At first glimpse it was just a black rock bound up in some mallee roots, found while clearing land in 2015.
But the roughly-spherical stone, known as a tektite and weighing 246.7 grams, tells an astonishing story of how it came to be buried in the dirt near Lake Yaninee between Wudinna and Minnipa on the Eyre Peninsula.
Tektites are solidified pieces of molten glass, thrown up by meteorite or asteroid impacts that melt the ground where they hit the Earth.
And the impact that threw up this one, was a doozy indeed –the tektite was found about 7000km from ground zero
“We don’t know exactly where the impact site is,” geologist Kieran Meaney (pictured above) said. “But we suspect it is somewhere near Vietnam.
“I think it was probably offshore, and that’s why we can’ t find it. There is a lot of debate about it.”
Some proposed sites for the now hidden crater include the Gulf of Tonkin off the coast of Vietnam, in Laos under the Bolaven volcanic field, or under the dunes of the Badain Jaran Desert in northwest China.
Dr Meaney, who is the South Australian Museum’s Assistant Collection Manager, Mineralogy, said debris from the impact now covered 20 percent of the world’s surface, from India, China, the Philippines, Indonesia to Australia.
Micro-tektites from this event have even been found in Antarctica.
In fact, the vast majority of the tektites found in Australia are from that single impact. This particular tektite is the third largest ever found in Australia, and is 10 to 20 times larger than most others that travelled that far from the same impact.
So, do we know when it happened?
“Yes … 788,000 years ago,” Dr Meaney said. “The radioactive elements in the glass have been dated and give a very precise age. Those elements are trapped when the molten glass solidifies, and that would have happened within minutes of the impact.”
The glass was formed from molten silica – Dr Meaney thinks the impact occurred on wet sand, which melts easily.
The tektite’s odd shape was forged by its journey to the edge of the Earth’s atmosphere and back.
Friction with the air as it fell formed a roughly equatorial ridge as one side was burned away as it fell.
While so much is known about the tektite and the impact, many mysteries remain, apart from the fact we can’t find where it happened.
“To our knowledge there wasn’t a significant disruption to climate caused by this impact,” Dr Meaney said. “This impact occurred in an ice age, so the cooling it caused may not have been a major disruption.”
Which is strange - other major impacts have caused climate chaos and major extinctions, such as the impact 65 million years ago near Mexico which is believed to have sparked the demise of dinosaurs.
For now at least, the tektite’s journey has come to an end -it was donated to the South Australian Museum last month (August) by tektite collector Aubrey Whymark.
Despite its incredible size and remarkable origin story, the tektite so far does not have a fancy name like other notable rocks and minerals in the South Australian Museum’s collection.
For example, meteorites are named for the location they were found, such as the Karoonda or Henbury meteorites. Other specimens get named for their outstanding quality, such as the Fire of Australia opal.
All of these specimens are on display in the Museum’s minerals gallery.
Does Dr Meaney have any naming suggestions for our newest tektite?
“Well, it’s affectionately known as T2279 to me,” they said.
The South Australian Museum has an extensive Mineral Sciences Collection on display.
For more information, visit the Museum’s website.
