Asteroid Storm 800 Million Years Ago May Have Caused Snowball Earth

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Asteroid Storm 800 Million Years Ago May Have Caused Snowball Earth

If an asteroid shower hit the Moon, it hit the Earth too, say Japanese scientists. That could even be the elusive catastrophic event leading to planetwide glaciation

 

Artist's impression of an asteroid shower hitting the moonCredit: Murayama/Osaka Univ.

 

The geomagnetic field at Earth’s surface with the South Atlantic Anomaly outlined in black and St. Helena marked with a star. Colors range from weak fields (blue) to strong fields (yellow). Image via

 

Richard K. Bono/ The Conversation.

 

This “reverse flux patch” itself has grown over the last 250 years. But we don’t know whether it is simply a one-off product of the chaotic motions of the outer core fluid or rather the latest in a

 

series of anomalies within this particular region over long time frames.

 

If it is a non-recurring feature, then its current location is not significant – it could happen anywhere, perhaps randomly. But if this is the case, the question of whether its increasing size and depth

 

could mark the start of a new reversal remains.

 

If it is the latest in a string of features reoccurring over millions of years, however, then this would make a reversal less likely. But it would require a specific explanation for what was causing the

 

magnetic field to act strangely in this particular place.

 

Volcanic rocks

 

To find out, we travelled to Saint Helena – an island in the middle of the South Atlantic Ocean. This island, where Napoleon was exiled to and eventually died in 1821, is made of volcanic rocks.

 

These originate from two separate volcanoes and were erupted from between eight million and 11.5 million years ago.

 

Studying geological phenomena on Earth has to start with spotting them. Over the eons, tectonic movements and erosion reshape the landscape. Even if it survives, an impact crater can be so big

 

that it escapes notice. Chicxulub, for instance, is about 150 kilometers in diameter, and half of it lies under the sea. It took decades from the discovery of anomalies by geophysicists looking for oil

 

in the late 1970s for the crater’s existence to be accepted.

 

Scars on the Moon are hardier, even though the Moon also experiences “weathering,” erosion and seismic spasms, it turns out.  Seismometers placed by American astronauts on the lunar surface

 

revealed moonquakes up to 5 on the Richter scale in the mantle and crust. They may be, it has been postulated, echoes from a particularly violent impact in the Moon’s early years, 4.3 billion years

 

ago. And at least some moonquakes may stem from the Moon continuing to cool and contract.

 

But all in all, the lunar surface retains impact scars for eons, and now the Japanese team reports studying the formation ages of 59 large lunar craters with a diameter greater than 20 kilometers.

 

The study is based on images captured by the lunar orbiter spacecraft Kaguya (“Moon Princess”), launched by the Japan Aerospace Exploration Agency in 2007. The team also factored in data from

 

the glass spherules that formed when meteorites slammed into silicate soil and were brought earthward by some of the Apollo missions.

 

(Click here for images from Kaguya and here for its last images before crashing into the Moon as planned in 2009.)

 

Eight of the 59 lunar craters were created at about the same time, the team deduced. They postulate that a sporadic bombardment by meteoroids occurred across the whole Moon and dated the

 

sequence of impacts to about 800 million years ago.

 

Truth be told, there is some discrepancy in the chronology. But the main point, the scientists explain, is this: “The most important of the new findings is that eight craters, including Copernicus,

 

show identical relative ages based on a constant flux model.”

 

It seems the Earth, for one, has experienced this sort of thing before: almost half a billion years ago, apparently, an asteroid suffered an impact in outer space and broke up. Its debris caused a

 

shower of meteors on Earth that lasted millions of years, and may have resulted in the Ordovician “icehouse conditions” and extinction event, which was followed by the great Ordovician

 

biodiversity event.

 

And maybe it wasn’t the first time that happened. About 800 million years ago, the team estimates, a total asteroid mass of 40 to 50 million billion kilograms collided with the Earth, which likely

 

would have had a dramatic result.

 

Colder, colder, freezing point

 

To estimate the date of the large impacts on the Moon, the team calculated the density of later impact marks between 100 meters to 1 kilometer “atop” the 59 large craters (i.e., in the ejecta).

 

One of the 59 is the famous Copernicus crater, around which the team detected and examined no less than 860 later craters, each 100 to 1,000 meters in diameter.

 

They concluded that eight of the 59 craters had formed at the same time, which means the Moon had been hit by an asteroid shower. If it had, the Earth had too.

 

The timing of this meteoroid shower was shortly before the onset of the Cryogenian era, which began about 720 million years ago.

 

The Cryogenian was apparently the most extreme ice age the planet has known, though scientists continue to argue over whether the early life-forms on the benighted planet were living on

 

Snowball Earth – completely frozen over – or Slushball Earth, which retained some open ocean.

 

Either way, despite the inhospitable conditions, some unicellular life in the seas at least survived and the first known sponges, which are animals, appeared. Despite suspicions that the icebound

 

oceans were woefully short of oxygen, fossils of early sponges appear between fossil bacterial mats from the period.

 

Until now, the thinking has been that the Cryogenian was caused by intense volcanism as the supercontinent Rodinia broke up. Now, based on the exquisite study by the Japanese team, a

 

different theory may come to mind.

 

Could the meteoroid shower peppering Earth around 800 million years ago have kicked up enough dust or caused volcanism – or in some other form, caused the equivalent of an extremely

 

protracted volcanic winter?

 

Maybe, maybe not, Terada answers. But it could be. “It is considered that Chicxulub impact formed the dusty atmosphere over years, causing the darkness and cooling 66 million years ago,” he

 

tells Haaretz.

 

Also, he adds: “A meteoroid shower occurred on the Earth 470 million years ago. Recently, Schmitz et al. (2019) suggested that after the meteoroid shower, the extraordinary amounts of dust

 

during 2 million years cooled the Earth and triggered the Ordovician icehouse conditions, sea-level fall, and major faunal turnovers related to the Great Ordovician Biodiversification Event.”

 

The mass the team calculated for the asteroids that hit Earth 800 million years ago is 10 to 100 times greater than the Chicxulub impact, and also compared with the meteoroid shower 470 million

 

years ago. So, Terada sums up, it is plausible that this celestial shower they now report might have triggered the Snowball or Slushball. You can decide for yourself which theory you prefer.

 

All we can say at this point, as Terada implies: The chronology of the asteroid showers detected on the moon, and therefore inferred for Earth, looks awfully like a smoking gun behind the

 

planetwide glaciation – a condition that persisted for some 100 million years. Ironically, for the geologically emotional among us, the very advent of worldwide glaciers crushing the land below

 

would have erased the scars of the asteroids that caused them.

 

Orbital photo of lunar surface, showing evidence of volcanic activity, dense cratering, mountain ridgesCredit: NASA

 

Crater Copernicus on the Moon. Mosaic of photos by Lunar Reconnaissance Orbiter, made with Wide Angle Camera. Size of the image is 150×150 km, north is upCredit: JMARS / NASA

 

Mountain ridges rising above the regolith on the moonCredit: Project Apollo Archive

 

 

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