Science Camp: The Alvarez Hypothesis

Week Two: A Distrust of Received Wisdom

As a kid I had, as New Scientist would call it, a “distrust of received wisdom.” In early school I sat at the back of classrooms quietly sceptical, watching teacher after teacher strut in front of the blackboard. Sure my teachers were much older than me. They ate their dinner with proper cutlery and stood at the head of the classroom with the chalk. But I praised myself for my common sense. So at the age of seven, sitting in the school library with a book about dinosaurs, I had a real bone to pick with my Year 2 teacher.

The Alvarez Hypothesis suggests that an asteroid hit the Earth about 66 million years ago, marking the end of the Cretaceous period and bringing about the demise of every single curiously colourful dinosaur in the book I was holding.

It all sounded rather dramatic to me. If I hadn’t been so shy, if I’d been even a year and a half older, I would’ve asked: Shouldn’t there be more to it?

Yes seven-year-old me. Yes there was.

(INSERT CATCHY THEME SONG)!!!

The Beginning

Back in the day Little Me didn’t understand how an asteroid could kill an entire species without destroying the planet, but that was because Little Me wasn’t quite getting the whole picture.

Luis and Walter Alvarez

In 1977 father and son Luis and Walter Alvarez were studying limestone rocks outside the small Italian town of Gubbio. They were looking for geological records from the Cretaceous period — searching the strata for different substances — when they found something in the clay they weren’t expecting (DUN DUN DUN)! They found rare Earth metal, iridium.

Thing is, iridium is much more likely to be found on the back of an asteroid than on an expedition in Italy. And there was lots of it — we’re talking 20, 30, 160 times the amount found in background samples. There were also two other rock-solid pieces of evidence for what would come to be the Alvarez Hypothesis.

Really, actually rock-solid.

From what we know about the impact craters of asteroids and meteorites, they usually contain shocked quartz and tektites, both of which were present at the Cretaceous-Tertiary boundary (or K-T for short — they both mean The Death of the Dinosaurs).

Shocked quartz is a form of quartz, only its structure is deformed because of intense pressure. AKA, it’s quarts except it looks like it’s been hit by an asteroid.

Shocked Quartz, looking all psychedelic. A. Hildebrand

Tektites are small, black objects made up of Earth material — after that Earth material has been hit by a meteor, thrown into the atmosphere, and rained back down again.

Luis and Walter Alvarez, and two other (unrelated) scientists, Frank Asaro and Helen V. Michel, published their findings in the journal Science under the somewhat inflammatory title: Extraterrestrial Cause for the Cretaceous-Tertiary Extinction.

The War of the Theories

And thus the world was split into two sides — figuratively (I know we’re all a bit touchy about world destruction given the current topic).

On one side of the ring we had intrinsic gradualists, who thought the K-T extinction came about gradually because of naturally occurring events on the Earth. They pointed volcanic activity bursting from the Earth at the time, spilling forth mantle conveniently rich in that telling metal iridium. The activity would have caused significant climate change, which is never a great thing for a species that wishes to survive. Also, the oceans were receding because of plate tectonics. It was all very apocalyptic.

On the other side of the ring we had extrinsic catastrophists, with a much cooler sounding name. They thought the extinction came about suddenly because of extraterrestrial events, with the asteroid as the cataclysmic culprit. The biggest weakness of the extrinsic catastrophists — that a crater suitable to the hypothesised 10km wide asteroid had yet to be found — was resolved in 1991, when a crater suitable to the hypothesised 10km wide asteroid was found.

The Chicxulub crater is over 180km in diameter, and it was a real kick in the butt to the intrinsic gradualists.

Illustration by Detlev van Ravenswaay, Science Source

The Death of the Dinosaurs (And a Whole Bunch of Other Stuff)

I still need to answer my past self — Shouldn’t there be more to it than an asteroid? Well, in 2016 the world is far less divided about what killed the dinosaurs. In fact a lot of people, when learning about the dinosaurs, were taught the Alvarez Hypothesis as fact. An asteroid killed the dinosaurs. It’s still a hypothesis, but it’s a popular one.

Many suspect that both the intrinsic gradualists AND the extrinsic catastrophists were right. Dinosaurs, as well as the marine and plant life of the time, were probably struggling well before their Armageddon.

What we DO know is that the climate changed dramatically over a short period of time, cooling about 7 degrees in some places. The Earth was struck with a bout of overactive volcanoes throughout the tumultuous K-T extinction — kind of like a pubescent teenagers face. And the oceans did recede, killing off fish and plankton frighteningly fast. When the asteroid touched down, it was just the king-hit — either a divine act of dinosaur hate or a really crappy coincidence.

The Aftermath

So no, Little Me. The asteroid didn’t IMMEDIATELY kill all of the dinosaurs. Each species had a much slower, less fiery crawl to the finish line. Some died out before the asteroid hit. Some died during. Many died after, when the debris from the asteroid produced aerosol clouds capable of blocking out 50 per cent of the sun, cooling the Earth, and offering the occasional shower of acid rain for good measure.

If this is dramatic to you, or upsetting, just know that without all of the catastrophe at the K-T boundary, us mammals wouldn’t have had the room to grow and evolve. And if we hadn’t grown and evolved into the always splendid and complicated human race, we wouldn’t have been capable of making films like Jurassic Park.

A posthumous portrait. Cretaceous Sunset Kerem Beyet

Further Reading

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