I have often thought that the most profound time to have changed the human trajectory would have been the modern beginning of using oil in its many forms. Combustion, petrochemicals, and its profound influence on geopolitics.

So my change would be that in the very beginning of the era of wider use of oil, say, the late 1800s, that something was discovered in oil's nature that made it totally unusable. And that there was no technology that could even come remotely close to making it safely usable.

As noted elsewhere in this thread, the outcomes would still be a mixture of pluses and minuses. But it seems to me that at least there would be vastly fewer humans and that our impact on the Earth would be vastly lower.

Very interesting thread!

Saul