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Oct 7th 2020

The Chicxulub Crater: Of Asteroids and Armageddon

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Sixty-five million years ago wasn’t a great time to be a dinosaur.

After nearly 165 million years of evolution and expansion across Earth’s surface, the Chicxulub impactor swung into our solar system. This 6-mile-wide asteroid slammed into what’s now the northern coast of Mexico’s Yucatan Peninsula, causing the Chicxulub crater and creating an inhospitable environment for the planet’s previous inhabitants.

But is that the whole story? While some scientists see Chicxulub as the “smoking gun” of dino destruction, others are less convinced about the notion of asteroid Armageddon.

What’s in a Name?

The crater and impactor get their monikers from the town of Chicxulub, the closest human settlement to the site. The dinosaur-destroying object itself, however, is sometimes called a comet, meteor or asteroid. But what’s the difference?

Simply put, it’s a matter of size. While there’s no standardized measurement, meteors, meteorites and micrometeoroids are typically small, ranging from the size of pebbles down to grains of sand. Asteroids and comets, meanwhile, aren’t fooling around: Massive asteroids such as Ceres — measuring a substantial 592 miles in diameter — are considered dwarf planets. While the Chicxulub impactor wasn’t quite so big, its 6-mile size was enough to change the course of life on Earth.

Later, Crater

Evidence of the impact crater was first found in 1978 by Antonio Camargo and Glen Penfield, but they weren’t able to directly connect their observations to an asteroid impact. In 1980, Nobel Prize-winning physicist Luis Alvarez and his son, Walter Alvarez, suggested that increased deposits of iridium in 66-million-year-old clay — an element extremely rare on Earth but often found in space — lent credence to the Chicxulub crater theory. In 1990, evidence including melt spherules and shocked quartz were found at the impact site, indicating the presence of massive heat and pressure caused by an asteroid impact.

Later investigations also revealed a ring of buried, circular hills that contain granite rocks “out of order” with other sedimentary strata. This “peak ring” is common on other planets after impacts but hadn’t been directly observed on Earth — it occurs when rock such as granite is superheated and begins flowing like liquid. In the case of Chicxulub, rock likely rebounded into a 10-meter tall tower before collapsing under its own weight and spreading out to form a ring of “hills” around the central impact site.

Today’s Forecast? Terrible

While the initial outcomes of asteroid impact were awful — including massive waves, huge tsunamis, coastal wildfires and a massive heat pulse that could be felt more than 900 miles away — things only got worse from there. Part of the problem came from the fact that this was a worst-case scenario: Not only did the asteroid hit with a steeply-inclined trajectory — 45 to 60 degrees to horizontal, according to Nature — it also crash-landed near a coastline. If the Chicxulub impactor had come in a little less hot or hit farther out to sea, the outcome might have been problematic rather than pandemoneum.

This leads to the biggest problem with our prehistoric impactor: climate change. Not the current kind that comes with political and scientific push-pull, but the kind that likely caused a drop in temperature almost immediately thanks to volcanic aerosols. While temperature levels returned to near-normal in a matter of years, it took decades to overcome initial impact deficits. Not surprisingly, this wasn’t ideal for dinosaurs — almost overnight, their habitats worldwide were destroyed.

Let’s Talk Traps

There’s no denying the massive impact — both figuratively and literally — of the Chicxulub impactor. But while its massive size seems like the kind of thing that ends arguments, the confirmation of out-of-this-world cratering started an entirely new set of speculations around exactly what killed the dinosaurs.

It all comes down to the Cretaceous-Tertiary (K-T) boundary, which marks the transition from one historical period to the next and ushers in the framework for more familiar terrestrial life. Though an explosion with the force of 100 million tons of TNT can’t possibly be good for life on Earth, there’s evidence to suggest that the Chicxulub impact predates the K-T boundary by up to 300,000 years and can’t be the direct cause of dinosaur demise.

Volcanoes are another option — wild volcanism is historically associated with significant extinction events, and as noted by Ars Technica, the end of the Cretaceous period saw massive eruptions along the Deccan Traps, in turn burying most of what’s now India under lava and causing significant climatic change. While variable volcanism actually drives temperature increases that could offset some of the asteroid-induced atmospheric occlusion, volcanic ash poses its own problems for dinosaurs just trying to survive. While both asteroid and exploding mountains likely contributed to the end of dinosaur existence, that doesn’t stop experts and amateurs from championing their personal best-fit theory for Cretaceous calamity.

Significant Impact

Meteors and asteroids play an undeniable role in Earth’s history, ranging from the mildly curious — such as King Tut’s meteorite dagger — to the massively catastrophic, such as the Chicxulub impactor. And while debate remains over the exact level of disparate dinosaur destruction caused by this outer space interloper, there’s no denying that dinosaurs can lay claim to one of the worst days in Earth’s history.

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