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Our experimental results are then compared with these estimations.
Based on a uniform production model, although of low statistical significance, supports the scenario of penetration of large ISD particles into the inner SS and may be consistent with the satellite data.
Such a process is confirmed by inclusion in these archives of meteoritic Fe (2.62 My), owing to their longer half-life).
Several models, based on the frequency of SN events, the nucleosynthesis yield and the radioactive half-life, were developed to calculate the abundance of Pu in quasi-secular equilibrium between production and radioactive decay rates.
The measured Pu particle flux using chemical yield, detection efficiency, the incorporation efficiency of Pu into the crust (21±5 %, see Methods and Table 3), and the area and time period covered.
We also assume that the extraterrestrial Pu flux through Earth’s cross-section is homogeneously distributed over the Earth’s surface.
If continuously produced, the Interstellar Medium is expected to build-up a quasi-steady state of abundances of short-lived nuclides (with half-lives ≤100 My), including actinides produced in r-process nucleosynthesis.
Their existence in today’s interstellar medium would serve as a radioactive clock and would establish that their production was recent.
In particular Pu, archived in Earth’s deep-sea floor during the last 25 My, at abundances lower than expected from continuous production in the Galaxy by about 2 orders of magnitude.
Extraterrestrial dust particles, cosmogenic nuclides and terrestrial input sink to the ocean floor and are eventually incorporated into the Fe Mn crust or sediment.
For actinide transport through the latter stages, the observed deposition of global fallout in deep marine reservoirs after injection to the stratosphere serves as a proxy to extraterrestrial particles.
Terrestrial archives like deep-sea Fe Mn crust and sediment archives extend over the past tens of million years.