The Sky is Falling

I saw a show called Mega Disasters on the history channel that was really interesting. The episode explored the catastrophic effects of an asteroid 2 km long hitting just off the coast of Los Angeles. It is widely believed that the Chicxulub asteroid impact of 160 million years ago wiped out the dinosaurs and 70% of all living things. The show used that impact as an example to project what would happen in the theoretical Los Angeles asteroid scenario. As an introduction, the narrator gave a bunch of details about the asteroid that wiped out the dinosaurs. I didn’t realize that we knew so much about it, but the following are some of the details.

The asteroid was 6 miles across. As it entered the atmosphere, the fireball in its wake would have been miles wide, appearing to set the sky ablaze. It impacted the earth in the Gulf of Mexico near the Yucatan peninsula. The asteroid easily cut through the water, vaporizing it, and continued into the sea floor, leaving an initial crater in the ocean floor 60 miles across and 15 miles deep. The energy of the impact was comparable to 100 million megatons of TNT. That’s 6 million times greater than the 1980 Mount St. Helen’s eruption. The flash from the impact would have been brighter than 1000 suns.

All the displaced ocean water along with tons of gravel would have come raining back down on the coast within minutes. The initial impact ejected a fireball that spread over 100 mile radius, incinerating everything in its path. In addition, 2000 mph (yes, two thousand, that’s not a typo) searing hot winds shot out from the blast. Tsunamis resulting from the impact swept over the Americas with 150 foot high waves. The impact triggered magnitude 10 earthquakes, causing landslides that sparked additional tsunamis. Note that no magnitude 10 earthquake has ever occurred in recorded human history.

The final radius of the impact crater after everything settled was 100 miles. The immediate destruction radius of the impact was about 600 miles. However, while this devastation in unparalleled in human history, it alone does not account for the mass extinction caused by this asteroid.

The debris ejected from the impact effectively set the sky on fire all over the globe. Molten rock ejected into the air, heated the atmosphere to 1200 degrees F (again, not a typo). While this temperature is hot enough to cause flash fires on its own, the molten debris also fell back to earth, causing more fires. Any animal that could not seek shelter underground or underwater would have been burned alive.

Apparently the evidence shows that the species that survived this event were ground or water dwelling. However, even a number of underground and water dwelling species went extinct. After the fires and molten rock settled down, ash and other debris remained in the atmosphere, causing months of pitch black and dropping the temperature across the globe, long enough to effect food chains and result in the deaths of entire species.

As for the theoretical Los Angeles 2 km long asteroid scenario, it wasn’t as interesting, perhaps simply because it hasn’t actually happened. The blast would annihilate not only Los Angeles, but all communities within 100 miles of the coast. A firestorm would consume much of southern California and tsunamis would hammer the entire western coast. The resultant dust cloud would cover much of the Midwest, devastating crops for at least a year. Millions of people would die from the direct effects of the impact, and millions more would suffer from resulting famine. It’s not the same as molten lava raining from an atmosphere hot enough to spontaneously combust any living creature, but I still would prefer not to experience any such thing.