# When and how would Earth's history diverge if uranium/plutonium weren't present?

Let's imagine an Earth clone devoid of naturally occurring fissile materials—and, for comprehensiveness' sake, also devoid of fertile materials like thorium and americium that could be used to produce fissile isotopes artificially.

I suppose the first part of the question is: Could we have gotten to the 1930s or so without significant deviations? I.e., is there any under-appreciated but crucial role that these elements played in the formation of the earth, the biosphere, human civilization, etc.?

And second: what then? Obviously the end of WWII and basically all of world history thereafter would be radically altered. But geopolitics aside, what impact would this have on science and technology? Could it be as simple as, nuclear weapons and nuclear power would be impossible, while the rest of human technological progress would proceed unimpeded? Computing, telecommunications, spaceflight (minus the plutonium-based RTGs)? Even particle physics? How might this "gap" function in the context of our broader knowledge of radioactivity, stellar fusion, etc.? Would scientists have a well-developed theoretical understanding of what fissile elements are and what powerful/destructive properties they have?

Open-ended bonus question just for fun: assuming the above is roughly possible, what might happen if the plucky, naïve denizens of Earth-2 one day landed on Mars-2 and found a big ol' mess of uranium and plutonium there?

• Welcome to Worldbuilding SE! While this is certainly an interesting question, it will likely be closed for one of several reasons. It is too broad: it says "given this change hundreds of years ago, what are all the ways in which history would change?" which requires very, very long, very involved, answers, which will cover a scope of completely different ideas. Additionally it is too opinion based: Everyone will have completely different ideas as to what would happen, and there will be no objective way to decide who is "right" when selecting an answer. – Zxyrra Nov 29 '16 at 22:19
• @Zxyrra ...really? I'm new here and I'm not trying to stir anything up but I'm at a complete loss as to how this is any broader or more opinion-based than tons of other questions I see on here – Oscillare Nov 29 '16 at 22:44
• Alternatively you could break this into "Are radioactive elements necessary for life", "What physical features are dependent on radioactive elements", "What are non-radioactive solutions to nuclear technology" etc – Zxyrra Nov 29 '16 at 22:57
• This question is not too broad; though it might be written confusingly. The core question is "at what one point in time would history diverge if uranium were not present in significant quantities in earth's crust." That way we can sidestep issues about primordial heat and provide a single answer. – kingledion Nov 30 '16 at 1:40

Well for one thing we would not have any tectonic activity any more, or if it does it would be significantly weaker, as the core and mantle would have long since cooled down and solidified. which also means a much cooler atmosphere. You would not have a warm planet with liquid water not on the surface anyway. You would have an ice ball or at very least Io's big brother. Life would likely have never made it out of the oceans much less to people. A large portion of the earth's heat stems from radioactive decay material.

en.wikipedia.org/wiki/Earth's_internal_heat_budget- thank Rob for the source.

• Interesting reading: en.wikipedia.org/wiki/Earth's_internal_heat_budget – Robᵩ Nov 29 '16 at 22:32
• I don't understand how this answers the question asked. – Vincent Nov 29 '16 at 23:24
• Sorry, it answer the formation of the earth question, you would not have a warm planet with liquid water, You would have an ice ball. life would likely have never made it out of the oceans much less to people. – John Nov 29 '16 at 23:36
• @HDE226868 Regarding earth's heat; from this paper, fig 7, you can see that internal heat generation is very significant to maintaining earth's internal temp; without it you can project out the exponential heat decay of the primordial earth and how much would(n't) be left now. From this paper, Th:U:K heat ratio is about 4:1:1; given the half-lives in an exponential decay we can integrate to get a total lifetime contribution since formation of 3:1:2.5 (Th:U:K). – kingledion Nov 30 '16 at 2:03
• Since those three have dominated decay since $^{129}$I, $^{10}$Be, and $^{26}$Al decayed (about 50-100 million years in), we can say that about without Th (as mentioned by author) and U we lose 2/3 of internal heat generation over the last 4.5 billion years. I think that would significantly change the earth. Also @John; Thorium is fissionable, but not fissile. – kingledion Nov 30 '16 at 2:07

# History diverged in 1896

The history of Uranium can answer this question. The element was identified in 1789; and isolated in metallic form in 1846. Neither of these is very significant.

In 1896, however, Henri Bequerel discovered radioactive decay while experimenting with phosphorescence of uranium salts. If uranium had not been available, it is unlikely he would have made this discovery at this time and history would have significantly diverged.

Here is another twist. Before radioactive decay was understood to generate heat there was a solid belief that Earth couldn't be older than 80,0000 - 160,000 years old because it would have cooled to the point that it was uninhabitable. Once radioactive decay was discovered it became understood that earth could be millions even billions of years old which increased support for Darwin theory of evolution which at the time required an old earth to make sense. Many of our scientific theories today are the direct result of the discovery of radioactive decay. Without that discovery our fundamental understanding of the universe would be stunted.