66 Million Years Ago
Now, in the grand scheme of things, 11 to 81 kilometers isn’t that big, especially compared to the planet itself. The mass of the asteroid was less than that of a single mountain range, but it's important to understand how it compares to the fluids on the surface.
The atmosphere stretches about 100 kilometers high, but at that altitude it’s so thin it’s practically a vacuum; most of it is densely packed into the first 10 kilometers. The lower limit to the size of the Chicxulub asteroid is still taller than the majority our atmosphere; as it hit the Earth, it’s far side was still in space!
Here’s a map of the impact site, the Yucatan peninsula on the Gulf of Mexico:
The underwater portions on this map are still part of the continental shelf, so the maximum depth of the water would be about 100 meters. To scale with our atmosphere it looks like this:
You can’t even see the dark blue strip on the bottom! The asteroid wouldn’t even notice the water. It would hardly notice the atmosphere! Whenever it’s depicted in a textbook or on TV, it looks like this:
as if it’s streaking through our atmosphere and burning up on entry. That could not be less accurate. It would be moving so fast you wouldn’t even be able to see it. It’s an asteroid orbiting the sun at the same distance as Earth, and if we assume it has the same orbital velocity as Earth, it would be moving at 107,000 kilometers per hour; that’s almost 30 kilometers per second. One second it’s in outer space, the very next second it has impacted the Earth; it wouldn't be slowed down by the atmosphere at all, it’d be over before you even realized it was coming. At that speed, a spacecraft could go from Earth to the Moon in 3.5 hours.
The asteroid would displace both the water and the atmosphere as it impacted, pushing it, compacting it into a wall of gas; wind speeds would be astronomical as 11 kilometers of oxygen and nitrogen are pushed out of the way in a fraction of a second. All of the water would be pushed out of the way in an instant by Mega-Super-Ultra-Hurricane-force winds, so the asteroid would impact the dry seafloor (though again, this all happens so fast it would be impossible to observe)
It would strip away the atmosphere; hell, it would start stripping away the Earth itself! The impact would release more energy than every nuclear bomb ever detonated combined, literally punching a hole in the Earth’s crust. The resulting crater is 20 kilometers deep and 150 kilometers wide.
Seismic waves propagate through rock at about 6 kilometers per second, so if the energy traveled straight through the Earth’s core it would take almost 40 minutes for the earthquake to be felt on the opposite side of the world (a point in the Indian Ocean between Australia and Madagascar). If you were in Indonesia when it impacted, you’d probably see it before you felt it. The asteroid would have ejected so much molten material into space at such high velocities that the fallout would orbit the Earth and rain down all over the planet in a matter of minutes. The horizon would light up all around you as the sky literally caught fire in every direction you looked.
From the impact site, the wall of fire and molten crust thrown outward at the surface would reach over 1000 kilometers away. In a matter of seconds, the firestorm would kill everything from Miami to New Orleans to Mexico City, pretty much the entirety of the Caribbean and Central America. All over the world, you’d feel the most powerful earthquake ever recorded, and while most of the water within several hundred kilometers would have been vaporized, the resulting tsunami would destroy the entire Atlantic coasts of the Americas and Africa. The waters would flood inland up the Mississippi River valley maybe as far as modern Memphis. As it propagated, West Africa would be devastated, the Iberian peninsula would be devastated, Northern Europe and the Arctic would be devastated,
It would be the apocalypse.
