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CrustalTrudger t1_ixwd7nu wrote

Broadly speaking, the accuracy will decrease the further back in time you consider. This is primarily because the completeness of the geologic record as preserved in rocks decreases as a function of age (though not necessarily linearly), but also because uncertainties and/or errors related to various assumptions that are made to construct paleogeographic maps also increase as a function of age. Thus, the level of accuracy is pretty different for a paleogeographic map of the last glacial maximum (~24,000 years ago) compared to the early Cambrian (~530,000,000 years ago) and so on, but not necessarily easily quantifiable.

Within a given map, there will also likely be portions that are much more certain than others. It's worth considering the primary datasets we use to construct paleogeographic maps and what each dataset provides in terms of information. The base for virtually all paleogeographic maps are plate tectonic reconstructions, i.e., at a given time, where individual tectonic plates were, what shape they approximately were, where were their continental and oceanic components were, and what rate and direction they were moving. A variety of data informs these reconstructions, including paleomagnetism (which allows us to reconstruct paleolatitude for locations at a given time), a variety of geophysical data (it's increasingly common to use seismic tomography to reconstruct subducted slabs and "undo" subduction to aid in reconstructing ocean basins), and other geodetic data for more recent reconstructions (for recent reconstructions, the current long-term average plate rates can be extrapolated backwards reliably for 10s of million years). In addition to tectonic reconstructions, the type rocks of a given age in a location can also provide context, e.g., rocks that are diagnostic of near shore depositional environments provide context that at the time those rocks were deposited, the coastline was near that location, etc. What this means is that for most paleogeographic maps (at least within the Phanerozoic, and into portions of the Proterozoic) the broad locations of continents and their first order shapes will be broadly correct and probably in roughly the right location (in the sense of latitude and longitude). In certain places on these continents, there might be higher levels of certainty of the location of the coasts and things like major rivers based on the rocks that are preserved. Similarly, large mountain chains will be approximately in the right place, but many of the details of them (e.g., their exact widths, heights, etc) will be only relatively constrained. Lots of fine scale details would not be preserved, some of which might certainly impact the utility of maps for navigation, so things like smaller rivers (and even some large rivers) and small to moderate sized islands (so things the size of Hawaii, etc) would generally not be preserved so a paleogeographic map would not include it, and again, more so the further back you go.

Finally, when considering paleogeographic maps, it's also important to realize that there is a fair amount of artistic license taken in many cases. A good paleogeographic map will use as much of the available data to constrain as much of the paleogeography as possible, but there will still be a lot of unknowns so choices have to be made. Different people making paleogeographic maps take different strategies for how to make some of these choices. You can compare some commonly used sets of global reconstructions, e.g., those from Christopher Scotese and those from Ron Blakey, to get a sense of the variability. Without a doubt, Blakey's maps are much more aesthetically pleasing and he does a huge amount of work to make sure they're as accurate as they can be, but he also takes a lot more license to make things always look complete and like "real" landscapes (even when that completeness is effectively made up). In comparison, if you look at especially old time slices in Scotese's maps, they look more like blobs on the globe, which is not as pretty, but more accurate in terms of the level of certainty we have with respect to the actual paleogeography.

In short, the level of accuracy will broadly scale with how far back in time the period that is being reconstructed, with paleogeographic maps reconstructing periods further back in time being less accurate than more recent times. Within a time slice, some features will be much more certain than others where as some features will be effectively made up depending on the available data for that time period (and the preceding and following time periods). All of this means that we can't really quantify the accuracy of these maps (and we can't ground truth them either), but depending on the level of "navigation" you had in mind and the time period in question, they could be used to navigate to some degree. Broadly, if you trying to get from one major landmass to another by boat, most all of them would probably be good enough (at least within the last few hundred million years). If you were trying to navigate over land, there would probably be a lot of fine scale details that you would have no idea existed based on the map. Further back in time, even navigation by sea would become a bit more tricky as the probability of a semi-large island chain being in your way (that's not on the map, because it was not preserved in the geologic record) goes up.


TheRealPopcornMaker OP t1_ixwopzz wrote

Super detailed response thanks so much. So broadly speaking the maps could be used to navigate between landmasses and know when to expect mountain ranges, open plains and deserts up to around 500 million years ago?


haysoos2 t1_ixy6hsy wrote

Assuming you could figure out where you were on the map. That might not be as easy as it would seem. Getting a reasonable approximation to latitude wouldn't be that difficult, but beyond that there's not going to be any landmarks to tell you which continent you are on.

If it's in the Cenozoic or even parts of the Mesozoic you might get some biogeographic information from flora and fauna, but that's going to be sparser, and require some pretty specialized knowledge the further back you go. Those flora and fauna might even be your only real clue as to which time period you are in.


_AlreadyTaken_ t1_ixwwwsp wrote

How do they generally determine lat and long? From geomagnetic data?


CrustalTrudger t1_ixx6rl2 wrote

Paleolatitudes can be determined from paleomagnetism. Paleolongitude will more be an outcome of tectonic reconstruction.


DoubleDot7 t1_ixxid8i wrote

That's a great response. One thing to add: sea levels rise and fall over relatively short timescales, geologically speaking, which can greatly affect coastal map shape.

For example, 40,000 years ago, during the last ice age, sea levels were lower. Thus, there was solid land between Siberia and Alaska (Beringia land mass), and the British Isles and the Netherlands. Our current coastal regions were inland regions, and what is now submerged land was once the coast. In some areas, such as southern Africa, this could mean that the coast was several hundred kilometers further out than it is today. Islands such as New Zealand would have been bigger and possibly connected, too.

On the other hand, if sea levels keep rising, we may have to remove parts of Florida, New York, California and many island nations from maps over the coming decades and centuries.


CrustalTrudger t1_ixyxy4z wrote

Yes, though broadly changes in eustatic sea level are one of the things that we attempt to account for when making paleogeographic maps and as mentioned in the original answer, depositional environments can provide some context to the location of coastlines, etc. That being said, the point is valid in that paleogeographic maps tend to be amalgamations of time periods, i.e., at the finest scale we might make a paleogeographic map that represents the "average" of a few tens of thousands to few million of years of time and certainly within that you would expect a decent amount of sea level variation. All and all, a paleogeographic map would give you a rough approximation of things and would be better than nothing, but yeah, you would need to expect it to be pretty wrong at times.


Due_Avocado_788 t1_ixxoa33 wrote

The article you linked says this bridge is theorized to be in effect just a few thousand years ago. That's super interesting


FlounderOdd7234 t1_ixyuvk5 wrote

Best article of the day. No records available so up to experts like you. Love learning new things✨💯👍🥇


hypnosifl t1_ixztwbq wrote

Great answer! Are there any sources (including textbooks or academic papers) that show paleogeographic maps with varying levels of detail in a single map, based on which parts of the map (particular sections of coastline etc.) we can reconstruct in more detail from present-day evidence and which parts we only know more schematically? The Christopher Scotese maps do get more blob-like as you go back further in time but each map seems fairly uniform in the level of detail.


Columbus43219 t1_ixx19ny wrote

I love this question because it started a ball rolling in my head. No GPS... no lighthouses, the star charts would be off, the moon would be closer... the ocean currents were different... magnetic north was in a different place... sea levels were different...

I'd be starting from scratch.


PatrickKieliszek t1_ixxbped wrote

We could work out the star charts to an accuracy where they would be useful. Only unpredictable thing would be the addition of some stars that have died in the last 500,000 years.

Those shouldn't be hard to screen out.


skribe t1_ixxfl2s wrote

You'd probably need to bring along your own breathing apparatus too. IIRC 500 million years ago oxygen levels were about a fifth of today's levels.


masher_oz t1_ixxtjr3 wrote

Looks like longer than 0.5 Ga ago, there's less oxygen in the atmosphere than there is now.


skribe t1_ixxuzmq wrote

Isn't that what I just said?


imVision t1_ixz7s2b wrote

OK, but you’d need to bring in like a suit full of oxygen because the atmosphere only contained about 20% of the oxygen that today’s atmosphere has


thetarget3 t1_ixz9qg7 wrote

You can calculate your latitude fairly easily by tracking the sun's shadow at noon every day until midsummer, or until it returns again if you're in the tropics. Longitude would be really hard though.


Beware_the_Voodoo t1_ixz5265 wrote

I dont see how it's possible to accurately answer this question. If they could say how inaccurate the current maps are they could have made maps that were accurate to begin with.

The best anyone could say is that the current maps of that time period are the best estimations that could be made with all available evidence. Which is exactly what they are saying.


Willben44 t1_ixz87og wrote

I mean, say you knew that there was a certain variance in the estimates of where things were back then you could have the intuition to answer. If it’s high, then our maps wouldn’t be very useful (though there is a probability of it being exact) and if low then they could still be useful.


CrustalTrudger t1_ixzhsbn wrote

> If they could say how inaccurate the current maps are they could have made maps that were accurate to begin with.

It's very possible to know something within a given uncertainty, still be able to quantify that uncertainty, but not be able to completely eliminate that uncertainty. If we take for example the paleomagnetic measurements underlying many paleogeographic reconstructions, it is definitely possible to estimate the uncertainty, and propagate that uncertainty into uncertainty in paleogeographic locations (e.g., Heslop & Roberts, 2020). The extent to which that uncertainty can be reduced will be fundamentally limited by both epistemic (which we can reduce by collecting more data) and aleatory uncertainty within the paleomagnetic measurements. Additionally, there will be a fundamental limit in terms of how much we can reduce the epistemic uncertainty because of the limited availability of preserved rocks. Not all steps in paleogeographic reconstructions lend themselves to as direct uncertainty estimation as the paleomagnetic components, but it's not fair to say that there is no way to characterize uncertainty in these products.