The world’s oldest remaining asteroid crater is at a place called Yarrabubba, southeast of the town of Meekatharra in Western Australia.
Our new study puts a precise age on the cataclysmic impact – showing Yarrabubba is the oldest known crater and dating it at the right time to trigger the end of an ancient glacial period and the warming of the entire planet.
What we found at Yarrabubba
Yarrrabubba holds the eroded remnants of a crater 70 kilometres wide that was first described in 2003, based on minerals at the site that showed unique signs of impact. But its true age was not known.
The Yarrabubba crater is about 70 kilometres across.
We studied tiny “impact-shocked” crystals found at the site, which show the crater formed 2.229 billion years ago (give or take 5 million years).
This new, precise date establishes Yarrabubba as the oldest recognised impact structure on Earth. It is some 200 million years older than the next oldest, the Vredefort impact in South Africa.
More intriguing, the geological record shows the Earth had glacial ice before the time of the impact – but afterwards, ice disappeared for hundreds of millions of years. Was the Yarrabubba impact a trigger for global climate change?
An asteroid strike is one of the most violent geologic events. In an instant, Earth’s crust is squeezed to unimaginable pressures, before exploding and ejecting carnage across the landscape. Large impacts leave behind scars the size of a small city.
The basin formed by an impact will partly fill with molten and pulverised rock from the Earth and from the asteroid itself. The edge of the crater forms a ring of mountains; over time erosion gradually erases the story.
Today, Yarrabubba has been worn down into a minor feature on a barren landscape.
To place the Yarrabubba event in a geologic context, we had to find its age. To find the age, we had to look carefully at minerals in the rocks shocked by the impact.
Geologists date events using “isotopic clocks” in minerals like zircon and monazite. These minerals contain small amounts of uranium, which gradually decays into lead at a known rate.
A shocked zircon crystal used to date the Yarrabubba impact. The margin (pink) recrystallised during impact, leaving the inner core (blue) intact. Scale bar is 80 micrometres, the width of human hair. Author provided
Asteroid strikes raise the temperature in rocks they hit, causing minerals to lose their accumulated lead, which resets the clock. After impact, the isotopic clocks start ticking again as new lead accumulates.
So by measuring the isotopes of uranium and lead in these minerals, we can calculate how much time has passed since the impact.
At Yarrabubba, we identified tiny crystals of zircon and monazite – each about the width of human hair – with textures that show they had been heated by a massive impact.
We analysed the amounts of lead and uranium isotopes in these crystals using mass spectrometry, and found their clocks had been reset 2.229 billion years ago (give or take five million years). That’s when we realised Yarrabubba coincided with a major change in Earth’s climate.
A different Earth
The Yarrabubba impact occurred during a period in Earth’s history called the Proterozoic eon. Long before plants, fish, or dinosaurs, life at this time consisted of simple, multicellular organisms.
These simple bacteria had already begun changing the composition of air. Previously dominated by carbon dioxide and methane, Earth’s atmosphere gradually became oxygenated by life about 2.4 billion years ago.
As oxygen levels built up, rocks started weathering more, and the atmosphere cooled down. And then ice came, plunging Earth into globally frigid conditions.
Earth has repeatedly dipped into glacial conditions over the last 4.5 billion years. We know about these periods because of deposits of solidified rock and mud that were ground up by glaciers as they bulldozed across Earth’s surface.
Studies have found multiple periods in Earth’s history in which glacial deposits occur in rocks of the same age across many continents. These deposits may represent worldwide glacial conditions, often referred to as a “Snowball Earth” event.
In these periods, ice forms from the poles well into the tropics, covering nearly all of Earth.
There is geological evidence that Earth was in an icy phase during the Yarrabubba impact. Rocks in South Africa show that glaciers were present at this time. But it’s not clear if the amount of ice was similar to today, or if it covered the world.
Fire and ice
So we found Earth’s oldest preserved impact crater, and worked out when the asteroid hit. We also know Earth had ice at the time, but not how much.
To understand the effect of the impact on an ice-covered world, we used computer models based on the physics of shockwaves to estimate how much ice would end up in the atmosphere as water vapour. As it turns out, it’s quite a lot.
Our models show that if the Yarrabubba asteroid hit an ice sheet 5 kilometres thick (not an unreasonable estimate), more than 200 billion tons of water vapour would be ejected into the atmosphere. That’s about 2% of the total amount of water vapour in today’s atmosphere, but would have been a much bigger fraction back then.
Water vapour is a serious greenhouse gas. It’s responsible for about half of the heat absorption from solar radiation today.
Global climate models don’t yet exist for the Proterozoic Earth, so we don’t yet know for sure if the Yarrabubba impact pushed the planet past a tipping point that led to more warming and the end of a possible Snowball Earth.
NAIROBI, Kenya (AP) — The body of Ugandan Olympic athlete Rebecca Cheptegei — who died after being set on fire by her partner in Kenya — was received Friday by family and anti-femicide crusaders, ahead of her burial a day later.
Cheptegei’s family met with dozens of activists Friday who had marched to the Moi Teaching and Referral Hospital’s morgue in the western city of Eldoret while chanting anti-femicide slogans.
She is the fourth female athlete to have been killed by her partner in Kenya in yet another case of gender-based violence in recent years.
Viola Cheptoo, the founder of Tirop Angels – an organization that was formed in honor of athlete Agnes Tirop, who was stabbed to death in 2021, said stakeholders need to ensure this is the last death of an athlete due to gender-based violence.
“We are here to say that enough is enough, we are tired of burying our sisters due to GBV,” she said.
It was a somber mood at the morgue as athletes and family members viewed Cheptegei’s body which sustained 80% of burns after she was doused with gasoline by her partner Dickson Ndiema. Ndiema sustained 30% burns on his body and later succumbed.
Ndiema and Cheptegei were said to have quarreled over a piece of land that the athlete bought in Kenya, according to a report filed by the local chief.
Cheptegei competed in the women’s marathon at the Paris Olympics less than a month before the attack. She finished in 44th place.
Cheptegei’s father, Joseph, said that the body will make a brief stop at their home in the Endebess area before proceeding to Bukwo in eastern Uganda for a night vigil and burial on Saturday.
“We are in the final part of giving my daughter the last respect,” a visibly distraught Joseph said.
He told reporters last week that Ndiema was stalking and threatening Cheptegei and the family had informed police.
Four in 10 women or an estimated 41% of dating or married Kenyan women have experienced physical or sexual violence perpetrated by their current or most recent partner, according to the Kenya Demographic and Health Survey 2022.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
VICTORIA – The British Columbia government is partnering with a bear welfare group to reduce the number of bears being euthanized in the province.
Nicholas Scapillati, executive director of Grizzly Bear Foundation, said Monday that it comes after months-long discussions with the province on how to protect bears, with the goal to give the animals a “better and second chance at life in the wild.”
Scapillati said what’s exciting about the project is that the government is open to working with outside experts and the public.
“So, they’ll be working through Indigenous knowledge and scientific understanding, bringing in the latest techniques and training expertise from leading experts,” he said in an interview.
B.C. government data show conservation officers destroyed 603 black bears and 23 grizzly bears in 2023, while 154 black bears were killed by officers in the first six months of this year.
Scapillati said the group will publish a report with recommendations by next spring, while an independent oversight committee will be set up to review all bear encounters with conservation officers to provide advice to the government.
Environment Minister George Heyman said in a statement that they are looking for new ways to ensure conservation officers “have the trust of the communities they serve,” and the panel will make recommendations to enhance officer training and improve policies.
Lesley Fox, with the wildlife protection group The Fur-Bearers, said they’ve been calling for such a committee for decades.
“This move demonstrates the government is listening,” said Fox. “I suspect, because of the impending election, their listening skills are potentially a little sharper than they normally are.”
Fox said the partnership came from “a place of long frustration” as provincial conservation officers kill more than 500 black bears every year on average, and the public is “no longer tolerating this kind of approach.”
“I think that the conservation officer service and the B.C. government are aware they need to change, and certainly the public has been asking for it,” said Fox.
Fox said there’s a lot of optimism about the new partnership, but, as with any government, there will likely be a lot of red tape to get through.
“I think speed is going to be important, whether or not the committee has the ability to make change and make change relatively quickly without having to study an issue to death, ” said Fox.
This report by The Canadian Press was first published Sept. 9, 2024.
