# Geology question **URL:** \ **Category:** Factual Questions\ **Created:** [October 15, 2008, 3:48am UTC](https://boards.straightdope.com/t/geology-question/468004 "2008-10-15T03:48:02Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Rapier42](https://avatars.discourse-cdn.com/v4/letter/r/90db22/32.png) [@Rapier42](https://boards.straightdope.com/u/Rapier42)\ **Post date:** [October 15, 2008, 3:48am UTC](https://boards.straightdope.com/t/geology-question/468004/1 "2008-10-15T03:48:02Z")
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. Thanks! ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [October 15, 2008, 4:05am UTC](https://boards.straightdope.com/t/geology-question/468004/2 "2008-10-15T04:05:00Z")
It is called the Pre-Archean or [Hadean era](http://en.wikipedia.org/wiki/Hadean). ---
**Author:** ![Rapier42](https://avatars.discourse-cdn.com/v4/letter/r/90db22/32.png) [@Rapier42](https://boards.straightdope.com/u/Rapier42)\ **Post date:** [October 15, 2008, 4:19am UTC](https://boards.straightdope.com/t/geology-question/468004/3 "2008-10-15T04:19:05Z")
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 \, 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. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [October 15, 2008, 4:27am UTC](https://boards.straightdope.com/t/geology-question/468004/4 "2008-10-15T04:27:04Z")
> [@Rapier42](#): > > he was referring to rock strata in the Grand Canyon, pointed to an area where the layers were strikingly different, called it \, That’s the [great unconformity.](http://www.lpi.usra.edu/science/treiman/greatdesert/workshop/greatunconf/index.html) ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [October 15, 2008, 5:28am UTC](https://boards.straightdope.com/t/geology-question/468004/5 "2008-10-15T05:28:41Z")
> [@Squink](#): > > That’s the [great unconformity.](http://www.lpi.usra.edu/science/treiman/greatdesert/workshop/greatunconf/index.html) [simpler expanation](http://nvcc.edu/home/cbentley/geoblog/2008/08/some-great-unconformities.html) ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [October 15, 2008, 11:35am UTC](https://boards.straightdope.com/t/geology-question/468004/6 "2008-10-15T11:35:04Z")
> [@Rapier42](#): > > 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 \, and mentioned that this particular billion-year era was missing in all geologic records across the planet. …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.😉 ---
**Author:** ![Yossarian](https://avatars.discourse-cdn.com/v4/letter/y/9de0a6/32.png) [@Yossarian](https://boards.straightdope.com/u/Yossarian)\ **Post date:** [October 15, 2008, 12:40pm UTC](https://boards.straightdope.com/t/geology-question/468004/7 "2008-10-15T12:40:43Z")
> [@Rapier42](#): > > 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. > > Thanks! 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. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [October 15, 2008, 12:47pm UTC](https://boards.straightdope.com/t/geology-question/468004/8 "2008-10-15T12:47:24Z")
> [@Yossarian](#): > > First the bad news: Geology documentaries are very often full of bad information. … 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. ---
**Author:** ![Rapier42](https://avatars.discourse-cdn.com/v4/letter/r/90db22/32.png) [@Rapier42](https://boards.straightdope.com/u/Rapier42)\ **Post date:** [October 15, 2008, 4:57pm UTC](https://boards.straightdope.com/t/geology-question/468004/9 "2008-10-15T16:57:15Z")
> [@Squink](#): > > That’s the [great unconformity.](http://www.lpi.usra.edu/science/treiman/greatdesert/workshop/greatunconf/index.html) This. Thanks, all! ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [October 15, 2008, 5:14pm UTC](https://boards.straightdope.com/t/geology-question/468004/10 "2008-10-15T17:14:25Z")
\>the Earth’s crust is not floating on a molten mantle of magma What? Then, what holds it up? ---
**Author:** ![Yossarian](https://avatars.discourse-cdn.com/v4/letter/y/9de0a6/32.png) [@Yossarian](https://boards.straightdope.com/u/Yossarian)\ **Post date:** [October 15, 2008, 5:20pm UTC](https://boards.straightdope.com/t/geology-question/468004/11 "2008-10-15T17:20:39Z")
> [@Napier](#): > > \>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. ---
**Author:** ![DrFidelius](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/drfidelius/32/3447_2.png) [@DrFidelius](https://boards.straightdope.com/u/DrFidelius)\ **Post date:** [October 15, 2008, 5:27pm UTC](https://boards.straightdope.com/t/geology-question/468004/12 "2008-10-15T17:27:52Z")
> [@Napier](#): > > \>the Earth’s crust is not floating on a molten mantle of magma > > What? Then, what holds it up? Turtles.