How are scientists able to date dinosaur’s footprints accurately?

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This post is about the recent footprints found in the dried up river bed in texas. I’m aware about carbon dating, but I thought you have to have organic material. And to add on top of that, wouldn’t the layer of earth that dates back be eroded/built upon by sediments in the river?

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4 Answers

Anonymous 0 Comments

There are two main methods. Absolute and relative dates.

Radiometric dating provide an absolute date and relative dating is possible.

Depending on the rock an absolute date may not be possible but if the rock layer they are in is near rock that can be absolutely dates then you can get a more or less idea. There are various different methods that will work in various types of rock. Like Carbon -14 it depends on what’s available in the rock. Something like Uranium -Lead dating takes the time it takes for Uranium to decay into lead to work out a time. Potassium -Argon Lead 208, Argon Argon and a host of other methods used for specific rocks.

There are mix of methods where an absolute date for the rock may not be possible but the age of the components of the rock can be found and the rock can’t be older than the older piece. Like a cake can’t be older than the age of the eggs used. Xenolith inclusions can be dated to absolute dates to help establish the age of rock without directly dating the rock in this method.

Relative dating works by using reference known dates. One method is index fossils, but this is slightly problematic as there’s always the possibility that the date range for that fossil is wrong. Now they only use very specific, previously very temporally specific fossils that are very well researched but there is always a chance it is wrong. This helps with narrowing down the range. If you can absolute date some rocks elsewhere which are missing from this site you can still use relative dates if you find something like a temporally significant find here.

Anonymous 0 Comments

ELI5 answer: Dino steps in mud, mud turns to rock and leaves footprint. Scientists find footprint and figure out who’s foot it belongs to. Based on who’s foot fits the footprint we can figure out an age.

Non ELI5 answer: Footprints like that are considered “trace fossils” as in it is a trace of the organise rather than direct evidence. Dating trace fossils is exceptionally difficult, especially so for footprints but this will depend on the material that the trace fossil is found.

By using “absolute dating” we can date the material the tracks were made in to get an idea at least of how old the rocks are. The problem with trace fossils like footprints, they are left behind in what is now a sedimentary rock and most absolute dating techniques won’t work on sedimentary rock that are that old.

In this case they would have used “relative dating” where they would figure out which dinosaur the footprints belonged to. Based on the ages that have been calculated for that specific dinosaur from other sites around the world, we can then make a pretty good guess of how old the prints are. Obviously this will only work if it’s an organism that we previously know about and have good age control on it’s position in the fossil record.

Anonymous 0 Comments

Layers of sedimentary rock are laid down in order, one on top of the other. The oldest on the bottom. The layer the Dino walked on can be estimated based on that. It’s a little like counting the rings in a tree.

Anonymous 0 Comments

Yes, the layer the footprints are in was eroded by the river. But that’s because there were 65+ million years worth of layers that the river had to cut through first. Those particular footprints. just happen to be exposed at the moment. Ones that were exposed earlier may have been eroded away already. Or there are ones that haven’t yet been exposed.

Texas geology is pretty well known due to oil exploration, so they know which exposed levels belong to which ages.
https://d32ogoqmya1dw8.cloudfront.net/images/NAGTWorkshops/intro/activities/geologic_map_texas.jpg