How Old Are White Sands NP's Fossil Footprints?

all right today i'm going to talk about a really cool study that just came out that helps us understand relative and absolute age dating techniques and how they can work together to help constrain the age of small layers in the rock record so the study that i'm talking about about revolves around some fossil footprints and these were found so these are ich no fossils so that means they're track fossils they're not fossils of the actual organism but fossils that are left behind showing that the organism was moving through an environment um and that's what's recorded these were found in white sands national park which is in new mexico in the u.s okay now white sands is a really cool place where we have big white sand dunes hence the name and the sand here is made out of gypsum so it's kind of unique and gypsum is an evaporite mineral so it forms when we have water that's enriched and this has calcium and sulfate in it and as the water evaporates it left behind the gypsum the gypsum was then weathered and turned into the sand that makes up the dunes there today now the really cool thing about these fossils is that they've been these tracks have been known since the 1930s so they were first there were some tracks that were discovered way back in the 1930s and they were really big footprints so the early people who found it thought that this might be bigfoot but it wasn't these really big fossils were giant ground sloths so these are really big big feet so leave behind these gigantic footprints and they were alive back during the ice age so they're not alive today so they're extinct so that was since then um since the 1930s thousands of tracks have been found including more of these giant ground sloths they've also found mammoth waffles and our mammoth like this big guy right here these aren't alive today but they were walking across the landscape during the last ice age and their big footprints are left behind in this layer of gypsum mud or this ancient mud they've also found ancient human footprints and that's what the really cool study was looking at today so what's interesting about these footprints um they're found around an area that once had a lake so this was ancient i'm just going to write this here ancient lake make sure i spell it correctly otero and this was a lake that was about six 1 600 square miles in size and it dried up about 10 000 years ago but before it dried up it was a lake and so we know that humans and animals tend to go to watering places and it's a good place to live around these ancient lakes but lakes themselves as water falls on this area it's going to create mud in the flats around it and that mud starts to dry out and it creates a perfect place to store footprints so i imagine you've probably maybe when you were a kid ran around without your shoes on and stepping in mud you leave behind really cool footprints and that's what happened that's where these footprints are left behind in this very interesting gypsum mug that was once around this ancient lake now the the interesting thing is we don't know exactly how old or up until now how old some of these fossil footprints are and so that's the big question is how old [Music] so some researchers actually found a perfect layer so because this is uh not an ash layer so we have i'm just going to try to draw this out here so just imagine that you find these footprints i'm drawing them in a cross section so this would be older and younger but i'm drawing the footprint sideways so you can kind of imagine them so let's see i'll try to make it more like a human footprint and they're very distinct human footprints that we see here okay and they're moving through this whole area so now we do find places where human footprints have been left behind in volcanic mud so when you have a volcano erupt it leaves this ash the ash falls out of the sky and if it gets wet it makes a really sticky mud that can record footprints ash is awesome because you can radio carbon date it or excuse me radiometrically age date it to figure out how old uh the volcanic ash is and therefore how old the footprints are because they're stored in it white sands is different because it's gypsum we can't go and do age dating on the gypsum layer itself it's just not possible but what the researchers did and this is in a journal or so it's science and it was published september 20 21 okay but what they ended up finding out is that when they they found a layer of these footprints the footprints are really cool because they have lots of footprints um so they have adults lots of teenagers and children moving through here there are like eight different horizons which means layers that have the fossils and they show 61 different individual footprints and of those they represent at least 16 different people so they can look at the size and the shape to figure out kind of which prints might have belonged to well some unknown who we don't know exactly who it was but we know that this track was made by this you know one of these people and they're crisscrossing they saw lots of movement of people going about their daily lives again really cool but how old are they well since we don't have ash researchers got really creative and they started looking through these layers and they found one set of tracks that were sandwiched between layers of rock that had seeds so these little circles are representing a grass seed an ancient seed and this is called i'll get it down here rupiah now the cool thing about this rupiah because they found it below and above the tracks they were able to use radiocarbon dating so our carbon 14 and they were able to figure out how old the seeds were below the footprints and above the footprints and the age below so the older layer was 23 000 years the rock above or the seeds above are 21 000 years so we know that the footprints because they're found in between these two layers were put down between 21 000 years ago and 23 000 years ago so that's pretty cool so the process of using carbon 14 to age date these grass seeds that's our absolute age dating technique and then we're using our relative age dating techniques to know that when we have layers that are put down horizontally the ones down below are older than the ones above so that's how we can sandwich these footprints so that's what i thought was really cool is it shows that we have relative and absolute age dating to figure out the age and further it's just awesome though this study is talking a lot about humans being present on north america so the big question is why do we care well these footprints with this age date has these people very well established in north america during the last glacial maximum so they call it the lgm so last glacial maximum and this is a time when we had huge extensive ice sheets covering north america so as you put well to get that we have colder temperatures more ice up on the continents that lowers sea level and it exposes beringia which is the land bridge between siberia and alaska so the fact that we're finding these fossils of people down in new mexico shows that they were really well established and they they could have been there long ago so the anthropologists people are quite excited about this trying to understand the migration of the people of the americas if you will and that ties it in but again today for understanding the earth it helps us by connecting an absolute age dating method with some relative age dating to figure out the age of these fossils i hope you found that as cool as i did today keep your eyes open as you read the news because geology is happening everywhere

Channel: Earth Explained

Views: 143,535

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Id: VBnysJyDg4c

Length: 9min 55sec (595 seconds)

Published: Fri Sep 24 2021