I know the whole idea of continental drift but I’m confused on how we know what past continents look like. I’ve seen so many YouTube videos of Time-lapses of what the continents were like in a span of hundred of millions of years. But they’re always incredibly detailed and it had me wondering how we know all this. I heard people say we can get an estimate what the continents were shaped like based on what directions their moving today. But that method can only take you so far right? Are all those maps of Pangea just guesses?
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If you run the current motions of the continents backward, you can see how they got to where they are. But that only works as long as the conditions driving continental movement have been more-or-less the same.
To go back further, we have to rely on geological evidence.
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First, there’s a very obvious fact: the coastline of Africa and the coastline of South America fit together really, *really* well. Like, suspiciously well. People noticed this long before the age of the Earth or the mechanics of plate tectonics were known (plate tectonics in particular is a quite recent discovery). That’s not *proof*, but the fit is pretty good, too good to be a likely coincidence.
Second, if you map out the locations of certain fossils, you’ll find them in bands stretching across continents that fall abruptly into the sea. And if you stick Africa and South America together along the lines their coasts would suggest, you’ll find that the bands line up: a band of fossils in southern Africa continues neatly into Patagonia in the southern part of South America, and a band of fossils in central Africa extends nicely into what is now the forests of southern Brazil. If the coastlines were a coincidence, this would be an *incredibly* unlikely occurrence, since it would require many different types of fossil to all line up nicely *with the same coincidental shape* as the coastlines.
Third, the same is true of mountain ranges. Mountains in one continent that run right up to the sea align nicely with mountains of approximately the same age found in other continents. That suggests very strongly that both ranges were formed in the same event, which would be implausible if they formed at separate locations. One major example is that the Appalachians of North America neatly align with the highlands of Ireland and Scotland on the other side of the Atlantic Ocean.
Four, the magnetic fields within rocks tell us something about how they were laid down. While the Earth’s magnetic field flips now and then, it typically points to close to the North or South pole, and the magnetic fields of rocks align to that as they form. So we know roughly what angle a rock was at, relative to lines of latitude and longitude, when it formed. If you trace those angles from rocks in Africa and South America, you’ll find that they line up nicely with all the other evidence.
(I’ve mostly used South America-Africa here, because that’s the most obvious divide, but the same principles apply to North America-Europe, Antarctica-South-America-Africa, and Antarctica-Australia.)
And five, we now have a known mechanism – the drift of tectonic plates – which can explain how all these pieces of evidence came to be. Plate tectonics neatly explains mountain ranges, earthquakes, volcanoes, the shape of the continents, and all of the evidence above in a single theory, which is now the accepted model of the Earth’s geology over long periods of time.
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The maps are not exact, and the details are subject to plenty of debate among geologists and paleontologists (especially for very ancient supercontinents before Pangaea). But the broad strokes are generally well agreed-upon.
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