Looking at Craters.
Lessons and studies on Earth.
All these points have something in common aside from the fact that they are all craters. They all have different causes. But how can we tell?
At the turn of the century, many hypotheses had been proposed and there was a lot of debate in the scientific community to how craters were formed.
Meteor Crater, Arizona
Anecdotally, the idea of concentrated volcanic activity (Ring of Fire) was proposed in the 19th century by a navigator and person likely familiar with maps.
"They [the Japanese Islands] are in the line of that immense circle of volcanic development which surrounds the shores of the Pacific from Tierra del Fuego around to the Moluccas." (Matthew Perry, Narrative of the Expedition of an American Squadron to the China Seas and Japan, 1852-54,Introduction, Section I, "Name, Extent, and Geography")
However, a few questions had to be answered first. If some craters had an impact origin, how would that differ from volcanoes? Some physics principles needed to be applied to help solve this problem.
Notice during the collision the projectile (impactor) and surface become liquefied due to intense heat and pressure. But where on earth could we find such an explosion?
Fortunately (or unfortunately) and some very explosive tests had recently been conducted. Scientists had also recently synthesized some minerals using very high pressures in the laboratory and these same minerals were found by Shoemaker and Chao at atomic test sites in Nevada around 1960. It was seeming less likely that a volcano was responsible for some of these craters.
But there were problems! How could such large rocks travel through the atmosphere without breaking up? Where would these rocks have come from? How could we get accurate readings on the ages using radioactive decay? It wasn't a done deal. Lots of debate continued.
