When a star reaches the end of its life, some of its mass flows into the core. When the core becomes dense enough it is torn apart by its own gravitational force. The core collapses and the star explodes, spreading the elements that makes it up though the galaxy.

The remnants of long since exploded stars can be found on Earth. They are, in fact, critical to life here. Recently scientists scoured stable areas of the sea floor, looking for the remnants of supernovae in the hope of learning more about the processes involved.

Meteors striking the Earth are the stuff of action movies and occasionally newscasts. In reality, meteors rain down on Earth constantly but most of these are not big enough to make the news. The vast majority of meteors range in size from a grain of rice to a speck of dust.

Using a cookie sheet, some plastic wrap, a magnet and a sheet of paper anyone can collect meteors in their back yard. It stands to reason that the oceans, which cover 70 percent of the planet, are good collectors of star stuff and space debris.

Researchers from the Australian National University (ANU) recently analyzed a 10 centimeter sample of the Earth’s crust, as well as sediments collected from the deep-sea to look for supernova elements.

“Small amounts of debris from these distant explosions fall on the earth as it travels through the galaxy. We’ve analysed galactic dust from the last 25 million years that has settled on the ocean and found there is much less of the heavy elements such as plutonium and uranium than we expected,” said lead researcher Dr Anton Wallner, from the Research School of Physics and Engineering at ANU, in a statement.

Among the elements released by supernovae are iron, potassium and iodine which are essential for human life. When Carl Sagan famously said “we are all star stuff,” this is what he meant. The remnants of exploding stars make up part of every human on Earth. The stars also release lead, silver, gold and the heavy radioactive elements plutonium and uranium.

Dr. Waller’s team specifically looked for plutionium-244 which has a half-life of 81 million years and can act as a clock, telling researchers how old it is.

“Any plutonium-244 that existed when the earth formed from intergalactic gas and dust over four billion years ago has long since decayed. So any plutonium-244 that we find on earth must have been created in explosive events that have occurred more recently, in the last few hundred million years,” said Dr. Wallner.

What Wallner’s team found may force researchers to reexamine what they know about exploding stars.

“We found 100 times less plutonium-244 than we expected. It seems that these heaviest elements may not be formed in standard supernovae after all. It may require rarer and more explosive events such as the merging of two neutron stars to make them,” ,” Dr Wallner said.

Based on the research Wallner believes that such an event must have happened close to the Earth shortly after the planet formed.

“Radioactive elements in our planet such as uranium and thorium provide much of the heat that drives continental movement, perhaps other planets don’t have the same heat engine inside them,” he said.

The results of the research can be found in the journal Nature Communications.