the 8th Continent?

Sea levels were  MUCH lower during the last Ice Age, and when it ended, all sorts of lands were lost.  E.g., Doggerland, where the North Sea is now, land to the west of India, Beringia, which connected Asia, and North American, and so on.  Atlantis may have been one of these, having disappeared about 10,000 years ago, give or take.  Maybe; no-one really knows for sure.

Atlantis is probably nothing more than a myth. The only person to ever mention it was Plato. He heard about it from an Athenian lawyer, who heard about it from an Egyptian priest.  That's really not much to rely on. And he said Atlantis existed 9000 years before his own time. There would have been no way he could have known of such a place.

So far there has been no evidence indicating that there is a sunken continent in the middle of the Atlantic Ocean.  If Atlantis did exist then the most likely location is the southwestern coast of Spain or Portugal.  The sinking of Atlantis in a day and a night suggests that the cause was an earthquake which caused a  tsunami. Another possibility is that a landslide in the Canary Islands caused a tsunami.  Other than what Plato wrote there is, so far no other historical records to support the existence of Atlantis.  Maybe Atlantis existed, maybe it didn't.  People thought the Trojan War was a myth until Schliemann uncovered Troy so who knows what may be discovered in the future.  
Personally I like to think Atlantis did exist but am not a fanatic about its existence. 

So far only Zealandia meets the criteria to be a submerged (mostly) eighth continent.

The fact that only one person in history ever wrote about it should tell you something.  The fact that not even he bothered to write down where the hell it was should tell you something more.  The fact that every single resident of Atlantis, including all the cousins and in-laws, perished on that same unknown date should tell you the rest.

Think of it, every single resident of Atlantis died, not a single survivor.  Nobody in Greece even once said "Hey, my sister's husband is from Atlantis, he's working as a pharmacist in Athens" or "Atlantis is gone?  Damn, my cousin married a girl there, I hope he made it out".  Nope, every single person who knew anything about Atlantis (except Plato) was killed when it sank into the ocean.

And your CAPS key keeps getting stuck, just so you know.

The Path of the Higher Self discusses in some detail;
A Dweller on Two Planets is interesting about Atlantis.

No one really knows.

It did exist but is lost, not a mythical place