# How many oceans are there on earth? **URL:** \ **Category:** Factual Questions\ **Created:** [January 3, 2013, 3:01am UTC](https://boards.straightdope.com/t/how-many-oceans-are-there-on-earth/645914 "2013-01-03T03:01:28Z")\ **Posts on this page:** 7\ **Page:** 3
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [January 4, 2013, 12:59am UTC](https://boards.straightdope.com/t/how-many-oceans-are-there-on-earth/645914/41 "2013-01-04T00:59:37Z")
> [@the\_diego](#): > > An ocean has for its bottom the ocean floor, which is the basaltic crust. The Caspian and Black might not qualify, not even the Med since the Med is just a depression on the boundaries of the two colliding plates that are North Africa and Southern Europe. All three still have continental granite at their bottoms. That’s incorrect. The Mediterranean, Black, and Caspian Seas are all underlain at least in part by oceanic crust, being the remnants of the former [Tethys Ocean](http://en.wikipedia.org/wiki/Tethys_Ocean) that has nearly been obliterated by the collision of Africa and India with Eurasia. ---
**Author:** ![figure9](https://avatars.discourse-cdn.com/v4/letter/f/f0a364/32.png) [@figure9](https://boards.straightdope.com/u/figure9)\ **Post date:** [January 4, 2013, 1:27am UTC](https://boards.straightdope.com/t/how-many-oceans-are-there-on-earth/645914/42 "2013-01-04T01:27:25Z")
Two. The ocean of water and , the atmosphere - an ocean of air. ---
**Author:** ![Ignotus](https://avatars.discourse-cdn.com/v4/letter/i/ecc23a/32.png) [@Ignotus](https://boards.straightdope.com/u/Ignotus)\ **Post date:** [January 4, 2013, 3:26am UTC](https://boards.straightdope.com/t/how-many-oceans-are-there-on-earth/645914/43 "2013-01-04T03:26:54Z")
Good. I always knew you were with me , Colibri! Let’s say the deep basalt crust sets the standard of the Ocean Floor. (And I guess there are no other contenders- like, the lake Baikal? or anyone else? ---
**Author:** ![the\_diego](https://avatars.discourse-cdn.com/v4/letter/t/7bcc69/32.png) [@the\_diego](https://boards.straightdope.com/u/the_diego)\ **Post date:** [January 4, 2013, 4:21am UTC](https://boards.straightdope.com/t/how-many-oceans-are-there-on-earth/645914/44 "2013-01-04T04:21:52Z")
> [@Colibri](#): > > That’s incorrect. The Mediterranean, Black, and Caspian Seas are all underlain at least in part by oceanic crust, being the remnants of the former [Tethys Ocean](http://en.wikipedia.org/wiki/Tethys_Ocean) that has nearly been obliterated by the collision of Africa and India with Eurasia. My mistake. I didn’t look beyond the sedimentary deposits. Lots of sediments and salt domes below the seafloor made me think it was still continental crust underneath. It’s oceanic alright. ---
**Author:** ![Dr.Drake](https://avatars.discourse-cdn.com/v4/letter/d/ad7895/32.png) [@Dr.Drake](https://boards.straightdope.com/u/Dr.Drake)\ **Post date:** [January 4, 2013, 5:01am UTC](https://boards.straightdope.com/t/how-many-oceans-are-there-on-earth/645914/45 "2013-01-04T05:01:20Z")
> [@TonySinclair](#): > > I could also be wrong, but I think his point was that the continents also fit that definition. A continent is a type of island. The largest {2, 4, 5, 6, or 7} islands are usually known as continents, because of the unique properties discussed upthread (tectonic plates, canals, tradition, endemic wombat populations). We’re pretty much defining oceans by continents, anyway: between the Americans and Eurasia / Africa = Atlantic; between the Americas and Eurasia / Australia = Pacific; between Africa, Eurasia, and Australia = Indian; between N. America and N. Eurasia = Arctic; between Antarctica and Africa / S. America / Australia = Southern. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [January 4, 2013, 5:31am UTC](https://boards.straightdope.com/t/how-many-oceans-are-there-on-earth/645914/46 "2013-01-04T05:31:35Z")
Perhaps an “ocean” has a mid-ocean ridge that drives plates? ---
**Author:** ![the\_diego](https://avatars.discourse-cdn.com/v4/letter/t/7bcc69/32.png) [@the\_diego](https://boards.straightdope.com/u/the_diego)\ **Post date:** [January 4, 2013, 8:07am UTC](https://boards.straightdope.com/t/how-many-oceans-are-there-on-earth/645914/47 "2013-01-04T08:07:00Z")
^ Looks like all of them have spreading ridges, even the arctic. But basaltic ocean floor is my bet. [Previous page](https://boards.straightdope.com/t/how-many-oceans-are-there-on-earth/645914.md?page=2)