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Fallen Boulder Reveals 313M-Year-Old Fossil Footprints at Grand Canyon
- simonebrunozzi 6y agoThis is the important bit: > among the oldest tracks on Earth of shelled-egg-laying animals, such as reptiles, and the earliest evidence of vertebrate animals walking in sand dunes
- has2k1 6y agoAn interesting note is, the footprints where formed on the supercontinent Pangea.
- sradman 6y agoThe paper Early adaptation to eolian sand dunes by basal amniotes is documented in two Pennsylvanian Grand Canyon trackways [1]: > The narrow width of both trackways indicates that both trackmakers had relatively small femoral abduction angles and correspondingly relatively erect postures. They represent the earliest known occurrence of dunefield-dwelling amniotes―either basal reptiles or basal synapsids... This geological formation was from the Moscovian age (315.2 to 307 Ma) or the Kasimovian age (307 to 303.7 Ma) in the Pennsylvanian period. [1] https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0237636 https://journals.plos.org/plosone/article?id=10.1371/journal...
- thdrdt 6y agoCan someone explain how these tracks were preserved on a sand dune? As far as I know a sand dune moves constantly. I can't imagine tracks would last a day. Looking at the tracks it looks more like they were made in mud and later covered by sand dunes?
- jcims 6y agoMaybe the low parts near water? It had to be wet to capture what appear to be claw marks.
- rement 6y agoThe 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.pone.0237636#sec014 https://journals.plos.org/plosone/article?id=10.1371/journal...
- austincheney 6y agoThe presence of a layer composed of a compressed calcium based salt suggests earth that eventually became covered by ocean. Calcium deposits make for fantastic preservatives. See caliche and Llano Estecado as examples. * https://en.m.wikipedia.org/wiki/Caliche https://en.m.wikipedia.org/wiki/Caliche * https://en.m.wikipedia.org/wiki/Llano_Estacado https://en.m.wikipedia.org/wiki/Llano_Estacado
- lmilcin 6y agoIt 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.
- locustsandhoney 6y agoErroneous dating. "The intelligent layman has long suspected circular reasoning in the use of rocks to date fossils and fossils to date rocks. The geologist has never bothered to think of a good reply, feeling the explanations are not worth the trouble as long as the work brings results (American Journal of Science 276:51)." –J. E. O’Rourke
- adamjb 6y agoAnd the humble layman knows that this is resolved by radiological techniques being able to date things on the scale of billions of years.
- gus_massa 6y agoFor not circular methods, take a look at https://en.wikipedia.org/wiki/Radiometric_dating#Accuracy_of_radiometric_dating https://en.wikipedia.org/wiki/Radiometric_dating#Accuracy_of...
- Yajirobe 6y agoFrom the article: 'after an organism has been dead for 60,000 years, so little carbon-14 is left that accurate dating cannot be established.'
- gus_massa 6y agoYes, carbon-14 is only useful for "recent" samples. The next section of the article discuss other radioactive materials that have a longer half life, and are useful longer ranges.
- rement 6y ago"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.
- dutch3000 6y agohow are they dating something that isn’t there? are they dating the sand?
- deleted 6y ago[deleted]
- rement 6y agoIn 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.pone.0237636#sec016 https://journals.plos.org/plosone/article?id=10.1371/journal... [1] https://www.geotech.hr/en/how-to-determine-the-age-of-a-rock/ https://www.geotech.hr/en/how-to-determine-the-age-of-a-rock...
- Yajirobe 6y agoHow did they determine the age?
- rement 6y agoThere 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/ https://www.geotech.hr/en/how-to-determine-the-age-of-a-rock... [1] https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0237636#sec016 https://journals.plos.org/plosone/article?id=10.1371/journal...