The unfortunate truth is that hundreds of millions of years in the future, Earth will have used up all of its radioactive materials. And when that happens, tectonic activity will stop and magma will no longer stay hot. And when that happens, no new rock will form.

Now in an alternate Earth, the map of the 21st century looks a bit like this:

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Hanley Brand made this map with the intention of what Earth would look like if sea levels were to be reduced so substantially that all of the continental shelves are now above sea level. But what if, instead of sea level drop, this was made as a result of magmatic hyperactivity?

Here's the scenario: From 56 to 23 million years ago, magma had been on the acceleration, thickening the granitic bases of the continents and performing the ancient magic of turning basalt into granite. At the rate that the magma would have made to create all of this, would this have resulted in such a drain in the magma reserves to the point of shortening the remainder of Earth's lifespan?

  • 1
    $\begingroup$ What do you mean by "Earth's lifespan" - total duration of Earth tectonic activity? $\endgroup$
    – Alexander
    Jun 6, 2022 at 18:09
  • $\begingroup$ @Alexander Yes. $\endgroup$ Jun 6, 2022 at 21:20
  • $\begingroup$ This is normally moot anyway because I'm pretty sure the Earth's "lifespan" is longer than the sun's lifespan. $\endgroup$
    – ITM_Coder
    Nov 3, 2022 at 5:39

1 Answer 1


Radioactive decay (and momentum and gravitational potential energy) are what made the inside of Earth glowing hot.

Turning some of the more superficial basalt into granite would only:

  1. Reduce the amount of molten basalt to keep molten
  2. Increase the insulating layer keeping the heat of the core from dissipating

If the magic shabang you mention ever happened, my guess is that it would have not shortened the core life.

  • $\begingroup$ It is like how cold water can take longer to freeze into icecubes than warm water. $\endgroup$
    – Daron
    Nov 3, 2022 at 12:09

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