Fallen Boulder Reveals 313M-Year-Old Fossil Footprints at Grand Canyon

Maybe the low parts near water? It had to be wet to capture what appear to be claw marks.

The authors of the paper actually describe their hypothesis for how it occurred [0]. Basically perfect conditions were required to preserve them.

In short the first tracks were made in dry sand, eroded a little, moistened by fog, dew, or light rain, and then covered by dry sand again. The second tracks were made through the dry sand into the moist layer which was then crusted over with calcite and covered. Only the toe markings from the second tracks were preserved.

[0] https://journals.plos.org/plosone/article?id=10.1371/journal...

It might be something as silly as change of wind that brought dust instead of sand or maybe different type of sand.

Basically anything that covers the fresh print with a layer that is different enough chemically or physically that will then cause the layers to develop/preserve a boundary that can then break clean off millions of years later after everything is pressed/mineralized/whatever other processes happened.

In this case they are estimating the ages based upon the known ages of the geologic formations surrounding the layers of sand the tracks were found in [0][1].

[0] https://journals.plos.org/plosone/article?id=10.1371/journal... [1] https://www.geotech.hr/en/how-to-determine-the-age-of-a-rock...

There is an entire branch of geology dedicated to answering that question called stratigraphy [0]. It's hard to pinpoint exact dates but we can get a pretty good estimate (313 million +/- half a million is pretty good).

The authors describe how they determined the date in their paper [1]. In this case they know the relative age of the formation the tracks were found in (Manakacha Formation) because we know the age of the formations around it. The ages of the surrounding formations are estimated by the known ages of the fauna (other fossilized organisms) found in those formations (319 Ma below and 312 Ma above).

[0] https://www.geotech.hr/en/how-to-determine-the-age-of-a-rock... [1] https://journals.plos.org/plosone/article?id=10.1371/journal...

And the humble layman knows that this is resolved by radiological techniques being able to date things on the scale of billions of years.

For not circular methods, take a look at https://en.wikipedia.org/wiki/Radiometric_dating#Accuracy_of...

"As long as this cognitive process is acknowledged as the pragmatic basis of stratigraphy, both local and global sections can be treated as chronologies without reproach." (American Journal of Science 276:55). –J. E. O’Rourke

The paper you cited actually goes on to show why the type of dating used is as accurate as it can be. Index fossil ages have been used to calibrate radiometric dating and vice versa. Not all rock formations have radioactive elements we can use to give rocks an "absolute age" meaning relative aging often is as good as we can get.