Answer to Question #11031 Submitted to "Ask the Experts"

Category: Environmental and Background Radiation — Rocks, Minerals, and Mines

The following question was answered by an expert in the appropriate field:

Q

Does the Earth’s crust block radiation from the planet’s core? If it does, are we exposed to higher radiation levels when we are on the ocean, since the water doesn’t shield us from radiation at the Earth’s core as well as the solid land does?

A

This is an interesting question! There are a few things that are relevant—let’s tackle them one at a time.

Believe it or not, most of the natural radioactivity in the Earth is in the Earth’s crust. What’s happened is that over the history of the earth the entire mantle and crust have been turned over, recycled, and churned quite a bit. During this process the atoms that are radioactive (uranium, thorium, and potassium) have tended to move upwards, and as a result of this, virtually all of the Earth’s radioactivity is now in the continental crust, where we all live and walk. Even the crust beneath the oceans is depleted in radioactivity compared to the continents. So rather than acting as a shield, the Earth’s crust is what exposes us to radiation from this source. That said, radiation dose rates from the rocks are pretty low except in a few parts of the world. And the areas with the lowest natural radiation are the oceans (both bottom and top).

Exactly what’s in the Earth’s core is open to speculation since we don’t have any samples, but it seems pretty certain that it is primarily nickel and iron with traces of sulfur and other elements. There’s probably not much in the way of radioactive elements, but this is just a guess.

P. Andrew Karam, PhD, CHP

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