Impact!
Dinosaurs were killed by an asteroid impact on Earth 66 million years ago. This astonishing model for dinosaur extinction was at first derided as fanciful nonsense when it was proposed by Luis Alvarez and colleagues in 1980, but all the evidence shows this is correct.
What is the evidence? There are many discoveries that show this is true:
- The Chicxulub crater in Yucatán Province, Mexico (it is over 150 km across, corresponding to a 10-km asteroid)
- The impact then caused three dramatic crises:
- Glassy spherules everywhere (as the asteroid plunged deep into the Earth’s crust, it melted itself and rocks on the way, and the back-blast sent huge amounts of molten rock into the air, where it solidified into tiny, 1-mm beads that fell out for 1000 km or more around the impact site within an hour of the impact)
- Tsunami beds round the Caribbean (the asteroid hit water, and sent a huge shock wave and tsunami that battered the shores of Mexico, Texas, the southern United States, and Caribbean islands)
- Iridium spike (iridium comes from space, and was distributed round the world in dust that flew up into the upper atmosphere, and settled over land and sea a week or so after the impact)
- The glass beads-tsunami beds-iridium-rich dust sequence can be seen in many rock sections all round the impact site
Speculation –> Science
This is a great example of how a subject of speculation became scientific. Before 1980, most discussions about the extinction of the dinosaurs were based on limited data. Now, we have great rock dating of what happened, detailed rock sections showing the three processes, geophysical evidence of the crater shape and size, and so much more… read the whole story in Dinosaurs Rediscovered.