(See also part 1, Tunguska below)
Powerful though it was, the Tunguska event was just a fire cracker compared to what can happen. Bigger asteroids can resist complete atmospheric breakup long enough to blow up on contact with the ground. The result is an impact crater, which can blast enough pulverized rock into the atmosphere to change the climate dramatically, perhaps for months, over the entire world. One such impact killed the dinosaurs 65 million years ago, when asteroid Dinolith slammed into the ground near Chicxulub town on the Yucatan peninsula, in Mexico. It has been argued, however, that some dinosaurs survived and live on today. We call them birds (some we call “hummingbirds”).
A much more recent and, thankfully, smaller one landed only 50,000 years old. It is about 3/4 mile in diameter, and is now billed as “the world’s best preserved meteorite impact site just minutes from Interstate 40.” In Arizona, it is owned by the Barringer Crater Co., perhaps the world’s only legitimate crater company. There are some other crater companies that will sell you craters and other land on the moon and other extraterrestrial getaways. However under established international law they do not actually own what they are selling, and so can hardly be considered legitimate. Other companies sell merely certificates of ownership to extraterrestrial craters and such, not the craters themselves, leaving it to the possessors of the certificates to try to enforce their claims of ownership. Those companies may be legitimate, but are really certificate companies, not crater companies. For those who feel that priceless and unique geological treasures should not be privately owned, even the Barringer Crater Co. is not legitimate, leaving the world without even one legitimate crater company. In any event, this crater is also unique in being the world’s most plainly named crater: its legal name is “Meteor Crater.” It is now marketed as a tourist attraction, not having the billion dollars worth of buried iron that old man Barringer hoped for when he acquired it in 1903.
The largest impact crater on Earth known with certainty is the Vredefort crater in South Africa at about 170 miles across. It was crated when asteroid Archaeoaster (“ark-ee-oh-aster”), 3 to 6 miles in diameter, slammed into Earth just over 2 billion years ago, long before the first dinosaur stepped out of its eggshell. The largest in the U.S. is Chesapeake Bay on the coasts of Maryland and Virginia. Impact craters on Earth tend to weather to the point that it is not obvious to the naive observer that they are craters. On the other hand, the moon is pockmarked with numerous and well-preserved impact craters easily visible through telescopes, because erosion from atmospheric winds and surface liquids does not happen there.
The inner solar system is populated with a half million asteroids larger than the one that struck Tunguska and yet we’ve identified and mapped only about one percent of these asteroids to date.
