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That asteroid the headlines have been warning people about isn't likely to actually hit us, and scientists might have solved a mystery that could save lives: the relationship between tides and earthquakes.

Hosted by: Hank Green

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Sources:

http://neo.ssa.esa.int/risk-page
https://www.nasa.gov/feature/nasa-fema-international-partners-plan-asteroid-impact-exercise
https://www.universetoday.com/100025/airburst-explained-nasa-addresses-the-russian-meteor-explosion/
https://www.theguardian.com/world/2013/feb/15/hundreds-injured-meteorite-russian-city-chelyabinsk
https://apod.nasa.gov/apod/ap071114.html
https://science.nasa.gov/science-news/science-at-nasa/2008/30jun_tunguska
https://impact.ese.ic.ac.uk/ImpactEarth/cgi-bin/crater.cgi?dist=1&diam=40&pdens=8000&pdens_select=0&vel=17&theta=45&tdens=2500&tdens_select=0
https://impact.ese.ic.ac.uk/ImpactEarth/ImpactEffects/effects.pdf
https://www.sciencedaily.com/releases/2008/12/081217192745.htm
https://www.nature.com/articles/s41467-019-10605-2
https://www.pmel.noaa.gov/eoi/axial_site.html
https://www.eurekalert.org/pub_releases/2019-06/eiac-sht060519.php

Images:

https://www.youtube.com/watch?v=e5NObStdWFc
https://en.wikipedia.org/wiki/File:Russia-CIA_WFB_Map--Tunguska.png
https://commons.wikimedia.org/wiki/File:Tunguska.png
https://www.istockphoto.com/vector/tectonic-plates-gm812085686-131414477
https://en.wikipedia.org/wiki/File:Earth_cutaway_schematic-en.svg
https://en.wikipedia.org/wiki/File:Fault_types.svg
https://commons.wikimedia.org/wiki/File:Axial_Exaggerated_Bathymetry.jpg
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Click the link in the description to learn more about Skillshare. [♪ INTRO]. I don’t want to alarm you, but chances are that some headline already has, because an asteroid the size of a football field could hit Earth this year.

But the truth is, there is an extremely low chance of that actually happening, and even if it does, it probably won’t cause much damage. The asteroid in question is called 2006QV89. It’s estimated to be about 40 meters in diameter, which is a little less than the width of an American football field.

Not the length, the width, just to be clear. Which, like, who knows the width of a football field? The reason it’s causing such a stir is because the European Space Agency, or ESA, has placed this asteroid on its risk list, which means it has a non-zero chance of hitting Earth.

But that chance is 1 in 7,299. The rule of thumb is that an object needs a 1 in 100 chance of impact to warrant action, so this one isn’t really a concern. And, for context, this asteroid is just 1 of 869 on the risk list, whose impact risks range from 1 in 16 to 1 in 1.84 million.

And you can relax about that 1 in 16 one; it’s only 9 meters across, and it’s not projected to even maybe hit us until 2095 or later. So, it’s nice to know about it. Anyhow, the point is, 2006QV89 is really unlikely to hit us, but the ESA is saying that there’s a chance, albeit a very small one.

Let’s say, for a moment though, that that 1 in 7,299 event occurs and it does hit. To understand what that would mean, we can compare it to objects of similar size that have encountered Earth. Events like that are rare, but they have happened.

For example, the meteor that appeared over the Russian city of Chelyabinsk in 2013 was about 15 meters across. It entered the atmosphere at a shallow angle and ended up breaking apart and exploding in an airburst before touching down. That airburst created a shock wave that broke windows and caused lots of other damage, and over 1,000 people were injured.

Contrast that with the Tunguska Event in 1908 when an object estimated to be between 60 and 100 meters across entered the Earth’s atmosphere and exploded above Siberia. The explosion’s power was enough to level 2,000 square kilometers of forest, but the meteor left no impact crater. And thankfully, it was a sparsely populated area, so there’s no evidence anyone was killed.

If this 40-meter rock does hit, it’s likely to have a similar fate: it will probably break up in Earth’s atmosphere, creating a powerful airburst that has the potential to cause serious damage. But how damaging this would be depends on where it hits. Over 70% of the Earth’s surface is water.

If it hits there, models suggest that waves created could be kilometers high, but they probably wouldn’t make it onshore in any meaningful way, unless the impact was already near a big coastal city. And 95% of the world’s population inhabits just 10% of the land, so it’s just very unlikely for a meteor to impact a densely populated area. If it did, though, and again, the odds of that are super, very, very low, it’s probably worth noting that our latest asteroid impact drill showed we might not totally be prepared to handle it.

In any case, 2006QV89 is still over 6 million kilometers away and isn’t expected to get into striking distance until September. So, enjoy your summer! And speaking of natural disasters, in other news this week, scientists think they’ve solved an enduring mystery about earthquakes.

You see, scientists have known for more than a century that tides can trigger earthquakes far from land, some of which can lead to devastating tsunamis. But the way this happened didn’t make much sense. Earthquake faults are places where two blocks of the Earth’s crust, known as tectonic plates, meet.

When the plates spread, slide against each other, or overlap and slip, you can get an earthquake. Of course, tides don’t affect all of these faults. They seem to have a big effect at mid-ocean ridges, though.

Places where magma rising from the Earth’s mantle forms an underwater mountain range between two plates. The puzzling thing is that if ocean tides trigger earthquakes there, you would expect them to happen at high tide, because that’s when there’s all this water sitting on top of the fault, pushing down the top plate and making a slip more likely. But that’s not what happens.

Scientists have found earthquakes are more likely to happen at low tide. And that did not make any sense. To solve this conundrum, scientists from Columbia University looked at Axial Seamount, an underwater volcano a little under five hundred kilometers off the coast of Oregon.

It sits on a mid-ocean ridge at a hotspot where molten rock rises from the Earth’s mantle to feed the volcano’s magma habit. Axial is the most active submarine volcano in its vicinity. It’s erupted 3 times in the last 25 years.

And because it’s such an eager beaver, scientists have set up with all sorts of instruments to help monitor its activity. The team used data from those instruments to examine what happened during the earthquakes leading up to its most recent eruption in 2015. They found that it’s not the downward forces from the ocean at play.

It’s the upward forces from the magma pocket that feeds the volcano deep beneath the Earth’s surface. At low tide, there’s less water weighing down on the Earth’s crust; the scientists were right about that part. But what they’d missed is that less weight gives the soft, pressurized magma pocket more freedom to expand.

As it does, it pushes the lower plate in the fault upward with respect to the upper plate, then, boom. You get an earthquake. Axial experiences very large tides and it’s extremely sensitive to pressures in the surrounding rock, so it was a particularly good laboratory for these scientists.

Their discovery also explained the activity of another volcano along the same fault. But a few other volcanoes they looked at had too many other things going on to make this the sole explanation. Still, this discovery answers a lot of questions about how tides affect earthquakes, and may even explain why other pressures, like fracking wastewater pumped into the ground, can cause tremors.

And the more we understand about how earthquakes happen, the closer we can get to predicting the ones that impact us. Now, I know what you’re thinking. Deep ocean earthquakes and asteroids barrelling towards Earth sound like SciFi plot devices, and they could be.

But awesome science fiction can’t rest on natural disasters alone; you gotta write a compelling story. And that’s something that you can learn to do better with a few courses from Skillshare. You see, Skillshare offers over 25,000 classes covering everything from cooking to business management.

And they have lots of classes that can help you hone your writing skills, all of which you can access with Premium Membership. You might enjoy author Sabaa Tahir’s class on How to Build a Believable Character, for example. In it, you’ll learn how to build fascinating characters that really drive stories forward, with or without an asteroid strike.

And it’s a Skillshare Original, which means you’ll only find her sage advice on Skillshare! More than 7 million creators are already learning with Skillshare. And joining them is so affordable; an annual subscription will cost you less than $10 a month.

Plus, because you watch SciShow, you could get two months for free! Check out the link in the description for more info on how. [♪ OUTRO].