[wnissen]

You might be surprised at how little we know about fusion. We can observe the sun, but the sun is already very hot, millions of degrees, so any unknown fusion reactions would have already happened. Nowadays we have high-powered lasers that can create laboratory-scale fusion reactions.

E. O. Lawrence's 1930 cyclotron could generate protons at roughly a million degrees Celsius. But that's a single proton stream. Good for splitting atoms but not for fusing them. You really don't know what the cross section of a fusion reaction is until you do it. The properties of matter at that temperature are just super weird. If it had turned out that there was, e.g., a carbon-carbon fusion reaction with a lower initiation, that might be enough to "go critical" and kick off more fusions, and propagate around the world. According to estimates, the Chicxulub crater was 1-10,000 degrees C. Not even the same ballpark.

https://www2.lbl.gov/abc/wallchart/chapters/11/4.html