Iceland may be the tip of a sunken continent
space.com
space.com
A "nearly Texas-size continent" would be about the same size as Madagascar, and much smaller than Greenland, and we don't call Madagascar or Greenland continents.
The smallest landmass usually called a continent, Australia, is about 10x larger than Texas.
IIRC, the definition of "continent" in some contexts is not solely based on size. Continental crust is geologically different than oceanic crust, so if you find a bunch of it sunken underwater, it arguably a continent (geologically).
But it's not like there's a really solid definition for "continent" (e.g. IIRC, Europe is one almost entirely for cultural reasons).
There are such things as micro-continents (which Madagascar would fall into).
https://en.wikipedia.org/wiki/Continental_fragment
According to this article, sure it's Wikipedia, but I learned this in geography class at school, "Continents are the largest landmass of a particular continental plate"
https://en.wikipedia.org/wiki/Island#Differentiation_from_co...
By this "simplified" map of continental plates then the lower half of Central America is technically a continent:
https://en.wikipedia.org/wiki/Plate_tectonics#/media/File:Pl...
According to Wikipedia, Zealandia (where New Zealand is) is also an "almost entirely submerged mass of continental crust" that's half the size of Australia. And "geologists from New Zealand, New Caledonia, and Australia have concluded that Zealandia fulfills all the requirements to be considered a continent".
But that "simplified" map of continental plates shows how much geologists definition of "continent" differs from the usual definition. As you said, central America and the Caribbean are on their own plate. And Asia actually contains land from four "principal" plates (Eurasian, Indian, Arabian, and part of the North American plate), while Europe and most of Asia are together on the Eurasian plate.
His thesis is that there was an advanced civilization - "Atlantis" - that was wiped out by a comet impact around 10,000 BC.
I honestly don't know what to make of this book. It has rigorous research and several references and citations about the younger dryas impact hypothesis. He brings in multiple folk tales, tribal origin stories and mythologies that suggest that the comet impact and the subsequent flooding are recorded in oral traditions.
Then he goes off into the deep end with History Channel's ancient aliens style conjectures about the Pyramids of Giza and various references to "the seven sages" who bring advanced knowledge from Atlantis to reboot civilization post comet-impact.
It's totally entertaining in the same way that watching serious people talk about crazy UFO stories is interesting. And like any conspiracy theory, there is enough room to have fun thinking about how much truth could really be lurking underneath it all.
Pure fun, if you have absolutely nothing better to do with your time.
There are so many gaping holes in his theories he purposefully ignores because addressing them would require him to completely discard his profitable pseudo-scientific nonsense.
I get it though, I too went down the rabbit hole of the whole "Lost ancient civilizations" thing, but the deeper I got, the more I realized the whole notion is utterly missing any kind of real scientific underpinnings.
YouTuber / archaeologist Stefan Milo made this pretty comprehensively damming rebuttal video to Hancock's so called "Theories" that does a far better job explaining the specifics than I ever could, and I highly recommend watching it.
I just finished watching the video and unfortunately I don't buy it at all. Now Graham Hancock is clearly peddling some hard-to-believe theories, but this rebuttal video doesn't do much to refute him.
He takes the weakest possible interpretation of Graham's work and asks "where is the evidenc?" in multiple ways.
I think the same rebuttal would be stronger if he addressed why the track record of archeologists so far have been very credible and that they have a history of testing out falsifiable theories by looking for negative results. For example "we don't expect to find any evidence for human activity below this depth in this region - and look, we didn't find anything".
Graham's argument rests heavily on archeologists not doing a good job and the easiest way to dismiss him is to show otherwise. This is easy to do with Physicists looking for particles that would poke holes into the standard model for example.
I'd love to see a solid rebuttal for Hancock's theories that doesn't rest upon "consensus among archeologists" without showing why the same archeologists are credible.