Science

Asteroid that crashed into Earth 2 billion years ago was up to 15 miles across

Theory: An asteroid that crashed into Earth two billion years ago in what is now South Africa was even bigger than the one that wiped out the dinosaurs, new research suggests.  It left the Vredefort crater near present-day Johannesburg (pictured)
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An asteroid that struck Earth two billion years ago in what is now South Africa was even larger than the one that wiped out the dinosaurs, new research suggests.

Previous studies estimated that the planet’s largest crater was formed by an object about 15 km wide traveling at a speed of 33,500 mph (15 km/s).

But a new study disputes this, with experts suggesting the space rock was actually as much as 15 miles (24 km) wide.

Researchers at the University of Rochester say the asteroid impact that left Vredefort Crater near modern-day Johannesburg would have had devastating consequences across the planet.

They hope their study will allow scientists to better simulate impact events on Earth and other planets, both in the past and in the future.

Theory: An asteroid that crashed into Earth two billion years ago in what is now South Africa was even bigger than the one that wiped out the dinosaurs, new research suggests.  It left the Vredefort crater near present-day Johannesburg (pictured)

Theory: An asteroid that crashed into Earth two billion years ago in what is now South Africa was even bigger than the one that wiped out the dinosaurs, new research suggests. It left the Vredefort crater near present-day Johannesburg (pictured)

Previous studies estimated that the planet's largest crater was formed by an object about 15 km wide traveling at a speed of 33,500 mph (15 km/s).

Previous studies estimated that the planet’s largest crater was formed by an object about 15 km wide traveling at a speed of 33,500 mph (15 km/s).

THE VREDEFORT IMPACT CRATER

Two billion years ago, a giant space rock struck Earth about 62 miles (100 km) southwest of Johannesburg, creating the Vredefort impact crater.

The asteroid, larger than Table Mountain, caused an energy explosion of a thousand megatons. The impact would have vaporized about 70 cubic kilometers of rock. The heat from the impact was enough to melt the Earth’s crust and create a magma lake.

The world has about 130 crater structures with possible impact origin. The Vredefort Dome is one of the top 3 and is the oldest and largest clearly visible impact site in the world.

What remains of the event are impact-related rocks, composed of fractured mineral fragments that formed immediately after the impact.

“Understanding the largest impact structure we have on Earth is crucial,” said Natalie Allen, who is now a graduate student at Johns Hopkins University.

“Having access to the information provided by a structure like Vredefort Crater is a great opportunity to test our model and understanding of the geological evidence so we can better understand the impacts on Earth and beyond.”

Over the course of two billion years, the Vredefort crater has eroded.

This makes it difficult for scientists to directly estimate the size of the crater at the time of the initial impact, and thus the size and speed of the impactor that created the crater.

An object 15 km (9.3 miles) wide and traveling at 15 km/s (33,500 mph) would create a crater about 172 km (106 miles) in diameter.

However, this is much smaller than current estimates for Vredefort Crater.

These are based on new geological evidence and measurements that estimate the structure’s original diameter at the time of impact would have been between 155 and 174 miles (250 and 280 km).

Allen and her colleagues ran simulations to fit the updated size of the crater.

Their results showed that an impactor would have to be much larger – about 12 to 15 miles (20 to 25 km) – and traveling at a speed of 33,500 to 44,700 mph (15 to 20 km/s) to hit a 155 Miles (250 km) in size.

That means the space rock that formed Vredefort Crater would have been larger than the asteroid that killed the dinosaurs and formed Chicxulub Crater 66 million years ago.

These impacts had detrimental effects worldwide, including warming of greenhouses, widespread wildfires, acid rain, and depletion of the ozone layer, in addition to causing the Cretaceous-Paleogene extinctions that killed the dinosaurs.

If the Vredefort crater was even larger and the impact more energetic than that which formed the Chicxulub crater, the Vredefort impact might have caused even more catastrophic global consequences.

“Unlike the Chicxulub impact, the Vredefort impact left no record of mass extinctions or wildfires because two billion years ago there were only unicellular life forms and no trees existed,” said researcher Miki Nakajima.

“However, the impact might have affected global climate more comprehensively than the Chicxulub impact.”

Dust and aerosols from the Vredefort impact would have spread across the planet, blocking sunlight and cooling the Earth’s surface, she added.

“This could have had devastating effects on photosynthetic organisms.

“After the dust and aerosols settled — which could have taken hours to a decade — greenhouse gases such as cardoon dioxide released by the impact could have increased global temperature by several degrees, potentially over a long period of time.”

But a new study disputes this, with experts suggesting it was actually as much as 15 miles (24 km) wide.  The Vredefort Dome (pictured) is the oldest and largest clearly visible impact site in space in the world

But a new study disputes this, with experts suggesting it was actually as much as 15 miles (24 km) wide. The Vredefort Dome (pictured) is the oldest and largest clearly visible impact site in space in the world

Researchers from the University of Rochester say the asteroid impact would have had devastating consequences for the entire planet

Researchers from the University of Rochester say the asteroid impact would have had devastating consequences for the entire planet

The simulations also allowed researchers to study the material ejected by the impact and the distance the material traveled from the crater.

They can use this information to determine the geographic location of landmasses billions of years ago. For example, previous research found that material from the asteroid was ejected into what is now Karelia in Russia.

Using their model, the researchers determined that two billion years ago, the distance of the landmass containing Karelia would have been only 1,200 to 1,500 miles (2,000 to 2,500 km) from the crater in South Africa – much closer than the two areas are today.

“It’s incredibly difficult to pinpoint the location of landmasses long ago,” Allen said.

“The current best simulations are mapped back about a billion years, and the uncertainties get bigger the further back you go.

“Clarifying evidence like this mapping of the ejecta layer may allow researchers to test their models and help complete the look into the past.”

The research was published in the Journal of Geophysical Research.

HOW DINOSAURS WENT EXTINCT AROUND 66 MILLION YEARS AGO

Dinosaurs ruled and dominated the Earth about 66 million years ago before suddenly becoming extinct.

This mass extinction is known as the Cretaceous-Tertiary extinction.

For many years it was believed that climate change was destroying the giant reptiles’ food chain.

In the 1980s, paleontologists discovered a layer of iridium.

This is an element that is rare on Earth but found in large quantities in space.

When this was dated, it coincided exactly with the time when dinosaurs disappeared from the fossil record.

A decade later, scientists discovered the massive Chicxulub Crater at the tip of Mexico’s Yucatán Peninsula, dating from the period in question.

The scientific consensus now says that these two factors are linked and both were likely caused by a giant asteroid crashing into Earth.

With the projected size and impact speed, the collision would have created an enormous shock wave and likely triggered seismic activity.

The fallout would have created plumes of ash that likely covered the entire planet, making it impossible for the dinosaurs to survive.

Other animal and plant species had a shorter span of time between generations, which allowed them to survive.

There are several other theories as to what caused the demise of the famous animals.

One early theory was that small mammals ate dinosaur eggs, and another proposes that toxic angiosperms (flowering plants) killed them.

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