Discovery of Extraterrestrial 244Pu in 2 Million Year Old Fossilized Stromatolites
The rapid neutron capture process ( r -process) is responsible for producing about half of the elements heavier than iron in the Universe through cataclysmic events such as core-collapse supernovae and neutron star mergers (NSMs). Despite extensive research, the exact astrophysical sites of the r -p...
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| Main Authors: | , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2025-01-01
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| Series: | The Planetary Science Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/PSJ/adbbd6 |
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| Summary: | The rapid neutron capture process ( r -process) is responsible for producing about half of the elements heavier than iron in the Universe through cataclysmic events such as core-collapse supernovae and neutron star mergers (NSMs). Despite extensive research, the exact astrophysical sites of the r -process remain one of the unanswered questions in science. The well-known supernova-produced radioisotope ^60 Fe has been detected in terrestrial reservoirs, providing evidence that material from a nearby supernova reached Earth approximately 2 million years (Ma) ago. Our study reports the detection of ^244 Pu in fossilized stromatolite samples that are 2.0 Ma old, collected from palustrine–lacustrine stratigraphic layers dating back to approximately 5 Ma located at the margins of the present-day Lake Turkana Basin in northern Kenya. We demonstrate that stromatolites can mass-concentrate actinides in the range of 10 ^2 –10 ^3 . Using accelerator mass spectrometry, we isolate ^244 Pu and eliminate the anthropogenic contribution. From our findings, we evaluate a terrestrial fluence between 0.2 and 4.7 × 10 ^3 at cm ^−2 , in relative agreement with previous studies. The detection of the r -process ^244 Pu around 2 Ma ago raises the possibility of a common supernova origin with ^60 Fe; however, alternative scenarios, such as the production of ^244 Pu in NSMs or other cosmic events and its transport to Earth alongside ^60 Fe via interstellar debris, cannot be ruled out, highlighting the need to consider multiple mechanisms for isotopic transport in the cosmos. |
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| ISSN: | 2632-3338 |