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We found the world's oldest asteroid strike in Western Australia. It might have triggered a global thaw – The Conversation AU

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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?




Read more:
Target Earth: how asteroids made an impact on Australia


How to date an asteroid hit

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.




Read more:
Ancient asteroid impacts yield evidence for the nature of the early Earth


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.

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Here’s how Helene and other storms dumped a whopping 40 trillion gallons of rain on the South

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More than 40 trillion gallons of rain drenched the Southeast United States in the last week from Hurricane Helene and a run-of-the-mill rainstorm that sloshed in ahead of it — an unheard of amount of water that has stunned experts.

That’s enough to fill the Dallas Cowboys’ stadium 51,000 times, or Lake Tahoe just once. If it was concentrated just on the state of North Carolina that much water would be 3.5 feet deep (more than 1 meter). It’s enough to fill more than 60 million Olympic-size swimming pools.

“That’s an astronomical amount of precipitation,” said Ed Clark, head of the National Oceanic and Atmospheric Administration’s National Water Center in Tuscaloosa, Alabama. “I have not seen something in my 25 years of working at the weather service that is this geographically large of an extent and the sheer volume of water that fell from the sky.”

The flood damage from the rain is apocalyptic, meteorologists said. More than 100 people are dead, according to officials.

Private meteorologist Ryan Maue, a former NOAA chief scientist, calculated the amount of rain, using precipitation measurements made in 2.5-mile-by-2.5 mile grids as measured by satellites and ground observations. He came up with 40 trillion gallons through Sunday for the eastern United States, with 20 trillion gallons of that hitting just Georgia, Tennessee, the Carolinas and Florida from Hurricane Helene.

Clark did the calculations independently and said the 40 trillion gallon figure (151 trillion liters) is about right and, if anything, conservative. Maue said maybe 1 to 2 trillion more gallons of rain had fallen, much if it in Virginia, since his calculations.

Clark, who spends much of his work on issues of shrinking western water supplies, said to put the amount of rain in perspective, it’s more than twice the combined amount of water stored by two key Colorado River basin reservoirs: Lake Powell and Lake Mead.

Several meteorologists said this was a combination of two, maybe three storm systems. Before Helene struck, rain had fallen heavily for days because a low pressure system had “cut off” from the jet stream — which moves weather systems along west to east — and stalled over the Southeast. That funneled plenty of warm water from the Gulf of Mexico. And a storm that fell just short of named status parked along North Carolina’s Atlantic coast, dumping as much as 20 inches of rain, said North Carolina state climatologist Kathie Dello.

Then add Helene, one of the largest storms in the last couple decades and one that held plenty of rain because it was young and moved fast before it hit the Appalachians, said University of Albany hurricane expert Kristen Corbosiero.

“It was not just a perfect storm, but it was a combination of multiple storms that that led to the enormous amount of rain,” Maue said. “That collected at high elevation, we’re talking 3,000 to 6000 feet. And when you drop trillions of gallons on a mountain, that has to go down.”

The fact that these storms hit the mountains made everything worse, and not just because of runoff. The interaction between the mountains and the storm systems wrings more moisture out of the air, Clark, Maue and Corbosiero said.

North Carolina weather officials said their top measurement total was 31.33 inches in the tiny town of Busick. Mount Mitchell also got more than 2 feet of rainfall.

Before 2017’s Hurricane Harvey, “I said to our colleagues, you know, I never thought in my career that we would measure rainfall in feet,” Clark said. “And after Harvey, Florence, the more isolated events in eastern Kentucky, portions of South Dakota. We’re seeing events year in and year out where we are measuring rainfall in feet.”

Storms are getting wetter as the climate change s, said Corbosiero and Dello. A basic law of physics says the air holds nearly 4% more moisture for every degree Fahrenheit warmer (7% for every degree Celsius) and the world has warmed more than 2 degrees (1.2 degrees Celsius) since pre-industrial times.

Corbosiero said meteorologists are vigorously debating how much of Helene is due to worsening climate change and how much is random.

For Dello, the “fingerprints of climate change” were clear.

“We’ve seen tropical storm impacts in western North Carolina. But these storms are wetter and these storms are warmer. And there would have been a time when a tropical storm would have been heading toward North Carolina and would have caused some rain and some damage, but not apocalyptic destruction. ”

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Follow AP’s climate coverage at https://apnews.com/hub/climate

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Follow Seth Borenstein on Twitter at @borenbears

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Associated Press climate and environmental coverage receives support from several private foundations. See more about AP’s climate initiative here. The AP is solely responsible for all content.

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‘Big Sam’: Paleontologists unearth giant skull of Pachyrhinosaurus in Alberta

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It’s a dinosaur that roamed Alberta’s badlands more than 70 million years ago, sporting a big, bumpy, bony head the size of a baby elephant.

On Wednesday, paleontologists near Grande Prairie pulled its 272-kilogram skull from the ground.

They call it “Big Sam.”

The adult Pachyrhinosaurus is the second plant-eating dinosaur to be unearthed from a dense bonebed belonging to a herd that died together on the edge of a valley that now sits 450 kilometres northwest of Edmonton.

It didn’t die alone.

“We have hundreds of juvenile bones in the bonebed, so we know that there are many babies and some adults among all of the big adults,” Emily Bamforth, a paleontologist with the nearby Philip J. Currie Dinosaur Museum, said in an interview on the way to the dig site.

She described the horned Pachyrhinosaurus as “the smaller, older cousin of the triceratops.”

“This species of dinosaur is endemic to the Grand Prairie area, so it’s found here and nowhere else in the world. They are … kind of about the size of an Indian elephant and a rhino,” she added.

The head alone, she said, is about the size of a baby elephant.

The discovery was a long time coming.

The bonebed was first discovered by a high school teacher out for a walk about 50 years ago. It took the teacher a decade to get anyone from southern Alberta to come to take a look.

“At the time, sort of in the ’70s and ’80s, paleontology in northern Alberta was virtually unknown,” said Bamforth.

When paleontogists eventually got to the site, Bamforth said, they learned “it’s actually one of the densest dinosaur bonebeds in North America.”

“It contains about 100 to 300 bones per square metre,” she said.

Paleontologists have been at the site sporadically ever since, combing through bones belonging to turtles, dinosaurs and lizards. Sixteen years ago, they discovered a large skull of an approximately 30-year-old Pachyrhinosaurus, which is now at the museum.

About a year ago, they found the second adult: Big Sam.

Bamforth said both dinosaurs are believed to have been the elders in the herd.

“Their distinguishing feature is that, instead of having a horn on their nose like a triceratops, they had this big, bony bump called a boss. And they have big, bony bumps over their eyes as well,” she said.

“It makes them look a little strange. It’s the one dinosaur that if you find it, it’s the only possible thing it can be.”

The genders of the two adults are unknown.

Bamforth said the extraction was difficult because Big Sam was intertwined in a cluster of about 300 other bones.

The skull was found upside down, “as if the animal was lying on its back,” but was well preserved, she said.

She said the excavation process involved putting plaster on the skull and wooden planks around if for stability. From there, it was lifted out — very carefully — with a crane, and was to be shipped on a trolley to the museum for study.

“I have extracted skulls in the past. This is probably the biggest one I’ve ever done though,” said Bamforth.

“It’s pretty exciting.”

This report by The Canadian Press was first published Sept. 25, 2024.

The Canadian Press. All rights reserved.

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The ancient jar smashed by a 4-year-old is back on display at an Israeli museum after repair

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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.”

The Canadian Press. All rights reserved.

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