These humans survived a supervolcano
THE ground shook. The sky turned grey. The sea turned black.
The sun turned cold.
Imagine the scene in South Africa, 74,000 years ago.
Unknown to the inhabitants of Pinnacle Point, South Africa, a supervolcano, half-a-world away, had erupted.
It had unleashed a 800 cubic kilometre tsunami of magma on the island of Sumatra.
Ash falls circled the globe.
Now the night sky glowed a dull red. The air was full of a strange, harsh dust.
Summer did not come. Plants failed to bloom. The trees began to die.
Animals were starving.
Traces of this near-extinction event still show up in DNA today.
Estimates put the reduction of sunlight striking the Earth's surface at anywhere between 25 and 90 per cent.
Everywhere, there was ash. Among it was microscopic, hook-shaped fibres of glass - produced when tiny bubbles fracture.
Such fragments - with their unique identifying chemical composition - have turned up inancient rock shelters in South Africa.
And this has significant implications for a major theory of human evolution.
In recent decades anthropologists have argued the Toba supervolcano eruption, the biggest in the past two million years, produced an apocalyptic winter.
The skies were darkened for decades.
It was a worldwide catastrophe, they say, that drove humanity to the brink of extinction.
The theory goes that our species was reduced to a few thousand survivors, from which we all descend.
Researchers scoured ancient camps at Pinnacle Point on Mossel Bay and at a nearby cove for evidence of the Toba cataclysm.
They found its telltale traces of glass (cryptotephra) among the 40,000 excavated bones, tools and camp fires.
But these abundant signs of human habitation were found both above and below the supervolcano's cryptotephra fallout layer.
In fact, the population of the area actually grew.
"We showed that after the input of the shards, human occupation at the site actually increased dramatically," says Curtis Marean, from Arizona State University. "We never expected that."
And the dates of the settlements are clearly defined: the distinctive glass would have fallen from the skies within just a two-week period.
The cryptotephra layer also confirmed the optically stimulated luminescence (OSL) technique being developed by Zenobia Jacobs of the University of Wollongong, Australia.
This dates the last time individual grains of sand were last exposed to light.
"There has been some debate over the accuracy of OSL dating, but Jacobs' age model dated the layers where we found the Toba shards to about 74,000 years ago - right on the money," Marean says.
The Earth-shattering power of supervolcano eruptions has been inferred by the enormous extent of their lava flows, and the impact of the more recent - and much smaller - explosion of Mount Tambora in 1815.
This Indonesian produced what has become known as 'The Year Without Summer" in 1816. Crops failed in Europe, Asia and North America.
Famine was unleashed across the northern hemisphere.
The Toba supervolcano eruption would have dwarfed this.
Given the size and extent of its ash fall, it seems reasonable to believe its winter lasted for several years.
"Many previous studies have tried to test the hypothesis that Toba devastated human populations," Marean says. "But they have failed because they have been unable to present definitive evidence linking a human occupation to the exact moment of the event."
But the Pinnacle Point excavations are clearly concurrent to the supervolcano eruption.
Every sample was carefully recorded and chemically analysed.
And the story they tell is unexpected.
"These models tell us a lot about how people lived at the site and how their activities changed through time," says associate research scientist with the Institute of Human Origins Erich Fisher. "What we found was that during and after the time of the Toba eruption people lived at the site continuously, and there was no evidence that it impacted their daily lives."
At the very least, this study shows the inhabitants of the food-rich African coasts thrived through this apocalyptic time.
Further study is needed to determine if similar pockets of survivors were dotted around the world. Or if those who clung to life on this rocky headland represent the ancient origin of us all.