from Wikipedia:
The Appalachians are believed to have been the highest mountains on earth roughly 466 million years ago during the Ordovician Period, much like (but higher than) the Himalayas today, when all of today’s continents were joined as the supercontinent Pangaea.
How do Geologists go about estimating the height of a mountain range 466 million years ago? Was the process that created the Appalachians a faster and more violent process than India colliding with Asia, therefore pushing them higher? Or is it a more indirect estimate based on their age and current height?
I’ve read somewhere that the Himalayas are very close to the maximum height a mountain range can be on Earth. Any higher and the weight of the mountain begins to crush the base.
This question interests me because I live near and have spent alot of time in the appalachians. I enjoy hiking and imagining my surroundings are a half billion years old and were once snow capped.
I’ve been reading alot about the geology of the Appalachians. They are the oldest mountain range on Earth and obviously they were once much higher than today. I just haven’t found a good explanation for the statement that they were once higher than the Himalayas.
I’ve been out of school for 15 years now, but from what I remember the Appalachians are folded mountains so they have anticlines and synclines. Since the synclines are what we can see now they can measure them and get an estimate on how big they really were.
Interesting fact in the Wikipedia article for the Appalachian Mountains:
I seem to remember “learning” in a class along the way that the large continental shelf on the East and Gulf Coast of North America is so large because it basically is the remains of the Appalachians…(and perhaps one way to measure how big they used to be) But then I know the Atlantic is far younger than the old Appalachians (especially if they were completely eroded away by the end of the Mesozoic), so maybe I misheard or it was simply wrong.
Paleoelevation is the term your’re sort of looking for. There’s a bunch of somewhat esoteric ways of getting at it, like oxygen isotopes in minerals that formed in-place, fossil assemblages and the metamorphic minerals that formed in the root of the mountain range. But I would guess they’ve inferred the paleoelevation of the Appalachians by looking at the Appalachian Basin, which is where the material that eroded inland off the range went.
The Appalachian Basin is one of the most heavily studied sedimentary basins in the world because it was (and still is) hugely important economically. They have a pretty good handle on where the sediment in the basin came from, how thick it was originally and the history of deposition and erosion. You can sort of do the same thing with the continental shelf, but estimating volume of those sediments is harder for various reasons. But having a good idea the landward portion gives you a pretty good ballpark notion of how big the mountains were originally.
Also, regarding the Himalayas, I think you may be a little confused. It has been said that in terms of prominence above the surrounding landscape, Mt. Everest is close to the theoretical maximum for an above-water mountain on made out of common continental crust rocks. But that doesn’t necessarily have any bearing on the overall average height of the Himalayan Plateau. As a bit of a side note, there is some debate about how the Himalayas are even as high as they are, because they do not appear to be in isostatic equilibrium (whereby the surface topography is balanced by a “root” of crust extending into the mantle). Since we don’t seem entirely clear on all the processes that can hold up high topography, I’m not sure if anyone in the field would really declare a theoretical maximum at this point.