We’ve known for several decades that the dinosaurs were most likely wiped out by a meteor impact, but ongoing research continues to discover new nuances to the overall situation. New data published in Nature Communications suggests that the dinosaur-killer hit at a steep and somewhat uncommon angle — and that the consequences for life on Earth were significant.
Most reports and discussions of Chicxulub assume that the asteroid struck at a 90-degree angle. While an easy simplification, this is likely untrue; only one in 15 meteor impacts is steeper than 75 degrees, and only 25 percent occur between 60 degrees and vertical, according to the paper. Furthermore, when an asteroid strikes at 90 degrees, three distinctive features — the mantle uplift center, peak ring center, and crater center — are all on top of one another. That’s not the case at Chicxulub. Instead, these features are staggered off-center, with the peak ring center and the mantle uplift center on opposite sides of the crater center. This indicates the impact angle was something other than 90 degrees.
The crater center is the center of the area the asteroid or comet excavated, the peak ring center is the center of the inner ring of displaced rock that forms in this type of complex crater (as shown in Lowell crater below), and the point of maximum mantle uplift is the spot where the mantle rose highest under the crust in response to the impact. After a hit like the Chicxulub impactor, the Earth would have rung like a bell for days, seismologically speaking.
Lowell Crater, Mars, with peak ring visible. Image from NASA via Wikipedia
The researchers modeled a variety of impact angles and speeds to determine what the most likely criteria for the impactor were. What they found strongly suggests that the asteroid or comet approached at a 60-degree angle, based on the remains of the crater and how the debris was distributed. The images below show the trajectory of a 60-degree impact versus a 30-degree impact.
60 degree impact. Image by Nature.
30-degree impact. Image by Nature.
At low impact angles, the center of the mantle uplift and the center of the simulated peak ring are both shifted downrange. When the impact occurs at a high angle, the mantle uplift offsets uprange, while the peak impact ring offsets downrange. The degree of offset depends on the impact angle, and 60 degrees matches the offsets we see at Chicxulub.
The “worst-case scenario” comes into play because of what the asteroid hit. The rocks underneath the Chicxulub impact site were rich in hydrocarbons, sulfur, and CO2, in part thanks to huge organic deposits left over from living things. The 60-degree impact, according to the researchers, released 2-3x more sulfur and CO2 than a 90-degree impact would have, and 10x more than a very shallow (15-degree) impact would have.
In short, we may exist today because the dinosaurs didn’t just get hit by an asteroid — they got hit by an asteroid in the worst possible way. Had the asteroid arrived moments later, or at a slightly different angle, the last 66 million years of history on Planet Earth might have gone down a very different path.
Feature image credit: NASA