Geology question

What is the term for the prox-billion year period missing from the geological record? My laptop wasn’t near when it was mentioned in a PBS show, and now I’ve forgotten it.


It is called the Pre-Archean or Hadean era.

Thats not what the geologist called it - he was referring to rock strata in the Grand Canyon, pointed to an area where the layers were strikingly different, called it <insert term here>, and mentioned that this particular billion-year era was missing in all geologic records across the planet.

I didn’t see the term he used in that Wiki article.

That’s the great unconformity.

simpler expanation

…except it’s not always the same time period, or the same duration that’s missing in different places. And there are places (Greenland, for ex.) that preserve a full Precambrian/Cambrian strat sequence, I believe. But anyway, I can’t think of any billion-year span after the Cryptic that doesn’t have a stratigraphic prescence somewhere in the world.

I think this is another example of American Exceptionalism, myself.:wink:

First the bad news: Geology documentaries are very often full of bad information. For example, no matter what any documentary on volcanoes or plate tectonics would have you believe, the Earth’s crust is not floating on a molten mantle of magma.

Second the worse news: This documentary also lied to you. Extraordinarily large unconformities do, indeed, exist everywhere. My backyard, for instance, consists of a layer of modern dirt unconformably sitting atop Ordovician limestone, so there’s 400 million years missing right there. However, the 1.7 Ga to ~500 Ma unconformity is not universal, which is a good thing because I quite enjoy visiting (for instance) the 1.2-1.0 Ga Blue Ridge Mountains.

Agreed, but …

I suggest that should read "First the bad news: [Insert any topic here] PBS / Discovery shows are very often full of bad information. Gee whiz sound bites trump accuracy or nuance every time. And despite the vocabulary, the target is a 6th-grade education level.

This. Thanks, all!

>the Earth’s crust is not floating on a molten mantle of magma

What? Then, what holds it up?

Brittle solid (lithospheric) mantle, underlain by plastic solid (asthenospheric) mantle, underlain by solid mantle (mesosphere), underlain by a liquid outer and then a solid inner core.

In its weakest state, the mantle might be well described as a silly-putty-like rock–but rock, nonetheless.