Scientists at Stanford University have announced new evidence for a massive asteroid collision occurring in earth’s formative years, a mere 3.26 billion years ago, when our planet was just a wee babe. Not that it wasn’t accustomed to being beaten up at the playground. This was a time when the earth and other planets in our solar system were constantly under fire from asteroids and the remains of planetary materials called “planetismals” (I promise I did not make that word up). It was this kind of activity that lead to the formation of the moon around 4 billion years ago, and is referred to today as the period of late, heavy bombardment. Didn’t know our planet was so badass did you?
Since that period there have been several mass extinction events on earth caused by asteroid impacts, the most famous of all being the one and only “Dino-Slayer” of 65 million years ago. The cretaceous-paleogene extinction event (or K-Pg event) lead to the extinction of all non-avian dinosaurs and paved the way for the rise of the mammals (i.e. US!). Most scientists believe the K-Pg event was the result of the epically disastrous impact of the Chicxulub asteroid, which measured over 6 miles in diameter and left a crater in the Yucatan Peninsula over 100 miles wide. So, you know, freaking huge.
Yeah, that’s it. Pretty big right?
Well, the forthcoming evidence of this new nightmare scenario asteroid suggests that it was somewhere between 23 and 36 miles wide, leaving a crater of over 300 miles. So, basically like this…
The only problem… this crater doesn’t really exist anymore and we don’t really know where it is. Why, you ask? Well, impacts like this one happened so long ago that processes of erosion and tectonic movement have changed the earth’s surface so much that the craters aren’t evident anymore. Eh, small beans to fancy geologists. They know how to read the signs of major asteroid impacts on land formations that are still around. In this case the authors of the new study, Norman H. Sleep and Donald R. Lowe, discovered the scars of an ancient asteroid impact on a land formation in South Africa known as the Barberton greenstone belt.
The Barberton belt is known for having some of world’s oldest rocks. Besides the tell-tale fractures left on its crust, it contains minuscule spherules of vaporized rock from the impact, and concentrations of an element often found in asteroids called iridium. The study indicates that the actual impact zone was likely thousands of miles away in an ocean basin, though the evidence at Barberton suggests that the event could have permanently altered the tectonic plates- perhaps putting into motion the tectonic system that we have today.
So what does this mean about the asteroid’s impact on earth? Well, basically conjure up every doomsday scenario you can imagine and that may come close to being about half as bad as this was….
“What he means is Old Testament Mr. Mayor, real wrath of God type stuff…”
Oceans boiling? Check. Megatsunamis? Check. Planet wide earthquakes? Check. Burning hot air? Check. Ash and dust filling the atmosphere and blocking out the sun? Check. Dogs and cats living together? HA! Got you there, not really a lot of complex life on the planet yet. But does that mean the asteroid didn’t have an impact on the evolution of life on earth? No way, it’s likely that there was mass extinction of many microscopic organisms on the planet. Which was probably highly influential in the direction of our ancestor’s evolution. Just imagine what kinds of life would have evolved had such a large selective act NOT happened? Probably a bunch of riffraff…
So there you have it, some new insight into earth’s childhood. Maybe you’ll show a little more respect now that you know what it’s been through the last 4.5 billion years!
Check out the original American Geophysical Union press release for the whole story, and thanks for the images AGU!