Asteroid Strikes 'Increase Threefold Over Last 300 Million Years,' Survey Finds (theguardian.com) 80
According to a survey of asteroid craters at least 6.2 miles wide, the number of asteroids slamming into Earth has nearly tripled since the dinosaurs first roamed. "Researchers worked out the rate of asteroid strikes on the moon and the Earth and found that in the past 290 million years the number of collisions had increased dramatically," reports The Guardian. "Before that time, the planet suffered an asteroid strike about once every 3 million years, but since then the rate has risen to once nearly every 1 million years." From the report: The findings suggest that the dinosaurs may have been unfortunate in evolving 240 million years ago, just as the odds of being wiped out by a stray asteroid were ramping up. It was one of those impacts, on top of other factors, that did for the beasts 66 million years ago. Many scientists had assumed that asteroid strikes were a rare but constant threat in Earth's deep history, but the latest study challenges that belief.
Writing in the journal Science, the researchers describe how they turned to the moon to examine the violent history of Earth. The Earth and moon are hit by asteroids with similar frequency, but impact craters on Earth are often erased or obscured by erosion and the shifting continents which churn up the crust. On the geologically inactive moon, impact craters are preserved almost indefinitely, making them easier to examine. Using images from Nasa's Lunar Reconnaissance Orbiter, the scientists studied the "rockiness" of the debris surrounding craters on the moon. Rocks thrown up by asteroid impacts are steadily ground down by the constant rain of micrometeorites that pours down on the moon. This means the state of the rocks around a crater can be used to date it. The dates revealed that the moon, and by extension the Earth, has suffered more intense asteroid bombardment in the past 290 million years than at any time in the previous billion. On Earth there are hardly any impact craters older than 650 million years, most likely because they were eroded when the planet became encased in ice in an event known as Snowball Earth.
Writing in the journal Science, the researchers describe how they turned to the moon to examine the violent history of Earth. The Earth and moon are hit by asteroids with similar frequency, but impact craters on Earth are often erased or obscured by erosion and the shifting continents which churn up the crust. On the geologically inactive moon, impact craters are preserved almost indefinitely, making them easier to examine. Using images from Nasa's Lunar Reconnaissance Orbiter, the scientists studied the "rockiness" of the debris surrounding craters on the moon. Rocks thrown up by asteroid impacts are steadily ground down by the constant rain of micrometeorites that pours down on the moon. This means the state of the rocks around a crater can be used to date it. The dates revealed that the moon, and by extension the Earth, has suffered more intense asteroid bombardment in the past 290 million years than at any time in the previous billion. On Earth there are hardly any impact craters older than 650 million years, most likely because they were eroded when the planet became encased in ice in an event known as Snowball Earth.
oort cloud (Score:4, Interesting)
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Just to be clear, this is three times (three times as likely). Threefold is much greater. It is double, three times.
Threefold?? (Score:2)
I don't believe it. In my more than half century of life I've never heard of the -fold suffix being used in the way you describe, and quick search only turns up references (including a Wikipedia page) that equate it with "times". If you have any source for your assertion, I'd like to see that.
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The phrase originally was used to mean a reduction; take a piece of fabric and fold it in half, then fold it in half again, then fold it in half a 3rd time, and what you have is a "three fold reduction" which would be 1/8th of the original.
How much "originally"? The OED cites "threefold" in the sense of "three times as X" all the way back to 1200. "Fourfold" in a similar sense it cites from year 1000. Furthermore, it doesn't cite your purported meaning at all!
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Their working theory is a collision in the asteroid belt 300 million years ago which suddenly caused a large increase in the number of rocks available to impact. If true though then presumably the same sudden increase in rate should be visible on other planets too.
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That does not explain the rate suddenly increasing 300 million years ago.
Are you saying no stars passed by 300 million years ago?
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Which stars? They could literally be on the other side of the galaxy by now.
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as rocks are pushed into the inner solar system removing them from the belt.
And why would that be the case?
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In this context, there is a lot of work supporting a brief (around 20 million years) period of increased micrometeorite delivery to Earth, which are recorded in "shelf carbonates" of the Ordovician series. Actually the record is getting good enough that people are arguing for several distinct pulses of micrometeorite delivery within that period. Of the less-altered micrometeorites analysed, they appear to be significantly less div
Re: oort cloud (Score:1)
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On a much longer timescale, this work is suggesting that there has been a persistent increase in cratering events in the Eart
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That's a bit of a stretch, but trump is one of the major threats to human extinction.
So what you are calling for is human extinction? Cant have any threats to it?
You sound like those Christians yearning for Armageddon.
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You sound like those Christians yearning for Armageddon.
They haven't learned their lesson from 1998? What good will a remake do?
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Sociopaths, we call them, and there seem to be a lot of them about recently. Of course, they are also idiots if they think a single politician can somehow destroy the most adaptive species every to arise. That also has a name, Trump Derangement Syndrome.
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Constant? (Score:5, Interesting)
How do we *know* the rate of micrometeorite bombardment is constant and hasn't dropped in intensity by a third in recent (geological/selenological) times?
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It's possible two (formerly) big asteroids collided fairly recently, creating a lot of debris.
We need higher taxes (Score:1)
Governments must have the means to combat asteroid growth.
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Or maybe... (Score:3)
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In short, no. If we can find evidence of craters older than 300M years, then we can't take them into account. Pangaea was 335M years ago. It's no coincidence that the big craters we know of postdate that time. Evidence of older ones has been subducted. How do you think we would account for them?
Re:Or maybe... (Score:5, Informative)
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That tells us the relative ages of the craters on the moon, but not their ages...
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Or maybe you should read the article.
I read the article. It doesn't explain what I actually needed to know. See, there has been a lot of speculation as to how reliable our estimates of the ages of craters on the moon have actually been. What TFA doesn't mention is that these findings are the result of "using a new method to date craters on the moon [theconversation.com]". The Guardian simply didn't bother to explain how they actually figured this out. As usual on Slashdot, we get the worst possible link attached to the story.
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How do you think we would account for them?
Well, we could dive for them, or not?
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Errr, doh? So, in your immense knowledge you've never heard of the Sudbury structure - a Grenville age large astrobleme near the Canada-USA border, from about 950 Myr ago. Or the Stac Fada structure recently discovered in Scotland, dating from approximately 1.1 Gyr? Or the Vrefefort structure, one of the largest on the planet and about 2 Gyr ?
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6.2 miles? (Score:2)
Who do you think is the reading audience here, that they would be so badly thrown off by using km? I think /. readers are smarter than that.
--
.nosig
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And it's not like it's hard to do both.
How long have Saturn's rings been there? (Score:2)
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Has anyone tied this, snowball earth and the great nonconformity together? the eons roughly match.
Yes there was a news story about this three weeks ago [nationalgeographic.com].
Asteroid Strikes (Score:2)
I didn't even know there was a union.
Because of climate change obviously. (Score:2)
What else could it be?