Researchers used extraterrestrial dust that settled on the ocean floor to measure the amount of heavy metals that are created in an explosion in space, and what they found could cause the nature of supernovae to be called into question.
The findings contradict current theories that look at how materials that are essential for human life (such as iron, potassium and iodine) are spread throughout the universe in supernovae explosions, Australian National University reported. The study could change the way scientists look at supernovae explosions.
"Small amounts of debris from these distant explosions fall on the earth as it travels through the galaxy," said lead researcher Anton Wallner, from the Research School of Physics and Engineering. "We've [analyzed] 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."
Supernovae also create lead, silver and gold, and heavier radioactive elements such as uranium and plutonium. The researchers studied plutonium-244 , which acts as a "radioactive clock" that has a half-life of 81 million years.
"Any plutonium-244 that existed when the earth formed from intergalactic gas and dust over four billion years ago has long since decayed," Wallner said. "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."
To make their findings, the researchers analyzed a 10 centimeter-thick sample of the earth's crust and found 100 times less plutonium-244 than they expected. This suggests some of the heaviest elements may not have been formed in a supernovae, but rather a rarer event such as the merging of two neutron stars. The fact that heavy elements like plutonium were detected, and uranium and thorium are still present on earth suggests an explosive event happened relatively close to the Earth.
"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," Wallner said.
The findings were published in a recent edition of the journal Nature Communications.
