In a deep ocean ferromanganese crust an excess of radioactivity was measured by means of high sensitivity accelerator mass spectrometry. The enhanced concentrations measured in the first two of three layers (corresponding to a time span of 0–2.8 Myr and 3.7–5.9 Myr, respectively) suggest the deposition of supernova produced on earth. There is even a weak indication that the flux into the crust was higher about 5 Myr ago.
- Received 14 December 1998
©1999 American Physical Society