Look at the key element in bold above: "According to Plato's writing." In other words, you know that Plato did not invent the story because in writing the story he says he didn't make up the story.
Wait a minute here, I didn't say "I know".
Solon lived about 200 years before Plato. At the time he lived, Greece was very different from the time that Plato lived. There is very little documentary evidence from that time. Little that Solon wrote survives, and most scholars think that much of what historians later said he believed in his time really shows what those writers believed abut their own times. In other words, his reputation was being used as a a ploy to give what they believed credibility.
In Plato's dialogues of
Timaeus and
Critias, Critias is the only person who speaks of Atlantis; it is not a story told by Plato, only recorded by Plato. Critias is Plato's uncle, who lived from 460 BC – 403 BC... Solon lived from 638 BC – 558 BC. I'll have to do some research on whether Critias claims to have heard the story directly from Solon, or was it repeated to Critias by another. Anyhow, In the dialogs Critias starts his story by saying that he was very young when he heard the story. He ask for a day to recall the details of the story. The next day the circle meets and Critias begins his story.
Can you find any evidence from any writer prior to Plato indicating that Solon (who again lived more than 200 years before Plato) relayed any information about Atlantis to later generations of Greeks, let alone the details in Plato's description? Can you find any evidence in any Egyptian writings of such knowledge?
As I mentioned before, Solon traveled to Egypt and the story was told there. The Greeks were just coming out of 600 - 700 years of dark ages, so I doubt anyone, other than the Egyptians, had any written record of any prior historical events. However, the philosopher Crantor, a student of Xenocrates, who in turn was a student of Plato. Crantor actually visited Egypt, had conversations with priests, and saw hieroglyphs confirming the story or as claiming that he learned about them from other visitors to Egypt.
The Hellenistic Jewish philosopher
Philo in the early 1st century AD wrote about the destruction of Atlantis in his
On the Eternity of the World, xxvi. 141:
...And the island of Atalantes which was greater than Africa and Asia, as Plato says in the Timaeus, in one day and night was overwhelmed beneath the sea in consequence of an extraordinary earthquake and inundation and suddenly disappeared, becoming sea, not indeed navigable, but full of gulfs and eddies.
The ancient philosophers Strabo and Posidonius also believe the account written by Plato.
In short, the answer to your question is yes, outside of Plato, others have wrote about it in the distant past.
No, the story begins with Plato. The story about Solon going to Egypt is part of Plato's story. There is no accurate information from Solon coming from his own time. The first reference to his visit to Egypt comes from the Herodotus, the man called both the father of history and the father of lies. Herodotus describes the trip to Egypt in detail, but there is no mention of Atlantis. Plato, living 200 years after Solon, is the first to say that he learned about Atlantis there.
Actually, as mentioned before, it's Critias' story, not Plato's... And so what if Herodotus didn't hear of the story of Atlantis in his travels? If I visit England, someone should remind me of the American Revolutionary War? I may, or may not hear it spoke of.
Let me say further, that I'm not trying to convince you, or anyone else, of anything. I've learned through out the years, that people will believe what they want to believe. I've also learned, that for some odd reason, many people get upset and take it very personal when you start asking questions about "what they know to be true." I myself try to keep an open mind. History has been rewrote before, who's to say it won't be rewrote again?