Many people believe that Earth was one big ocean at some point in its past.

During Noah’s time the earth was completely covered with water.

There are many other examples, not all related to Noah. See here, here, here, here and so on.

Is that true?

I'd also be interested to know when this was the case, or what was the largest percentage of the Earth that was ocean at any one point.

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    I've shown notability and reopened. The general claim is that water covered the whole Earth at some point (some refer to Noah's flood, but that's unimportant). Most quotes are of religious or creationist origin, but that's also to be considered unimportant to the question. – Sklivvz Apr 14 '16 at 8:15
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    After giving a couple days to fix, I've removed the answers which were not fixed. Please take any disagreements to meta. I've opened a question: meta.skeptics.stackexchange.com/questions/3600/… – Sklivvz Apr 16 '16 at 6:07
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    Note that "one big ocean at some point" is emphatically not the same as being completely covered with water in Noah's time. We can date Noah's purported Flood pretty exactly (see Biblical chronology), and know that no such flood could have happened at that time. – jamesqf Apr 17 '16 at 5:43
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    @jamesqf The original question was unrelated to Noah. A moderator just added that as an example. – DavePhD Apr 18 '16 at 18:38
  • @Sklivvz A more-specific example of the claim, that like the original question is unrelated to Noah, is "No doubt at one time the ocean covered the entire earth. As the interior of the earth cooled it contracted, and the crust being large, sank in some places and rose above the water in others, forming continents and islands." A New Method with Geography books.google.com/… – DavePhD Apr 20 '16 at 16:51

I could not find any scientific evidence that the earth was once completely covered by water (not lava).

However, Australian scientists have hypothesized that the land share on a planet 2.5 billion years ago was only 2-3%. If it is true, then the largest percentage of the Earth that was ocean is 98%.

Also:

According to the modern scientific views, the ocean appeared 3.5 billion years ago as a result of magma degassing and subsequent condensation of atmospheric vapor. Most modern ocean basins emerged in the last 250 million years as a result of the splitting of the ancient supercontinent and the cleavage (spreading) of lithospheric plates. An exception is the Pacific Ocean, representing a shrinking of the ancient Panthalassa ocean remnant.

Translation from Wikipedia

At the same time, the oldest known rocks on Earth are almost exactly 4 billion years old.

  • Due to extensive edits and the question being reopened, I am purging all comments. Thank you for your patience on this question. – Larian LeQuella Apr 15 '16 at 0:37
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    I said it before and I'll say it again, because purging comments makes no sense: the fact you quote, while true, is irrelevant to the question of whether there was a point in time at which there was no land surface. There was no continental crust at the time the oceans were formed, so it's entirely possible that the newly formed ocean covered the entire planet. But it is also possible that part of the oceanic crust stuck out of the water and was dry. I do not know if there is a consensus on which of these is the case, hence I have not posted an answer. – Nathaniel Apr 15 '16 at 15:00
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    98% ocean coverage, if true, is still pretty close to all, at least compared to any geologically recent value. – OrangeDog Apr 15 '16 at 18:01
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    @Dawn they are true things that reveal flaws in the answer. I am trying to remember what all the removed relevant things were that many people agreed with, but as everything's been purged, the context is not ideal. – OrangeDog Apr 15 '16 at 18:21
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    It would be better if you suggest corrections/improvements. – user30557 Apr 15 '16 at 18:25

According to Essentials of Oceanography (2012) at page 13

The physical expanse and distribution of the early ocean is a matter of some controversy. Most researchers hold that masses of rock have always protruded through the ocean surface to form continents. However, some recent studies suggest that water may have covered Earth's entire surface for some 200 million years before continents emerged.

The authors of A case for late-Archaean continental emergence from thermal evolution models and hypsometry Earth and Planetary Science Letters volume 275, pages 326-336 conducted 100,000 simulations to determine the fraction of the Earth covered with water 2.5 billion years ago.

The input parameters are described by Gaussian distributions using the mean values and standard deviations listed in Table 1. From [100,000] realisations, we predict a distribution of the area of emerged land and of sea level.

The Earth was completely flooded in 9322 of the trials

The medians for [area not flooded] range between 1.79 and 2.84% of the Earth's surface.

In conclusion, the research found a 9% chance that the Earth was completely covered by water, and the best estimate was the Earth was between 97.16 and 98.21% covered by water.

Yes, the Earth was entirely ocean before any continents existed.

The continental crust started forming 3.7 billion years ago. The first "micro continents", even if they were tall enough to have dry land, would consist of islands - not a sizable barrier to make you consider dividing the ocean into different places around it. That is, even if you had some dots of land, you would not consider different parts to be different oceans.

The link above mentions the oceanic vs continental crust — but was there water covering it? Look up some dates for that: The water to fill the ocean was present at the latest by 4.1 billion years ago. So, besides being covered with oceanic crust, the Earth was indeed filled with water at that time.

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    @JDługosz your first source contradicts you: "Analyses of the approximately 4 billion-year-old Acasta Gneiss suggests that the first continents and oceans developed before the Archean." -- which means before 4 billion years ago. – Sklivvz Apr 13 '16 at 13:44
  • Due to extensive edits and the question being reopened, I am purging all comments. Thank you for your patience on this question. – Larian LeQuella Apr 15 '16 at 0:38
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    I said it before and I'll say it again, because purging comments makes no sense: this answer is the correct one, though I think it might be debated whether there were some dry regions of non-continental crust. – Nathaniel Apr 15 '16 at 14:58
  • I thought that would be good to ask on Earth Sciences SE, but perhaps DavePHD's answer gives this detail. – JDługosz Apr 15 '16 at 22:36

I think Seo Bro is on the right track, but I disagree with the confidence of his answer.

I think maybe the earth was once covered in ocean, although it's hard to know at the moment.

The two current candidates for world's earliest continent, Ur and Vaalbara were actually quite small compared to continents now.

I saw a documentary, I forget what it was called, that said that after the Earth's original ocean was formed, there was no land, except some islands, and then a process happened to create granite, and that was the start of continental crust.

You see, nowadays, we have oceanic crust and continental crust.

Oceanic crust is thin, smooth and heavy, and continental crust is thick, and bumpy, and generally light, so it floats on the earth's mantle easily.

So the show said that over time, continental crust has been getting created.

When I saw that, it made Wikipedia make sense. Wikipedia provides a history of the continents, that starts with a few small continents, and ends up with the large continents we live on today.

As for the creation of the original ocean, Seo Bro's quote might be correct that the water came from within the earth. I have, however, heard of another theory, that the water came from icy bodies from outer space, coming and colliding with the Earth in the Late Heavy Bombardment.

I'm sorry I can't provide stronger references than this, but I think if you look up this stuff in more reliable places, they will agree with what I've said here.

Some of the information contained in this post requires additional references. Please edit to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted.

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