Earth after mass extinction event by asteroid

Question

Let say a asteroid hit earth and you survived in a bomb shelter. How long would you have to stay in that bomb shelter before it was safe to leave it? How would earth look when you got out from the bomb shelter, would it be hotter or cooler? would there be still be tree and other plants? What else would be different?

Answer 1

Sources:

• Documentary Catstrophe (2008)
• Documentary Miracle Planet (2008)
• Radek Michalik and David Dolak impact visualization that was created in collaboration with the Science Institute at Chicago's Columbia College.

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IMPACT A: Catastrophe and Michalik & Dolak explore the Chicxulub impact, to which it is attributed the extinction of the Dinosaurs. The impact is described as follows (added unit convertions):

• 6 miles wide (9.656 km ~10km)
• 45000 mph (72420 km/h or 20.12 km/s) [Michalik & Dolak estimate 22 km/s (49213 mph or 79200 km/h)]
• On Yucatán Peninsula.
• 65 million years ago.
• Chicxulub impact crater is oval, suggesting a non vertical impact.

Note 1: None of the documentaries give an acurrate measue of wheight of the asteroid, although Catastrophe says it was "about a trillion tons".

Note 2: The extinction of the dinosaurs is dated thanks he an iridium layer (stata) that is uniformly tick around the world. Below the iridium layer there are dinosaur fossils, above there aren't. Iridium is otherwise rare in the Earth's crust, but it is found in meteorites... the impact that would have created the iridium layer is known as KT (Cretaceous–Tertiary) event. When discovered the Chicxulub crater was attributed to the KT event, but other research suggest that there may have been two Dinosaur killers, being the Chicxulub the first one, and the KT even the second. Regardless of whatever that is true or not, we talk about the Chicxulub impact (which may or may not be the KT event).

IMPACT B: From Miracle Planet an hypotetical event in modern times with the following description is taken (added unit convertions):

• 500 km (310.7 miles)
• 20 km/s (44739 mph or 72000 km/h)
• On the pacific ocean, 1000 miles (1609 km) south of Japan.
• If the impact would happen today.
• Angle is not stated, but probably it is a vertical impact.

Note 3: I'm getting misleading information from Miracle Planet, in particular it says that the asteroid size 500 km but also that "the asteorid diameters is larger than the main island of Japan" while Honshu is larger than 500 km (with 1300 km according to Wikipedia). Also, it claims that the speed is 20 km/s which coverted to km/h is 72000 km/h but when the documentary mentions the speed in km/h it says it is 720000 km/h (10 times faster). Also - as possible artistic license - the video present the impact to the east of Japan instead of to the south. The information above prefers the more conservative measures and the spoken material of the displayed one.

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First hours

A lot of (the debris) makes it into the upper atmosphere and some of it even makes it out of the atmosphere and it orbits in space of a little bit and then re impacts into the surface of the Earth somewhere else. So this debris actually went all over the surface of the Earth, and as it was coming back in - just like when you see in a meteor shower - things heat up as they come back in to Earth's atmosphere. This debris would have heated up too, but there were so much of it that it would have heated up the entire atmosphere and start forest fires just from spontaneous combustion on the opposite side of the globe.

-- Cathy Plesko

When an asteorid hits the surface Earth, the material is heated up to temperatures that get up to the point of... say, 4000 ºC to 6000 ºC. This is as hot as the surface of the sun.

(...) So, heat really is the killer.

(...) But that is only part of it, you then have the vapor that expands, and heats up the atmosphere as well.

(...) it will expand extreamly fast. It expands so quickly that it can cover - eventually - the entire planet.

So now you are not only beating the point of impact and the vapor that's created there. You now have material that is expanding, eventually some of that material is expanding and goes out of atmosphere of the Earth, then comes back down.

During the time when it comes back down... it's generating more radiation. So that you have the heat of the impact, then you have the material - that vapor - that heats the atmosphere. Then you have the jets that return to the surface of the Earth... and as it goes to the atmosphere it will create enough energy to literally fry - completely combust - any living organism that would exist.

-- Peter H. Schultz

As per Michalik & Dolak model, global darkness is reached in the initial 3 weeks after the impact.

No sunlight

After the fast effects, it is expected to have an initial period of heat followed by drakness from dust covering the atmosphere. This period may last at least 6 months - 3 years as per Michalik & Dolak model.

In IMPACT A, the darkness period is cold as the heat disipates relatively fast. For IMPACT B, the darkness period is extremely hot, and it is said to boil the oceans.

For IMPACT B it is said that the heat travels slowly into the Earth crust - "about 1 meter or 3 feet every year".

Any organisms that are living deep underground like (under) one to two kilometers tick (rock), will probably safe. The heat part doesn't last long enough for the heat to propagate down to that depth.

-- Normal H. Sleep

Cold period

After the darkness period, sunlight comes but the temperature stays low in a permanent winter.

In IMPACT A, the cold period means permanent snow. There is also acid rain, the cold and acid rain prevent growth of new plants. This period may last "a couple" years.

So, at first you have the dust launched out of the atmosphere which blocks out the sun. That eventually falls back as the atmosphere converts and cleans itself out. But then you still got the sulfur acids up at the upper atmosphere, which reflect sunlight and cool the planet. So this prolongs the impact winter for probably another couple of years.

(...)

First you have this six month long winter when there is no sunlight at all, and then finally you get a little bit of sunlight and the plants think "oh good, finally I can sprout my seeds and grow again" and then the sulfur dioxide falls in acid rain and burns all the leaf off your plants.

-- Cathy Plesko

In IMPACT B, since water is mostly vapor at the end of the darkness... the winter bring torrential rains.

Restoration

After the cold period, is probably the best moment to try to get out, as the restoration process will take centuries. In both scenarios there wouldn't be plants let alone animal life to be found.

Following the cold period, comes an warming that may last "several centuries". But the magnitud and conditions are different for each of the studied impacts.

It is not clear at waht point plants would be able to grow safetly again.

IMPACT A

It is said that it increased 20 ºC in 100 years. The planet is mainly desertic at this time. Snow retreats rapidly during the initial years.

The carbon dioxide was the last effect of the impact, and it hang on for centuries. Now warming the planet instead of cooling it. So, the climate is then artificially warmed and not returning to normal values for several centuries after the impact.

-- Cathy Plesko

IMPACT B

The planet also becomes warmer, but not at the scale that it happens in IMPACT A. Since water wasn't in permanent snow - but in vapor instead - the following centuries are of heavy rain as all the water return to form the oceans again.

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Affiliation:

• Cathy Plesko is a Research Scientist in Applied Physics at Los Alamos National Laboratory.
• Peter H. Schultz is a Professor at the Department of Geological Sciences at Brown University.
• Norman H. Sleep is a Professor of Geophysics and Geology at the Stanford University.