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The Effect of Impacts. The Disappearance of the Dinosaurs. Just How Abrupt Was It?. Limited Resolution. First Evidence Suggesting a Catastrophic Event. Discovery of the thin KT Layer [K = Cretaceous] It is relatively high in Iridium contains lots of ash and soot
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First Evidence Suggesting a Catastrophic Event Discovery of the thin KT Layer [K = Cretaceous] It is relatively high in Iridium contains lots of ash and soot is seen world-wide, typically several cm thick is considerably thicker in southern parts of N America
Different fossils are seen below (earlier) and above (later) the KT layer (Not just dinosaurs! All sorts of life forms, including micro-organisms)
More Iridium than you would expect (But still only a few parts per million - it’s quite a rare element!)
Analogy At a murder scene, we find a tiny trace of my DNA (perhaps from a drop of sweat) although I claim never to have been there It’s not the dominant material present, but it is surprising to find it at all (and it may be an important clue!)
The Puzzle Earth has its fair share of Iridium, but most of it is in the core, thanks to differentiation. So where did the extra Ir in the KT layer come from?
Three Obvious Possibilities Perhaps a period of enhanced volcanic activity dredged Iridium up from deeper layers (and the volcanism killed off many species, including the dinosaurs); or Perhaps a big impact (by an asteroid, say) blasted out a lot of material from deep within the Earth, including Ir; or Perhaps an incoming object, with its own share of Iridium, broke up on impact, and sprinkled its own material (and some stuff from the Earth’s crust) all over the planet.
Other Pointers Evidence of extensive fires Impact site found, surrounded by ‘ejecta blanket’ Near the site, “shocked” quartz crystals, evidence of direct impact Evidence of huge tsunamis Impact site has the right age!
Evidencefor Huge Fires- lots of soot and organic material inthe KT layer
The Impact Site-100 km diameter crater suggests impact by 10 km body
After the Impact (artist’s impression! – now eroded and overgrown)
Why the Extinctions? A gripping tale!
First: Would There Be Global Damage? Would the impact of the asteroid have a significant effect on the Earth as a whole? Rupture it? Knock it out of its orbit? A 10 km rock would have about 1 trillionth of the mass of the Earth
Analogy Mosquito mass ~ 1/1000 gm Mass of a Boeing 747 = ~ 400,000 kg That’s also a factor of about one trillion. When they collide, what happens to the 747? Nothing!
But the Biosphere Will be Affected! The asteroid (10 km diameter) has a mass of about 4 trillion tons It is coming in at perhaps 25 km/sec On impact, it releases as much energy as about 100 trillion tons of TNT
Chicxulub Is equivalent to about a billion such huge hydrogen bombs! This is many millions of times greater than all the nuclear weapons on Earth, piled up and detonated at once
Remember, However: The energy released is simply kinetic energy (It’s like a lead bullet hitting your body at very high speed, doing traumatic damage.) There are no explosive materials, no radioactives, no nuclear reactions…
Does the Atmosphere Protect Us? No. (Does your skin protect you from a bullet?)
The Immediate Consequences Fairly locally: There are atmospheric shock waves from the supersonic flight of the asteroid. (Remember Chelyabinsk?) The pressure causes enormous heating of the air. Animals and plants in the vicinity crumple up “…like cellophane in a fire” (B. Bryson) The impact causes tsunamis and a big ‘ejecta blanket,’ and vaporizes a lot of sea water
More Widespread Pulverized material (from the asteroid and the crustal rocks) is thrown into the air – many billions of tons If falls back in pieces like uncountable numbers of meteors, glowing red hot The whole sky lights up like a blast furnace Grasslands and forests over much of the Americas erupt in flame (hence the soot)
But the Real Damage Comes Later! ‘Nuclear Winter’ - the foreseeable consequences of a nuclear war
Soot and Smoke Fill the Air- the Earth enters a long ‘deep freeze’
Can It Happen Again? Yes. We are in a ‘cosmic shooting gallery’ Because asteroids are low-mass, their orbits are constantly being perturbed by the gravity of Jupiter and the other planets So we cannot safely predict their orbits into the remote future, even if we could find all the dangerous objects now
There are Recent Examples- and lots of near misses Tunguska – 1908 Near miss captured in home movie (1950s) Shoemaker-Levy – 1994 Toutatis - 2004 Chelyabinsk - 2013
What Are the Chances? For every big asteroid, there are millions of mid-sized ones and trillions of pebbles. So big impacts are relatively rare.
Don’t be Complacent! A KT event happens, on average, once every 100 million years (My) The most recent was 65 My ago This does not mean that we are safe for the next 35 MY!
How Can We Protect Ourselves? The critical point is early discovery. Hence NEO (‘Near Earth Orbiter’) surveys and programs. Find all the potential problem objects!
