanced iridium concentrations in a sedimentary layer. Within an international collaboration we have access to more material. Since the original work, ²⁴⁴Pu detection-sensitivity, however, has improved by more than a factor of a million. We will apply Accelerator Mass Spectrometry (AMS) for ²⁴⁴Pu measurements. AMS is the most sensitive technique for Pu analysis.

Within this project we will analyse a sample from this time period to exclude a supernova cause providing a much more stringent limit on extraterrestrial ²⁴⁴Pu influx.

[1] L.W. Alvarez et al., Extraterrestrial Cause for the Cretaceous-Tertiary Extinction, Science 208 (1980) 1095.