In Robots and Empire Mandalamus said that Earth would be radioactive within 20 decades (e.g. 200 years). But in Pebble in The Sky, it was said that people still were on Earth after 9000 years! Why so?

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    – Politank-Z
    Oct 12, 2017 at 4:36
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    The Earth has been radioactive for the past 4.5 billion years. The question is how radioactive it is in Pebble in the Sky.
    – Mike Scott
    Oct 12, 2017 at 5:46
  • @user14111 - Show don't tell.
    – Valorum
    Oct 12, 2017 at 8:16
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    Radioactivity is not Magic Omnipresent Instant Death™. You — @Daniel287leo — is radioactive... 100 Bq per kilogram of weight. So as Mike Scott said: it all depens on where the radioactivity is and how much of it there is. The dose — not "the existence of" — makes the poison.
    – MichaelK
    Oct 12, 2017 at 8:52

1 Answer 1


Pebble in the Sky says that while much of Earth's surface is radioactive, there are some safer patches left in between where humans can still live. I don't have the novel with me now, so I don't know where it says that, but the review in Jenkins' guide says “The Earth of the future is a patchwork of normal soil and land so contaminated with radiation that it glows”.

You should also know that there are some contradictions between the different Asimov novels about the radioactive earth. Jenkins' guide for Robots and Empire explains the retcons done by that later novel.

the final and most official reason for why the Earth became radioactive. The radioactive Earth features as a plot element in the three “Empire” novels, Pebble in the Sky, The Stars, Like Dust—, and The Currents of Space, and in all three, it is attributed to nuclear war. This was a common expectation in the early 1950’s, when these books were written; it was only later that Asimov realized that from a physics perspective, it was unreasonable to think the Earth’s crust could become radioactive as a side effect of such a conflict. With the additional perspective of nearly forty years, Asimov felt a need to provide a more rational explanation for this phenomenon, and does so here.

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    Notably Asimov (along with Sagan, Pohl and others) was part of a contingent of Scifi writers who made a conscious decision to overplay the potential dangers of a nuclear conflict, repeatedly attributing global death to "nuclear winter" and insisting that even a small exchange would leave vast tracts of land uninhabitable.
    – Valorum
    Dec 17, 2019 at 7:56
  • @Valorum mind that in part this was because they were unaware (as was everyone) of the long term effects of nuclear war. We now know that within a relatively short time even an area as badly contaminated as the Chernobyl exclusion zone can become habitable again, Hiroshima and Nagasaki were thriving within a few short years of the bombs falling too. In the late 1940s and early 1950s the idea was still that a large scale nuclear war could contaminate the entire planet for thousands of years.
    – jwenting
    Dec 17, 2019 at 10:52
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    @jwenting - no, they were fully aware of the consequences, they just intentionally made things sound worse in order to change public opinion.
    – Valorum
    Dec 17, 2019 at 11:12
  • @Valorum they weren't aware of the fact that conditions would return to pretty normal within years or decades after a massive release. They did know a small localised release like the airbursts over Hiroshima and Nagasaki would do that but it was generally assumed (and many misinformed people still think that) that anything at the scale of Chernobyl or larger will leave the affected area uninhabitable for tens of thousands of years (numbers still seen in many places about the Chernobyl exclusion zone, where by now people are living full time).
    – jwenting
    Dec 17, 2019 at 11:35
  • Hence the correction Asimov himself made in later editions to the idea that the earth was "made radioactive" by some device placed on the surface by robots. He had to correct himself there when it became general knowledge that that's simply not possible.
    – jwenting
    Dec 17, 2019 at 11:37

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