Ocean Floor: Australian scientists found highly radioactive isotopes – iron-60 and plutonium-240 – in high concentrations, 1,500 meters deep, at the bottom of the Pacific Ocean. These are chemical elements that are not present in nature, so they can only have come this far from outside our solar system. Its presence can now help to better understand the physics of cataclysmic events such as supernovae (stellar explosions) and perhaps even collisions of neutron stars.
Unstable elements under the sea
Many stars have already collided in the history of the universe, releasing iron, uranium, plutonium, gold and other heavy elements across the galaxy. The Earth is expected to have a good amount of these elements – some more stable than others.
But heavy elements like iron-60 are unstable, which means that, over time, they degrade into smaller, more stable atoms. That’s why we have a lot of nickel atoms in our terrestrial environment – they were once iron-60. But even before that: the element has a half-life (half the time it takes to decompose) of 2.6 million years, which for us is a lot, but in terms of the universe, it is little.
And then how are iron-60 isotopes found on the ocean floor? Where are they coming from, if it has already turned nickel around here? Iron-60 is commonly produced in supernova explosions, along with many other heavy elements – and some of them end up in our solar system. Then finding the element in high concentrations in the earth’s crust, isolated from artificial human processes, suggests to scientists an influx of the isotope into Earth’s geologically recent past.
The study team detected two peaks of iron-60 in the last 10 million years on our planet. Knowing that they are probably the result of nearby supernova explosions (within a few hundred light years), the team decided to see what other isotopes were present in the same areas of the ocean. That was when they discovered a small, but remarkable, amount of plutonium-244 – which has a half-life of 80 million years.