[jeremyjh]

> Someone's got to explain to me how this was even remotely plausible.

You need to understand what a nuclear chain reaction is. https://en.wikipedia.org/wiki/Nuclear_chain_reaction

> We've had orders of magnitude more energetic events in earth's history

It isn't about energy. There was never an unbounded nuclear chain reaction of anywhere near this magnitude on the planet before Trinity. A large asteroid impact doesn't cause a nuclear chain reaction at all. The moon impact melted the entire crust but didn't cause a nuclear chain reaction.

In fact, the only chain reaction that happened at all before Fermi's experiment in 1942 - that we know of - was in Oklo (now Gabon) about 1.8 billion years ago. We didn't learn about that until 1972, and anyway that was more like a controlled reactor pile and it only happened because there was so much more Uranium 235 so early in the Earth's history.

The event at Trinity was completely different because so many neutrons were released at exactly the same instant. They had good reasons to be very confident in their models and calculations, but they were not 100% sure, and as TFA points out, the blast was several times more powerful than most models predicted.

[dredmorbius]

Worth noting that the along with other such events, the Giant Impact Hypothesis (a/k/a the Theia Impact) now thought to have created the Earth-Moon system had little traction until the 1970s, wasn't seriously discussed until the 1980s, and so far as I recall wasn't widely accepted until more recently, possibly the 2000s / 2010s, when I'd first encountered it.

As with other aspects of Earth's history, what's possibly surprising to younger readers here is just how much of Earth's history and the evolution of the Solar System has been uncovered recently. The far side of the Moon was unseen by humans (save for a few percent through lunar wobble / liberation) until the mid-1960s, and wasn't accurately mapped until 1969 --- a version of that map decorated my own bedroom wall as a child, and the story of that map's creation is amazing in itself, see "Race To The Moon with Richard Furno" <https://web.archive.org/web/20090129220141/https://kelsocart...> and <https://web.archive.org/web/20090130150935/https://kelsocart...>.

Close observations of other planets only began in the 1970s and is still fairly thin, though long-duration missions to Jupiter and Saturn have been impressive, though recent. The Jupiter Juno probe mission is still ongoing, having begun in 2016, and the Saturn Cassini-Huygens mission reached its destination in 2004 and culiminated (with a "grand finale" plunge into Saturn's atmosphere) in 2017.

The age of the Earth itself wasn't established until 1956, and at the time of the Trinity tests was still estimated as between 1.6 to 3.0 billion years (the presently-accepted age is 4.54 +/- 0.05 billion years). Plate tectonics wasn't accepted as the principle theory of terrestrial geology until the late 1960s. I've recently seen that this occurred between Neal Armstrong's flights on the Gemini and Apollo manned space programmes, the latter of course being his famous first footsteps (by man, that we know of) on the Moon.

But yes, as others are quite correctly noting here, there's been a huge advance in human knowledge within the span of living memory on all matter of related questions: nuclear reactions, fission, fusion, age of the Earth, major events within Earth's history, its own formation, the forces driving its evolution, and more. Looking back with the lens of the state of knowledge in 2026 is highly deceptive.