The Beware of Movies! series is meant to point out some of the scientific inaccuracies of popular movies, specifically in points related to the geological sciences.
This post will point out the major inaccuracies portrayed in movies about the science of paleontology. I’m a paleontologist. This oughtta be good…
Commonly, about two seconds after I tell someone I’m a vertebrate paleontologist, they ask me what I think of Jurassic Park. Then I laugh. It’s either that or they ask me if I carry a whip like Indiana Jones. Then I snarl something about how 1) Dr. Jones was an archaeologist and 2) Indiana was the dog!
Misconceptions about paleontology: 1) Paleontologists only study dinosaurs. 2) Paleontologists study arrowheads and ancient pottery.
I’ve written a few blog posts about what can be done with isotopes from precipitation, and how that might assist us in understanding how to interpret isotopic data collected from ancient rocks and fossils. (Look here and here.) As I live here in western New York state, close to Lake Ontario, I frequently have opportunities to further study how the isotopes from precipitation (in this case Lake Effect snow) are related to the isotopes of the water that originally evaporated to make the clouds that do all the snowing.
Right now, we’re looking at a Lake Effect snow event that’s due to start sometime tomorrow, so I’m throwing together is quick and fun isotopic study that I’ll share with you when the data come in. I’ll describe it here.
As review, let’s think about isotopes in water. First, what do I mean by isotopes? The term worries people, because they immediately think of radioactive isotopes and OMG, we’re gonna die! No, it’s not like that. The word isotope just refers to the fact that some atoms of the same element are heavier or lighter than the others.
Water is composed of hydrogen and oxygen (H2O). Hydrogen comes in two types. Most of it has a mass (think of it as weight) of 1. Some of it has a mass of 2. (The hydrogen with a mass of 2 is called deuterium. It’s one of the few isotopes that has its own name.) So water is mostly made with hydrogen atoms of mass 1, but some water has hydrogen of mass 2. The water with the mass 2 hydrogen is heavier than the water with the mass 1 hydrogen.
Similarly, oxygen comes in two important isotopes. The most common form of oxygen has a mass of 16. A more rare (but not radioactive) form of oxygen has a mass of 18. Either type of oxygen can be in a water molecule, but the water with the mass 18 oxygen is heavier.
With mass spectrometry, we can measure water to see how much of it has the heavier hydrogen and the heavier oxygen. This is what I do for a living.
To get any kind of precipitation (rain or snow), water must first evaporate to make a vapor mass in the atmosphere. You can think of this as just making a cloud or a storm. In the case of Lake Effect precipitation, the water that’s evaporating is the lake itself. When the water evaporates, the lighter water evaporates more than the heavier water because, well, it’s lighter. So the cloud that you get from evaporation is isotopically lighter than the lake it evaporated from.
We measure ‘lighter’ or ‘heavier’ with isotopes using what we call ‘delta notation.’ The numbers we get are given in ‘permil’ (‰) even though they’re not a concentration. What’s important is that more positive delta values means that there’s more of the ‘heavy’ element. More negative values means there’s more of the ‘light’ element. So, if the lake has a delta value of -1‰, then the cloud should have a more negative value, like -3‰. When a cloud rains or snows, the heavier elements fall out first, because they’re heavier. If the cloud has an isotopic value of -3‰, the snow should have a more positive value, like -2‰.
The change between lake and cloud, or between cloud and snow, is called fractionation, and is controlled in part by temperature. (This means that the numbers I just gave you are completely made up.) The fractionation is also different for hydrogen and oxygen, and we measure these separately. (Hydrogen and oxygen isotopes in water do tend to vary together, but it can get pretty complex.)
As a cloud rains, it loses its heavy isotopes. If we take a cloud or storm (or say a hurricane) and take it from its water source (a lake or the ocean) and move it over land, this fractionation will go on. If no more water vapor is added, then the cloud gradually gets isotopically lighter. This means that the precipitation will also get lighter (but will always be heavier than the cloud). This process is called ‘Rayleigh Distillation,’ and is an important assumption in isotope geochemistry. Luckily, it has been shown to be a good model.
All right, let’s get back to Lake Effect snow. We’re looking at a Lake Effect event that is expected to start sometime tomorrow. We can get snow bands off of the lake that make great stripes of snow across the landscape.
What Lake Effect snow from Lake Ontario teach us?
We know that the snow will be forming from water evaporated off of Lake Ontario, so it will be useful to know the isotopic values of that water as a baseline. We have no way of measuring it isotopic values of the water vapor (the cloud) but we can find out the air temperature close to the lake surface and calculate the the isotopic value should be.
Then, we can measure the isotopic value of the snow that falls. We can collect snow that falls right at the lake (that which first forms from the freshly evaporated water) and we can look at snow that falls some distance away. We can make predictions about what patterns we might see.
Predictions:
1) Snow collected near the lake will be isotopically heavier than snow collected further away. Even though it’s only a few miles, Rayleigh Distillation should have some effect.
2) Over time, the snow collected at one location should not change in isotopic value, unless air temperature at the lake varies significantly. Because the cloud will be continuously replenished from Lake Ontario, I don’t expect to see any variability over time. The isotopic value of the lake water should not change consequentially. What can change is the air temperature, which will alter the fractionation of the isotopes (when it’s colder, less of the heavy water will evaporate). Also, colder temperatures could result in freezing of the lake surface, effectively moving the shoreline further into the lake.
It’s a pretty simple thing to test these predictions. I just need to collect some snow samples (and recruit other people to do the same). Specifically, I’ll be collecting every six hours, since I’ll be measuring snow depth at that time interval anyway. Collecting every twelve hours would probably be sufficient. I run a laboratory that has a liquid water isotope analyzer, so analysis will be easy. Once I’ve got the results, then it’ll be a quick write-up that everyone can benefit from here. It’ll be interesting to see how well my predictions hold.
Our water analyzer, Norm, analyzing waters from hurricane Sandy.
If you live nearby and think you might be interested in helping out with this little project, let me know in the comments below. The more the merrier!
UPDATE 1-21-13
After waiting for 24 hours, there has not yet been any snow. But I’m assured it’s on the way!
@paleololigo It’s coming; 1 week from tonight I think you’ll have 1-2′ on ground.Tues PM you will get a foot, Wed, Thu, Fri will see more!
The Beware of Movies! series is meant to point out some of the scientific inaccuracies of popular movies, specifically in points related to the geological sciences.
This blog post will point out the major inaccuracies portrayed in movies about the Earth’s composition and its magnetic field.
Today (January 15, 2013) I presented a Beware of Movies lecture at a local retirement community. The focus was on the Interior of the Earth, and was the topic of an earlier blog post. It was a wonderful experience. (I love doing those things!) In the process of preparing, then delivering, the presentation, I did realize that I left a few critical things out. Hence, a new blog post!
Meteorites — What do they have to do with the Earth’s interior?
One of the big problems that arises with bad geology movies is that they get the composition of the Earth all wrong. There aren’t amethysts in the mantle. Diamonds and rubies would not co-exist. We know that the mantle of the Earth is composed of mafic and ultra-mafic rocks (think back to Bowen’s Reaction Series). That means it’s mostly low-silica, high iron and magnesium rocks down there. Even deeper, we know that the core is composed mostly of iron and nickel.
As we stand on the Earth’s surface, such minerals and rocks are rare. It’s easy to think that most of the rocks of the Earth should be felsic things like granite, with tons of quartz. This is simply not the case.
But why? How can we make the assumption that the mantle is mafic and the core is iron and nickel. We know some of this because there are a few places on Earth where mantle rocks have been exposed at the surface (usually due to tectonic events). We can hypothesize some compositions based upon how seismic waves refract through the body of the Earth (seismic waves travel at different rates through different materials).
We can make some assumptions about the overall composition of the Earth based upon studies of meteorites. We assume that the bits of rock and dust that collected all those billions of years ago to form our beloved planet formed from the same bits of rock and dust that make up meteorites. If you take a meteorite and grind it up, you find it to be of mafic composition, with low silica, and high concentrations of iron, magnesium, and nickel. Some meteorites are almost pure nickel and iron. Others are more rocky. This is assumed to be the starting point for the Earth’s composition.
A Chondrite – a very primitive stony meteorite. Photo by H. RaabA polished surface of an iron meteorite – photo by Opsoelder
Over millions of years, these mafic pebbles that came together to form the planet fused, and then underwent a process called ‘differentiation,’ which is just a fancy way to say ‘the heavy stuff went to the middle.’ Thus, the nickel and iron are at the core of the Earth, surrounded by the mantle of mafic rocks. Felsic rocks, like granite, tend to be light and naturally ‘float’ to the surface, which is why they are what we usually see in the rocks around us!
Magnetism — The Earth isn’t exactly a giant bar magnet, but it’s similar.
Here’s the neat thing about the core. It’s iron and nickel. Iron is a conductor. If you have an electrical current, you have a magnetic field. And voila! The Earth has a magnetic field.
The core is divided into two parts, the liquid outer and the solid inner. The mantle is also solid. Because the Earth rotates, flow is set up in the Earth’s liquid outer core. With that flow, and a little nudge, an electric current is set up. The flow is thought to be in several isolated cylinders surrounding the solid inner core. This is where the ‘bar magnet’ analogy fails, because each cylinder has it’s own field, and these combine to form the magnetic field of the Earth. This is referred to the geomagnetic dynamo.
Geomagnetic dynamo. All this is happening in the core.
Because of the dynamic nature of flow in the core, the magnetic pole never quite lines up the the Earth’s rotational axis. In fact, the magnetic poles move around quite a bit, sometimes even reversing themselves (though this takes more than a single human’s lifetime). There are lots of questions regarding how the magnetic field forms and how it might reverse itself, and is an active field of research in geophysics.
Beware of movies! The basis of the entire movie “The Core” is that the flow in the liquid outer core has stopped, thus causing the Earth’s magnetic field to fail. If we did lose the magnetic field, there could be repercussions, however, the magnetic field on Earth has gone essentially to zero multiple times in Earth’s history. Every time the magnetic poles reverse themselves, the field goes to zero first. While there is some evidence that this might have caused problems for certain single-celled organisms, large animals have not been affected. The cataclysms that are shown in the movie would not be expected. So don’t worry.
Premise: Could the awkward defeat the hulking in one zillion BC?
Caveman has got to be one of my all-time favorite movies. I liked it when I was a kid, because it was just plain silly. As I got older, I liked it because it had Ringo Starr in it (I was a Beatles fan – I guess I still am!). As an adult, I’m entertained by the subtext. (Zug-zug!) And as a paleontologist, I am wildly entertained by all the inaccuracies.
It’s comedy, so of course it’s fraught with inaccuracy. A lot of it is intentionally blatant. That’s what makes it funny. Because this movie is billed as comedy, any intelligent person knows better than to believe anything in it. I’ll just point out the paleontological silliness and warn you that if you haven’t seen this movie before, there are lots of spoilers ahead!
It opens with a big guffaw. One zillion B.C. it reads on the screen. Zillion isn’t even a proper number, but it is certainly much larger than a billion, thus exceeds the known age of the Earth (even back in 1981).
Setting— Everything about where the movie was shot, down to the tar pits, says California. Well, cavemen were not kicking around in California. They were in Europe.
Dinosaurs and humans— What were they even doing there? Dinosaurs and humans never co-existed. They missed each other by at least 60 million years.
The Dinosaurs themselves— Only two dinosaurs were depicted. One was a lizard-y guy with spikes on his back and tail and a big pointy horn. This guy also had chameleon-like eyes that moved around this way and that. He also had a sprawling stance (his legs out to the side like an alligator). This was clearly made up. This could be a take on the original interpretation of Iguanodon, but I think it was just made up for the sake of the show.
The original (now known to be inaccurate) reconstruction of Iguanodon – Photo by mugly on Flickr
The other dinosaur was Tyrannosaurus rex (I assume). This version of T. rex is a nod to the original interpretation of the dinosaur, with the body held vertically and the massive tail resting on the ground. This is in marked contrast with the interpretation of T. rex in Jurassic park, which itself is totally different from modern depictions of the beast. These days, T. rex is seen as a fleet-footed predator that held its body horizontally and its tail straight out behind. The modern view of T. rex also includes feathers.
The Tyrannosaurus of Caveman is a talented dinosaur, however, able to emulate howling wolves, crowing roosters, and hooting owls. It’s actually worth a bit of a chuckle to think that the crowing and hooting aren’t so far off from possible, given that modern birds are thought to be the closest living relatives to dinosaurs, especially theropods like T. rex.
The pterosaur and the giant egg— Pterosaurs and humans never co-existed either. Though not dinosaurs, pterosaurs lived during the same time and went extinct at the same time as dinosaurs. The giant egg was clearly too large to have been laid by the pterosaur that we see flying around in the movie, but it sure lends itself to a hilarious sequence of events.
A nearby ice age…— This is hilarious because we know it ain’t possible. An ‘ice age’ is a time period, not a place, and certainly, no-one is going to walk from the desert to a frozen wasteland in one day. Nevertheless, the snow beast is adorable and you just have to feel for him. Maybe he was just trying to make friends.
My favorite part of this movie has nothing to do with paleontology. I love the bit where Atouk’s little tossed together tribe has an impromptu fireside music, song, and dance fest. It just makes me happy.
Pink diamonds are curious. First, they’re pink. Second, they change color depending on the wavelength and the intensity of light that hits them. They stay pink, but are different shades.
A pink diamond
Scientists are attempting to figure out what gives these diamonds their pink color. In many minerals, it is impurities that cause the color. In pink diamonds, it actually appears that the colors change from electrons changing their energy state due to the light being shone on them.
The Mars Curiosity Rover has made some great discoveries in it’s short tenure on Mars. It recently tried out it’s Hand-Lens Imager to get a close look at the individual grains that make up a rock. One of the grains was rather transparent, and some have thought it looks like a flower.
Spoiler: It’s not a flower. My guess is that it’s probably just quartz. I see mineral grains like that in sedimentary rocks all the time. Nevertheless, it’s pretty cool. Finding quartz like this can tell us something about the history of Mars as a planet.
There’s also a little line of rocks near the lower center of this image. NASA scientists are calling it “Snake River.”
From Mars Curiosity Rover. “Snake River” is in the lower center of the photo
Curiosity will likely visit Snake River to have a peek at what it really is. Given how it appears to cut across layers, it is likely that it formed after the main layers in this photo. Understanding what it is, then, can also teach us something about the geologic history of Mars.
This is just nice. A pod of killer whales had found themselves cut off from the open sea and trapped in the Hudson Bay when sea ice blocked their route out. Before you say ‘well, couldn’t they have just gone under the ice?’ remember that whales are mammals and need to breath air. If their path is completely iced over, they can’t breathe. Whales can drown.
Trapped Killer Whales
Luckily, warmer temperatures and winds seem to have shifted the ice, making it possible for the whales to escape. This story has a happy ending!
So, why is this in here? Oceanography is part of the earth-sciences for one. And for two, the reason why the whales were in Hudson Bay so late in the season could potentially be due to the effects of global warming. Perhaps we’ll see more events like this in the future.
If you’re familiar with Twitter, you’re familiar with the concept of the ‘hashtag.’ A hashtag is used to mark a tweet so that it can be collected with tweets on a similar topic. For example, there’s a new television show coming out called “The Following.” If I want to see what other people are tweeting about The Following, I just look for the hashtag #thefollowing. The pound symbol at the front of the tag is what distinguishes it as a hashtag.
When I teach, I devise a hashtag for my class: #UREES101 for the introductory geology class and #UREES207 or #UREES270 for my upper-division paleontology courses. Students can use the hashtags to tweet questions and answers (or whatever they want) that’s related to the course and anyone who searchs for the hashtag can find their tweets.
The other day a hashtag was started that’s been a delight to follow: #overlyhonestmethods. People using this hashtag post about the scientific methods and techniques used in their research, as if they were writing them up for a professional paper, but being totally honest about why they did what they did. You can look at the posts here, through tweetchat. You don’t need to have a Twitter account to enjoy them.
There are a couple of good blog posts already out there too:
The main reason why these are so funny is that there is truth in all of them. Yes, there was a globetrotting postdoc in our lab for a while, and washing shave cream from beard hairs is no fun. That data was never published, but if it were published, we’d find a better way to describe why we selected our sample subject.
It’s also true that we use 14 injections because it worked, and I didn’t want to keep fiddling with the method. I would probably leave out the last bit about being tired of messing with the water analyzer.
So many things that go on in labs are done for convenience. But, that does not make the science wrong. We always outline what exact our methods were. If the eyeballs sat in the drawer for 18 months, we report that. We just leave out the bit about how we forgot about them.
We lay out what we did, not necessarily the ‘why,’ unless it would have a profound effect on our results. It doesn’t matter that we had a convenient traveling postdoc. All we do is report that there was a human subject who had to shave anyway. Who cares if it’s 14 or 5 injections? When we run our analyses, we get the same results as other labs. We’re good.
What #overlyhonestmethods provides is a tongue-in-cheek behind-the-scenes look at what life as a scientist is really like. Some of the posts are clearly jokes, others are absolute truth. But all reflect the reality, and fun, of being a scientist!
Premise: What if we could clone dinosaurs and made a theme park around them?
You were probably waiting for this one. I had to do Jurassic Park. I’m a paleontologist. It’s a rule, right?
When Jurassic Park came out, I was in my fourth year as an undergraduate (I’d been a senior for a while already, and wouldn’t graduate for at least one more year), studying both geology and biology. I was going to be a vertebrate paleontologist, and I was pretty sure I was going to study dinosaurs. (I never have studied dinosaurs, but I did become a vertebrate paleontologist. 50% is pretty good, right?)
I never did see this in the theater. I saw it a year later when it came out on video. I watched it the evening of the day that I took the GRE exams. Yes, exams in the plural. This is back when there were only two dates a year you could take the GRE and it was a hand-written test. I took both the general and the subject exam in one day. I was fried that night. I remember laughing at the cute dinosaurs while my roomates and friends fell on me in terror.
Since then, this movie has been a popular one to watch with the various geology clubs I’ve been associated with. It’s full of problems with both paleontology and biology. I’ll try to stick to the paleontology problems.
The bottom line is this: We’re probably not EVER going to see cloned dinosaurs. Now, maybe we can do some genetic engineering and get dinosaur-like animals from modern birds, but that’s about it.
I’m only planning to review the first Jurassic Park movie. The others are based upon accepting the assumptions from the first, so there’s little point in considering the others (with the possible exception of the character Robert Burke, from the second movie, The Lost World).
PORTRAYAL OF PALEONTOLOGY: Oh, goodness, it’s wrong. Just wrong. The setting, the outcrops, were all right, but what the science looked like is wrong.
Exposing the fossil: 1) I have never been to a fossil locality where a brush was all that was needed to expose a fossil. Additionally, paleontologists tend NOT to expose fossils as they dig. They only uncover enough so that they can determine the exent of the the fossil. Then they trench around the specimen, keeping as much rock as possible in place. Once a trench is dug, and the fossil is still encased in rock but now sitting on a pedestal, paleontologists will jacket the fossil with plaster and take it into a laboratory to fully remove it from the rock. Never, never, never do we do such detailed preparation in the field. The specimens will be ruined, if not by people walking on them (or helicopters landing nearby), but by the elements. It takes time, sometimes years, to get a fossil out of the ground. The more that remains encased in rock, the better.
Seismic: Not that I fully understand how seismic works, but I’m certain that a single shotgun blast isn’t going to yield an image by which a paleontologist can recognize the half-moon shape of the dinosaur’s wrist bone.
The fossil itself: Y’know, sometimes a complete fossil is found in its death pose, but usually even then some of the bones are out of place. To find as single complete specimen is unusual. To find two, both laid out perfectly, is so unlikely that I could not suspend reality to accept that part of the movie. And something as big as the ‘Velociraptor’ that they portray would almost certainly have damage or distortion somewhere.
Science and funding: Apparently Hammond, the creator of Jurassic Park, has been providing Drs. Grant and Sadler with $50,000 a year to fund their research. That might seem like a lot of money to you, but in reality, that’s chump change. Just saying. Research efforts like those are expensive, especially if Sadler and Grant are getting any salary from it. I’ve submitted some ‘cheap’ grant requests for less than $50,000 per year. That covers my research expenses and only two months of my salary. Most programs need much more than that.
THE DINOSAURS: They did pretty good with the dinosaurs, all things considered. I’m glad that Spielberg isn’t going to go all “George Lucas” on these movies and fix them up though…
Velociraptors and the relationship with birds: What Alan Grant in the movie says about the relationship between birds and dinosaurs is mostly true. Most of us in the paleontological community refer to birds as ‘avian dinosaurs.’ We have chickens and I am always calling them my little dinosaurs. What Dr. Grant says about ‘raptor’ meaning ‘bird’ may also be true, but let’s face it, that’s not evidence that birds and dinosaurs are related. If I start calling a donut a banana, does that make the donut fruit? No. (Besides, ‘raptor’ actually means ‘thief’!)
Speaking of Velociraptors: The true ‘Velociraptor’ is a little animal that would stand about hip-high on most adult people. The veolociraptors in the movie were enlarged to make them look cooler. When Spielberg came up with this, paleontologists said, ‘Well, ok. Sure. It’s a movie. Go ahead,’ basically accepting that this was going to be wrong. But at about the time that the movie came out, a huge new species related to Velociraptor was discovered in Utah, and was named Utahraptor. The velociraptors of the movie could be Utahraptors in real life. And the paleontology community breathed a collective sigh.
Inferences about behavior: Velociraptors hunt in packs. Gallimimus ran in herds. This is arm-waving. This is literary license. This is not something that can be inferred directly from the fossil record. We don’t know exactly how these animals interacted. We don’t know how they behaved. We can observe modern birds and assume that dinosaurs might have behaved in similar ways. Nothing more.
Inferences about perception in dinosaurs: Apparently, Tyrannosaurus can’t see you unless you move. Dr. Grant knew this somehow. OK, we don’t actually know this. There are animals that can only see objects if they move quickly, like some frogs, but we can’t possibly know if this is true with dinosaurs. By the same token, we don’t know if velociraptors can stare you down, either. If we’re going to base this inference on their nearest living relatives, however, I’m pretty sure that T. rex could see you even if you were sitting still.
Modern understanding of dinosaurs: If this movie were to be made today, the velociraptors would most likely be completely covered with feathers. The T. Rex would also have feathers, probably. Any of the theropods would be feathered. Now, I’m not sure about the sauropods – the big Brachiosaurus– I’m sure someone else knows.
By the way, Dilophosaurus:Dilophosaurusdoes not have the neck frill that is shown in the movie, and it didn’t spit poison, either.
Cloning: So this is biology, and a bit of chemistry. 1) DNA wouldn’t last. Over 65 million years it would degrade so much that it would be unrecognizable. 2) Frog DNA? If they were clever, they’d use bird DNA. Seriously, a FROG?! Now if we really wanted dinosaurs, what we need to do is study the anatomy of dinosaurs and compare that with birds as adults and embryonically. Then let’s try to make the embryo of modern birds develop to make a dinosaur-like skeleton and see what we get… This, I think, is within the realm of possibility, but the ‘dinosaur’ we’d get won’t be any dinosaur that ever walked the Earth!
Females turning male: Actually, such things are possible. In many vertebrates, the temperature of the eggs during development will determine the sex of the young when they’re born. Equally possible, though not mentioned, is parthenogenesis, wherein a female simply gives birth or lays eggs without fertilization. The babies are clones of the mother. This is known in many species of lizards. It’s a stretch, but it’s possible.
I could go on. There are several little details in the movie that I found annoying, but these are the big ones (or so I think). I’ve got other movies to watch and review…
Quadrantid. Photo by Brian Emfinger in Ozark Arkansas, January 2, 2012
The Quadrantids are a meteor shower that happens in January. They seem to come from an area in the sky between the handle of the Big Dipper and the head of the constellation Draco.
(source: EarthSky Communications, Inc.)
Alas, by the time this is published, the peak will be just past, having been Wednesday night into Thursday morning. Plus, the waning moon (and all the snow where I live) make it difficult to actually observe this meteor shower.
In the Pilbara region of Australia are some of the planet’s oldest rocks, dating back to about 3.4 billion years ago. In these rocks are various evidences for ancient life, including textures (like minute strands connecting to each other in a network similar to that of modern bacteria) and geochemical tracers. Yes, folks, there be isotopes there!
Metabolic processes in bacteria result in an isotopic signature wherein there is more ‘light’ carbon (carbon-12) than ‘heavy’ carbon (carbon-13) than would be expected for a limestone that formed without bacteria present.
Strelley Pool in the Pilbara, where 3.4 billion-year-old fossils have been found. Photo: David Wacey
What’s important is that finding these bacteria in such ancient rocks might suggest that the Earth’s atmosphere had oxygen in it a billion years before we previously thought. Oxygen in the atmosphere has had a profound effect on both the evolution of life on Earth and as well as it’s geologic history.
This is just cool. Who knew snowflakes were so complex? In light of all the snow we’ve received of late, this gives me something to look for in the next snowfall.
I’m a member of Litopia, a self-proclaimed “Writer’s Colony” on-line. It’s actually a great place to go and hang out with other writers and learn the trade.
Recently, a discussion thread came up about what it takes to become an expert. It was linked to this post.
Importantly, it made the point that the transition from novice to expert was marked by preferentially focusing on negative feedback over positive feedback.
Here was my reaction:
Expertise is a funny thing. For me, in my field (which is isotopic analysis of tooth enamel from fossil mammals), becoming an ‘expert’ isn’t something that I sought to do. I just wanted to do the best I could because my own research depends upon this kind of analysis. I don’t feel like an expert – I know that there’s tons of room for improvement. (But maybe this goes to the point about how experts focus on the negative more than the positive.)
But one day, about a year ago, it happened. I got the first e-mail I’d ever gotten that said something to the effect of “We have these enamel samples that need analysis, and we’ve heard you’re the best.” After I scraped my jaw off the floor, I told them that I could analyze their samples and there you go… Since then I’ve gotten similar e-mails from people all over the world and from students who want to study with me.
I guess I’m an expert.
What makes me an expert? Getting out there and getting noticed is important. So, not all experts are introverts. I mean, I guess I could be an expert and introverted, but who would know? What would it get me? Naw, I get out there, go to meetings, use Twitter and blogs, and talk about what I do. Other people notice and they decide I’m an expert.
Maybe being an expert isn’t something that you decide. Maybe it depends upon the perceptions of other people. And if enough other people – especially those that you yourself would call experts – are calling you an expert, maybe it’s true.
The Beware of Movies! series is meant to point out some of the scientific inaccuracies of popular movies, specifically in points related to the geological sciences.
This post will present some basic information about geologic time, how we know how old things are, and how movies often get these things wrong.
How do we know the order in which geologic events happened? And how do we know exactly when they occurred?
Uniformitarianism. This is an important concept used throughout the geological sciences. The short definition is “the present is the key to the past,” meaning that the processes that we observe on the modern Earth are identical to processes that occurred in the Earth’s past. Mountains exist today because of the motions of tectonic plates, thus ancient mountains also formed due to the interactions of plates.
This concept is useful for much of the Earth’s history, but might not be applicable to all of it, so it should be used with some caution. At least for the most recent 600 or so million years, it’s a safe assumption. Older than that, some important conditions on the Earth were different. One thing that is true, however, no matter how old of rocks we observe: Chemistry still works the same. Chemical reactions behaved the same 10 billion years ago as they do today. This is very important later on…
There are two basic ways of assigning ages (or dating) in the geological sciences: Relative and Absolute (or Numerical). Relative dating is used to place geological events in order of which came first, second, third, etc. Relative dating does not assign any ages (like ten thousand years ago) to events.
We’ll begin with relative dating, as this is the basis upon which our geologic time scale was originally developed.
There are six important principles used to assign an order to geologic events. Many of these apply especially to sedimentary rocks. Many of these will seem very, very obvious:
Principle of Superposition – When looking at a pile of rocks, the oldest rocks are on the bottom. Because rocks don’t just float in space with big gaps below them.
Principle of Original Horizontality – When sediments are deposited, they are deposited in horizontal layers. They’re flat. Thus, if we see rocks that are tilted in any way, we can assume that they were tilted after they were deposited.
Principle of Original Continuity – Rock layers are deposited over wide areas, not just in the one place where we see them exposed. We assume that a rock layer in one area is continuous with similar rock layers in other areas, even if we don’t see the direct connection. This is one of the most important principles needed to understand the development of the geological time scale.
Principle of Cross-Cutting Relationships – If there is a fault in a rock, or an obvious erosional surface, then we assume that these features occurred after the rock was deposited. That makes sense, because you can’t fault or erode something that does not yet exist!
Principle of Inclusions – If there are two rock types (rocks A and B) next to each other, and one (rock A) contains pieces of the other (rock B), then the rock containing inclusions of the other rock must be younger. Rock A is younger than rock B in this example.
Principle of Baked or Chilled Contacts – When magma comes into contact with pre-existing rock, reactions happen. The pre-existing rock is much cooler than the magma, causing the magma to cool rapidly and crystallize (making a chilled contact). At the same time the heat of the magma heats up and bakes the pre-existing rock, resulting in a baked contact. A baked rock is older than the igneous rock in contact with it. A chilled rock is younger than the rock it sits against.
Using these principles we can place geological events in relative order. We can trace rocks from one area to another and compile all the rocks in an area, and even on a continent into relative order. It is based upon this that the geologic time scale was developed. The divisions of the geologic time scale (like the Jurassic Period) get their names from the area in which rocks of that age were first described (like the Jura Mountains). Some divisions are also named based upon the types of rocks that characterize that division. The Cretaceous Period gets its name because many of the rocks are composed of chalk. The Latin word for chalk is “creta.” Using relative dating methods much of the Earth’s rocks deposited over the last 600 million years have been put in order.
The Geologic Time Scale
We can then add to this fossils with which we can determine a fossil succession using the principles above. It is from this that much about the evolution of life on Earth is understood.
Biostratigraphy is the use of fossils found in a rock to assign a relative or absolute age to that rock. Biostratigraphic units do not depend upon rock type and are thus defined according to the presence of a particular organism (an index fossil) or a complete fossil assemblage. Biostratigraphy is often used to correlate rocks of similar age but different rock types.
It is through principles of relative dating and biostratigraphy that we know that dinosaurs and humans have never co-existed.
Absolute (Numerical) dating is a means by which we can assign an number age to a rock or a fossil (or a geologic event). The method that most people have heard of is radiometric dating. To understand this, we have to talk a little about chemistry.
The chemical elements come in many forms. Some are stable and some are unstable. The unstable ones are also called radioactive. Some elements can come in multiple forms, some stable and some radioactive. The difference is in how many neutrons are in the nucleus, or what isotope the element is in. Carbon, for example, has three isotopes: Carbon-12, carbon-13, and carbon-14. Carbon-12 and carbon-13 are stable. Most of the carbon in the universe is carbon-12. There’s a little carbon-13, and even less carbon-14. Carbon-14 is radioactive, however. It doesn’t stay around forever. At some point it decays (or self-destructs), which is why radioactive elements are so dangerous.
Carbon-14 breaks down into Nitrogen-14, an electron, and an electron antineutrino, which sounds pretty awful. (And it is, if it happens inside your body! Those little extra bits can cause damage, which can lead to cancer.) Other radioactive elements break down (decay) in similar ways. The original element (in this case, carbon-14) is called the ‘parent.’ What’s left behind (Nitrogen-14) is called the ‘daughter.’ The decay of the parent into the daughter products occurs over a specific period of time, called the half-life, which varies from parent material to parent material. For carbon-14, the half-life is 5,730 years.
The half-life is how long it takes for half of the parent material to decay into the daughter product. Here’s an important thing about half-lives, however. This does not mean that after two half-lives, all the parent product is gone. With each half-life, half of the parent product decays. You never really get rid of all the parent material, though there does come a point where it is so small that it becomes impossible to measure.
Half-life number
Percent parent material present
Percent daughter product present
0
100
0
1
50
50
2
25
75
3
12.5
82.5
4
6.25
88.75
Radiometric dating uses this relationship to assign ages to rocks. One need only to measure the relative amounts of parent material and daughter products in a rock and know the half-life of the parent material in order to calculate the age of a rock. Different parent materials have different half-lives ranging from days to billions of years. A scientist will use the parent-daughter system that works the best for the age of the rocks their interested in. Here are a few examples:
Parent-Daughter
Half-life
Carbon – Nitrogen (radiocarbon dating)
5730 years
Potassium – Argon
1.25 billion years
Uranium-238 – Lead-206
4.47 billion years
Uranium-235 – Lead-207
704 million years
For all of these, there are caveats. Firstly, it is important that all the materials being dated actually originally contained the parent material and has not lost any of the daughter product. This can be a problem for potassium-argon dating, for example, because argon, as a gas, can escape. Radiocarbon dating is only good to about 40,000 years before present, before there is so little of the parent material left that it no longer can work.
It is also important to realize that for all of these methods, time zero (or ‘now’) is actually not right now in 2013. It’s actually 1950, which is when the methods were first established. For most radiometric dating methods, this doesn’t matter a whole lot, but for radiocarbon, it can be problematic. Nothing younger than 1950 can be dated using radiometric carbon.
Beware of movies: In the movie Time Cop, with Jean-Claude Van Damme, there’s this shipment of gold that gets transported from the past into the future. This gold is radiocarbon dated (so they say) which informs the time cop agency that it was stolen from the past. Two problems: 1) There’s no carbon in gold. What exactly did they date? 2) If the gold came forward in time, via time machine, it should seem brand new. It should not date to the past. Unless somehow, radioactive decay speeds up in the beaming forward process.
Other radiometric dating methods:
Detrital Zircons: Most of the methods described above are best used to assign ages to igneous rocks. Only radiocarbon dating really works well for sedimentary rocks (but even then, is only useful back to about 40,000 years before present). Radiometric methods can be used to assign ages to sediments when applied to ‘detrital zircons.’ Zircon is a mineral that forms in igneous rocks as they cool and can be dated using the uranium-lead methods noted above. These zircons are very resistant to weathering and become part of sediments that form new sedimentary rocks.
Zircons can be isolated from sedimentary rocks and dated, which gives the age of the igneous rock that they came out of. From this, we can determine where the sediments came from. We also know that the sedimentary rock cannot be older than the youngest zircon that’s in it. Thus, we can derive a maximum age for the sedimentary rock, which can be useful to know.
Fission-track dating: When radioactive elements decay, they leave trails of damage (or tracks) in the matrix of a crystal. These little trails are obvious under the microscope and most often form from the decay of uranium-238. Counting these tracks can be used to assign an age to the mineral and thus the rock that they came from in ways similar to detrital zircon analysis.
Some other absolute dating methods:
Thermoluminescence (TL) dating is used to determine how long a mineral (and the rock that it is in) has been exposed to sunlight. As the mineral is heated, to emits a weak light signal, which is proportional to how much sunlight it was exposed to and therefore how long it sat on the surface. This can tell us how old a material is (like an archaeological artifact) or how long a surface (like a river terrace) has existed.
The use of cosmogenic nuclides for dating surfaces has also come to prominence of late. As it happens, cosmic radiation bombarding an exposed rock surface can cause the appearance of new elements that wouldn’t be there otherwise. A scientist can measure the amount of these so-called cosmogenic nuclides and assign an age to an exposed rock. This can be used to, for example, assign ages to the advances and retreats of glaciers.
There are other methods used by scientists in assigning ages to rocks and fossils, or the parts thereof. For example, one could simply count rings!
Dendrochronology is also known as tree-ring dating. Most trees have annual growth rings which can be used to count years from the initial growth of the tree to its death. If the tree is still alive, one can correlate events down to the exact calendar year. Dendrochronology can help us study paleoclimate and paleoecology, and has been used to calibrate radiocarbon ages.
Sclerochronology refers to the study of growth lines in the hard tissues of animals and plants. Clams show growth lines, as do corals. Some teeth do as well. These growth lines aren’t necessarily annual and may be annual, monthly, fortnightly, tidal, daily, and smaller increments of time. Study of these can help us understand the biology of ancient and extinct organisms.
Ice cores also have annual layers, due to yearly cycles of dust. It is possible to count the rings in ice cores that go hundreds of meters down and study ancient climate patterns, calibrated to precise years, using other geochemical methods. This is how we know much about global warming, glaciations, and climate changes.
Beware of movies: Actually, this is something they got right in “The Day After Tomorrow.” Ice cores are commonly used to measure the concentrations of greenhouse gasses in the Earth’s past atmosphere. They use layer-counting to get the ages right.
Some methods used for dating depend upon comparing patterns of change with similar patterns derived from rock sections of known age.
Magnetostratigraphy is a technique used to date sedimentary and volcanic rocks. The Earth’s magnetic field has not always been such that the north end of the compass needle points toward the north pole. The field has reversed itself many times, and these reversals have not been regular. Scientists can go out and collect rock samples through a series of rocks and measure which way the magnetic poles were pointing at the time the rocks were deposited. This pattern is then compared with the ‘geomagnetic polarity time scale’ for the Earth (which has ages assigned to it). Where the patterns match gives an age for the rocks.
Chemostratigraphy or correctly termed Chemical Stratigraphy is the study of the variation of chemistry within sedimentary sequences. Much like magnetostratigraphy, variations of particular chemical markers also provide useful time markers. For example, the Paleocene-Eocene boundary (~55 million years ago) is defined by a huge spike in the amount of carbon-12 in the Earth’s atmosphere, which is recorded in the rock. Chemostratigraphy can also be used to track environmental changes, since chemical markers change when climates and environments change.
This post has covered most, but not all, of the potential methods by which geological units and events might be dated by geoscientists. If there are other methods that you’ve heard of, comment about them and I can explain those too.
Penny Higgins - Storyteller • Artist • Scientist 