Interstellar cloud
A large interstellar cloud may have caused the extinction of dinosaurs ClaudioVentrella/iStock

A thick interstellar cloud may have caused the dinosaurs to become extinct. Researchers say the Earth could have crossed paths with an interstellar cloud – a large clump of cosmic dust and gas – 66 million years ago, starving the planet of light and making it very cold. They theorise that this ultimately led the dinosaurs to extinction.

A study, due to be published in Gondwana Research, identified thick deposits of iridium in the Pacific Ocean; a hard silvery-metal which the scientists believe may have been deposited from an interstellar cloud. They say this cloud would have caused a 'Nebula Winter', as the cloud would have blocked out a majority of the sunlight, which may have cooled the planet enough to kill most life.

The Earth is known to be covered in a blanket of iridium, roughly 30cm thick. This is believed to be caused by asteroid impacts. However, a team of scientists from the Japan Spaceguard Association found a section of the Earth's surface with a 5-metre thick layer of iridium. They say a layer this thick cannot be explained by an asteroid.

Where did the iridium come from?

The researchers suggest an alternative theory. They say this large abundance of iridium must have come from a specialised extra-terrestrial source, possibly an interstellar cloud.

Dinosaurs may have become extinct from a giant interstellar cloud Reuters

They suggest the interstellar cloud was more than 330 light-years across, and a thousand times more dense than space itself. It may have taken up to one million years for Earth to pass through the cloud, collecting a large amount of iridium from it at the same time.

The cloud would have blocked out sunlight, and caused the Earth to become very dark, reducing the amount of plant life. The planet would also become very cold from the icy cosmic dust. This may have been cold enough to wipe out the dinosaurs.

The scientists do not dispute the theory that a large asteroid struck the planet 66 million years ago; which is the more common understanding for the extinction of dinosaurs. They suggest it happened as well as the Earth passing through the molecular cloud. However, it was the cloud that was the primary factor in the dinosaurs extinction, they say.

The scientists say finding more space-originating radioactive elements will further strengthen their theory. In large amounts, these elements must have been left by a similar extra-terrestrial source. That could well be from the same interstellar cloud.