Until the 1980s, most scientists believed that noncatastrophic geological processes caused the extinction of dinosaurs that occurred approximately 66 million years ago, at the end of the Cretaceous period.
Topic
Why did the dinosaurs go extinct at the end of the Cretaceous period? Competing scientific theories about the cause.
Framework
Old / New (with an element of Present Debate between theories)
Main Point
Currently, the volcanic-eruption theory best explains dinosaur extinction and related evidence, providing a better account than either older sea-level-drop explanations or the meteorite-impact theory.
The "Most Valuable Sentence" is at the start of paragraph 3:
P1: The Original View – Sea-Level Drop Theory
Most scientists used to believe dinosaurs died out due to noncatastrophic events such as a big drop in sea level, which changed the climate and caused extinctions.
P2: Meteorite-Impact Theory Emerges
This long-held view was challenged in the 1980s after scientists found lots of iridium in a clay layer from the time of the extinction. Since iridium is rare on Earth but common in meteorites, some researchers proposed that a massive meteorite impact changed the climate and wiped out the dinosaurs.
P3: Newest Theory – Volcanic Eruption
More recent evidence points instead to a huge volcanic eruption in India. The eruption released lots of carbon dioxide, possibly driving the climatic changes that killed the dinosaurs. The science behind it involves "diapirs" (blobs of hot rock from deep in the Earth) erupting as lava.