Cosmic proof of comet strike on Earth

[Image] An artist’s rendition of the comet exploding in Earth’s atmosphere above Egypt.
(Image: Wits University)

[Image] Professor David Block, was one of four astronomers who studied the Hypatia pebble.
(Image: David Block)

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Sulaiman Philip

“Let me remind the reader that everything that falls out of the sky always seems stranger than they actually are.” With these words, an anonymous reviewer on the esteemed science magazine Earth and Planetary Science Letters’ peer panel tried to dissuade the editor from publishing a collaborative paper written by a group of South African scientists.

Its significantly dry title – Unique chemistry of a diamond-bearing pebble from the Libyan Desert Glass-strewn field, SW Egypt: Evidence for a shocked comet fragment – obscures the importance of the work done by the group; Professors David Block and Jan Kramers, Chris Harris and Dr Marco Andreoli.

Comet strike proof

In a world-first, the work of these scientists, from the universities of the Witwatersrand, Johannesburg and Cape Town and the South African Nuclear Energy Corporation (NECSA) respectively, has provided the first concrete proof of a comet strike on Earth.

In a presentation at the University of the Witwatersrand, Professor Block explained that while comets have inspired fear and wonder throughout history, they are simply small dirty snowballs that “contain pristine material from the epoch of the formation of our solar system”.

“Comets always visit our skies … but never before in history has material from a comet ever been found on Earth.”

In the mid-1990s, during an expedition to the Libyan Desert, Egyptian geologist Ali Barakat picked up a black pebble that seemed out of place. Barakat’s curiosity was piqued because of its unusual streaked appearance and the lack of any similar rock formations in the debris field. Tests on the rock in Egypt showed that its composition was unusual but Barakat and his team could not tell just how much.

Barakat found the pebble in a 6000km2area of glass, believed to have been formed from a comet strike 28-million years ago. The comet heated the desert sands to almost 2 000 °C, creating a highly prized commodity, Libyan Desert glass, a fragment of which resides in a Pharaonic breast ornament belonging to boy king Tutankhamen.

A promising pebble

Barakat’s colleague, Dr Mario di Martino, called in Dr Andreoli to look at the rock because he believed the pebble may be a carbonado, but Andreoli was sceptical when his first round of tests results hinted that the pebble did not come from Earth.

Andreoli has spent his career studying carbonado rocks, better known as black diamonds. The high hydrogen content of these carbon rock formations and the fact that they are found in just two locations on Earth suggested to scientists that they were formed as result of comet impacts.

“Very early on I thought I was having a Narnia moment but I kept my emotions in check. It was only in 2011 when Professor Kramers’s anomalous results matched mine that I knew we had opened a new gate and a new door.”

What excited the team most were the microscopic diamonds in the rock’s core.  Diamonds are produced deep in the earth where intense pressure acts on coal. They are also formed by the high pressure shock caused by a comet explosion.

“Part of the comet impacted and the shock of the impact produced the diamonds,” says Kramers.

Microscopic dust particles and carbon-rich dust in Antarctic ice are the only comet material found on Earth. The North American Space Association (NASA) and the European Space Station spend billions of dollars to collect micrograms of comet material but “now we’ve got a radical new approach to studying the material without spending billions of dollars collecting it,” said Professor Kramers.

Professor Block added, “The pebble discovered in the field will help unlock, in the future, the secrets of the formation of our solar system.”

International interest

The team named their pebble Hypatia in honour of the first well-known female mathematician, astronomer and philosopher, Hypatia of Alexandria. As Dr Andreoli explained, “Comets are beautiful, mysterious bringers of life. To us Hypatia embodies all that. And we felt she deserved more than an asteroid and crater on the moon that no one knows how to find named after her.”

Comets differ from asteroids and meteors with their thin atmospheres and regular orbits and the bodies are even thought to have sparked life on Earth.

Hypatia’s importance lies in the fact that acts as a time capsule holding stardust from beyond our solar system.

The ongoing research and study of the pebble has grown to include scientists from around the world, including Italian scientists from the universities of Bologna and Turin.

For Professor Adam Habib, Wits vice-chancellor and principal, the fact that this significant discovery came as result of collaboration between South African universities was important.

He believes that ongoing collaboration would lead to more ground-breaking work in other fields and show the world the quality of South African tertiary institutions.

“If we want true freedom it can only be achieved when our minds are free. Work of this quality proves that we are on the road.”