An international scientific seafloor drilling project has drilled over 1500 deep holes in the past half century. The oldest seafloor sediments go to 220 million

An international scientific seafloor drilling project has drilled over 1500 deep holes in the past half century. The oldest seafloor sediments go to 220 million years. Anything older has been consumed by plate tectonics subduction. Scientists could count Pu244 in these cores to see how many nearby supernovae there were.