<p>Is there some evidence for this based on gravity anomalies?  I think I know how to tell if a mountain or structure is compensated based on bougeur and free air anomalies, but this really has me stumped?  Does this somehow tie into how underwater mountains are compensated by pratt rather than airy?  </p>

CC BY-SA 3.0
2018-02-10T19:36:54.930Z
Where did you get the idea that continents sink?  Basically (and really simplistically) continents are lighter rock that "floats" around on the mantle.  Some continental rocks have been around for several billion years  http://news.mit.edu/2011/stable-continents-0106 while little if any of the ocean crust has been around for more than 300 million http://www.earthobservatory.sg/faq-on-earth-sciences/where-do-we-find-oldest-continental-rocks-and-oldest-seafloor
jamesqf
CC BY-SA 3.0
2018-02-10T20:54:47.100Z
Thanks, those links are really helpful.  This is a question my geophysics professor gave to work on over the weekend, essentially he wants me to disprove the idea that oceanic crust is really sunken continental crust.  I'm not 100% sure what he is getting at though.
spinelcity
CC BY-SA 3.0
2018-02-11T03:25:34.047Z
Perhaps the idea is that the mostly basaltic ocean crust is denser than continental rock, and this could be detected by gravity measurements?  I'm not a geophysicist, though.
jamesqf
CC BY-SA 3.0
2018-02-11T17:18:58.700Z
Counter-counter argument: [Zealandia](https://en.wikipedia.org/wiki/Zealandia).
David Hammen
CC BY-SA 3.0
2018-02-11T20:32:55.730Z
@David Hammen: However, is there evidence that Zealandia actually sank, rather than (as the link says) just having thinner continental crust than other continents, so that much of it is often below the changing sea level?  Compare for instance the area of the continental shelves that was above sea level in the last Ice Age: https://www.iceagenow.com/Sea_Level_During_Last_Ice_Age.htm
jamesqf
CC BY-SA 3.0
2018-02-16T13:31:07.517Z
I believe it's the other way around: continents are formed when they raise out of the ocean via marine or volcanic activity. (or another part of an already existing landmass) A great example of this is Florida. Florida was formed mostly by volcanoes.
Eevee
<geology><geophysics><isostasy><geodesy>
What gravitational evidence do we have to counter the idea that oceans are formed when continents sink?
spinelcity
# What gravitational evidence do we have to counter the idea that oceans are formed when continents sink?

(Asked by: username_0 on 2018-02-10)

Is there some evidence for this based on gravity anomalies? I think I know how to tell if a mountain or structure is compensated based on bougeur and free air anomalies, but this really has me stumped? Does this somehow tie into how underwater mountains are compensated by pratt rather than airy?

**Tags:** geology, geophysics, isostasy, geodesy

> **Comments:**
> **username_1**: Where did you get the idea that continents sink?  Basically (and really simplistically) continents are lighter rock that "floats" around on the mantle.  Some continental rocks have been around for several billion years  http://news.mit.edu/2011/stable-continents-0106 while little if any of the ocean crust has been around for more than 300 million http://www.earthobservatory.sg/faq-on-earth-sciences/where-do-we-find-oldest-continental-rocks-and-oldest-seafloor  
> **username_0**: Thanks, those links are really helpful.  This is a question my geophysics professor gave to work on over the weekend, essentially he wants me to disprove the idea that oceanic crust is really sunken continental crust.  I'm not 100% sure what he is getting at though.  
> **username_1**: Perhaps the idea is that the mostly basaltic ocean crust is denser than continental rock, and this could be detected by gravity measurements?  I'm not a geophysicist, though.  
> **username_2**: Counter-counter argument: [Zealandia](https://en.wikipedia.org/wiki/Zealandia).  
> **username_1**: @username_2: However, is there evidence that Zealandia actually sank, rather than (as the link says) just having thinner continental crust than other continents, so that much of it is often below the changing sea level?  Compare for instance the area of the continental shelves that was above sea level in the last Ice Age: https://www.iceagenow.com/Sea_Level_During_Last_Ice_Age.htm  
> **username_3**: I believe it's the other way around: continents are formed when they raise out of the ocean via marine or volcanic activity. (or another part of an already existing landmass) A great example of this is Florida. Florida was formed mostly by volcanoes.  

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## 0 answers

