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Antarctica Once Abutted Death Valley
Science News has a story of strange bedfellows. It seems that Antarctica was once adjacent to what is now the American Southwest, some 800 million years ago. Earth's continents then formed a supercontinent called Rodinia, predating Pangaea by some 550 million years. "...the ratios of neodymium isotopes in the ancient sediments in the Transantarctic Mountains are the same as those in what was then Laurentia, says Goodge. Also, the hafnium isotope ratios in the 1.44-billion-year-old zircons found in East Antarctica match those of the zircons found in the distinctive granites now found primarily in North America. Finally, the researchers note, the ratios of various isotopes and elements in a basketball-sized chunk of granite found in East Antarctica — a chunk ripped by a glacier from bedrock now smothered by thick ice, the team speculates — match those of granite found only in what was southwestern Laurentia, which today is the American Southwest."
The oldest one proposed is called Columbia, existing from 1.8 - 1.5 bya.
The next widely accepted was Rodinia, existing from 1.3 bya - 800 mya
The next possible was Pannotia, but it didn't last long, only from 600 - 550 mya.
The last one was Pangaea, from 250 mya to 150 mya.
The earliest ones are deduced mainly from paleomagnetism, so there may have been earlier supercontinents that we do not know about due to a lack of rocks that old.
"My understanding would be that the actual outline of the old continents looked nothing like that and we have no way to figure out what they actually did look like."
Why so black and white? Just because we don't know every detail does not mean we have no way to figure out how the earths crust has changed over time. What you are missing is that to a large degree the continents sit in the middle of tectonic plates while the edges of the plates move over and under each other, coastline can change dramatically with the level of the oceans but this has nothing to do with the movement of plates or the location of the continent. Where continents do sit meet the edge of the plates you get mountain ranges. These together with ocean trenches mark the edges of ancient/modern collisions and seperations. Add evidence from fossils, the current motion of the plates, geological features, etc, and it gives you a resonable idea (ie: not a precise map) of what bits have moved where over time. The only thing that I know of where the gross features would be impossible to reconstruct are the land masses that have been subsumed back into the mantle, AFAIK this occurs mainly in deep ocean trenches and not in the middle of a continental land mass (eg: The bedrock in central Australia is ~4 billion years old, The Hawaian islands are an example of a long lived volcano in the middle of a plate).
BTW: Tropical glaciers still exist today but only at very high altitudes.
And did you exchange a walk on part in the war for a lead role in a cage? - Pink Floyd.
As others have pointed out, the maps tend to be drawn with modern features in place to help with orientation and recognition. In point of fact, the East Coast of Laurentia probably didn't exist until 600-700 million years ago (evidence about the exact date is a bit contradictory) when one of the fractures in Rodinia separated Laurentia from Gondwanaland by opening up an ocean called the Iapetus Sea. The Iapetus subsequently closed in a complicated series of events starting about 460 million years ago and then opened up again on a sort of parallel line in the Triassic forming the modern Atlantic. We (think) we know where the East coast of Laurentia was because there is a quite distinctive geologic boundary called Emmon's (Logan's) Line that can be traced from Newfoundland to Georgia where Iapetus sea sediments were pushed up into/onto Laurentia as the Iapetus Sea closed. There are a couple of zigs and zags in Emmons line -- one NW of New York city and one SE of Montreal -- but mostly it follows the course of the Appalachian mountains and lies a bit West of the Easternmost range of the mountains.
You can't see ANYTHING from a car, You've got to get out of the goddamned contraption and walk...Edward Abbey
Actually, the continents are different from the sea floors, and not just because of the water. They do in fact "float around like rafts" over the sea floors, creating new sea floor behind them and pushing it down below them in front into trenches. The sea floors are much younger than land surfaces for that reason.