Category Archives: Science

Introducing Friday Headlines

Friday Headlines is something I do in my introductory geology course to make Fridays more interesting and to keep the topic of the course relevant to the students. I put together a short PowerPoint presentation (10 minutes max) and tell them about two or three events in the geological sciences that have happened in the last week.

These events can be global happenings, like an earthquake or volcanic eruption; they could be the interesting findings of a freshly-published paper; or they could be some grand new discovery from NASA, like ice on Mercury or organic material on Mars. I’ve talked about global warming, peak oil, the arrest of geoscientists for incorrectly predicting earthquakes, and the Anthropocene.

What ever I choose, it is something interesting to the general public (thus, my students) and relevant to the geological sciences. My goal is to show students that things happen in the geosciences all the time, so that they understand that what I’m teaching them is actually useful in the real world.

Friday Headlines also make coming to class on Friday a bit more interesting. Students seem to like it for the change, as do I. A standard lecture every day can be pretty dull, even for the instructor.

I’ve enjoyed doing Friday Headlines during the fall semester for the last three years now. I’ve decided to take the concept a bit further and make it a recurring post in my blog. It’ll ensure at least one blog post per week (with the only possible exception being during the field season when I might not be near a computer), and should help me and my followers stay on top what’s happening in the geosciences and remember why geosciences matter.

Tomorrow I’ll post my inaugural Friday Headines article. I hope you’ll enjoy them as much as I do!

Bad Geology Movies: Earthquake, 1974 – can we even predict earthquakes?

Earthquake

1974

Charlton Heston, Ava Gardner

Premise: What would happen if a massive, magnitude 7.0 or greater, earthquake hit Los Angeles?

I bought this movie for cheap somewhere, assuming that it would be an excellent “Bad Geology Movie.” I couldn’t imagine that Hollywood would get an earthquake right.

It turns out that this movie is a typical 1970’s disaster film with an all-star ensemble cast. There was very little attempt at real science in the movie, so I don’t have a lot to say.

I do have one major point to make about this film, regarding the prediction of earthquakes. The film opens with a graduate student accurately predicting two foreshocks of the massive quake that takes out L.A. In fact, the student predicts the enormous quake as well. By some strange miracle, the mayor of L.A. is willing to mobilize the National Guard based on this prediction. The earthquake happens and chaos ensues.

This would be an amazing scenario. It would be fantastic if we could accurately predict earthquakes. But the fact is that we cannot. Not even close.

What’s worse, is that because of the political climate, even if a scientist thought he or she could predict earthquakes, they would be reluctant to say anything. It’s a miserable situation.

The characters in the film note that an incorrect prediction could be disastrous to people’s faith in science. You don’t want to cry wolf, as it were. Equally, a prediction of no earthquake, followed by a violent quake would be just as bad. People would demand to know why they weren’t warned. So what do we, as scientists, do?

For one thing, we always include probabilities on our predictions. Perhaps we only raise warnings if we think there’s a greater than 50% chance that an earthquake will happen. But even if the probability is only 10%, a quake could still happen. What then?

We also have to consider the evidence that we’re using to make these predictions. Often they’re based on historic data (how often have earthquakes happened in the past) with a little bit of new geophysical data (like sensitive GPS systems). We really don’t have enough adequate data at this point to make accurate predictions at all.

Still, people are rational, right? They understand that such predictions are impossible, right? We like to think that, but the truth is, most people don’t understand this. And the likelihood that people will be sympathetic to the plight of the scientist after a huge, unpredicted earthquake is pretty small.

Such is what happened in 2009 near L’Aquila, Italy. Italy is a tectonically active region, frequently hit with small earthquakes. There were a few strong earthquakes leading up to a magnitude 6.3 quake that hit on April 6th of that year. The town of L’Aquila was leveled and 309 people died.

Though there had been strong foreshocks in the area prior to the main quake, local geoscientists contended that the chances for a major quake were small, and the town was warned but not evacuated. After the earthquake, 6 geologists and 1 government official were put on trial for involuntary manslaughter, for not having adequately warned the citizens of L’Aquila, which resulted in the large death toll. In October of 2012, all seven men were sentenced to six years in prison.

Well, if this is what happens when you try to make any predictions in geology or the earth sciences, then I’m going to stay mum if there’s been any natural disasters. When Hurricane Sandy hit, I got a call from a local reporter who wondered if I would comment about how the hurricane related to global warming. I said no, in part because I didn’t really feel qualified to do so, but also because I don’t want to be held liable for making an incorrect prediction. It seems ridiculous, but it’s true.

I didn’t sign on to be a scientist to be held accountable for predicting earthquakes or hurricanes. I signed on so I could learn more about our world – with the hope that what I learn might just benefit others in unexpected ways. I’m certain that’s how those geoscientists in Italy felt as well. They were just doing their job to the best of their ability with the resources and data they were provided.

I think this whole episode has given many scientists pause to think about what they should or should not say publicly. I know I’m not alone.

Beware of Movies! The Interior of the Earth

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 structure and composition of the Earth.

One might think that we have no way to know what the interior of the Earth is like. The Earth is over 6000 kilometers in diameter, and we’re doing good to drill a few kilometers into the crust.

Here’s the reality of the Earth’s structure. At first pass, the Earth is composed of the crust, the mantle, and the core. The mantle and the core are each divided into two parts, the upper and lower mantle, and the inner and outer core.

Structure of the Earth

The crust is the part that we live on. It is very, very thin compared to the rest of the Earth, going down only to about 7 to 70 km (depending on where you are). The base of the crust is marked by the Moho (which is short for the Mohorovičić discontinuity). Below that is the upper mantle down to a depth of about 660 km, followed by the lower mantle down to about 2900 km. It is a common misconception that the mantle, being very hot and under pressure, is molten. This is absolutely untrue. The mantle is solid rock, with one tiny exception in the upper mantle that we’ll get to in a moment.

Below the mantle is the core. The outer core, from 2900 to 5155 km in depth, is the only part of the interior of the Earth that is fully molten. It is composed of molten iron and nickel. It is here where the Earth’s magnetic field is generated. This is one of the few things that were correctly attributed in the movie “The Core.” From 5155 km to the true center of the Earth is the solid inner core, which is composed mostly of iron and nickel.

This simplistic, three-part division (crust, mantle, core) is the extent of the description of the interior of the Earth provided by the movie, “The Core.” Equally, “Journey to the Center of the Earth” (2008) is no better. Both are over-simplifications.

 

Before we move forward, it is probably worthwhile to explore how we can possibly know this much about the interior of our planet. As I already pointed out, we haven’t actually drilled completely through the crust. How can we possibly know the structure or the composition of the interior of the Earth.

The movie “The Core” actually begins to show us how this is done. Solid rock can transmit seismic waves. Every time there is an earthquake somewhere on Earth, it sets off waves that pass completely through the Earth and can be recorded at seismic stations throughout the globe. Some waves pass through the Earth, others can only move along the surface. Seismic stations record both types and seismologists can determine when and where the earthquakes happened based upon when the waves are recorded.

The way that waves pass through the Earth are affected by the types of rock. Some rocks speed up the waves, others slow them down. Waves bounce around inside the earth, too. So a seismic wave might bounce off of the core-mantle boundary. These properties, combined with multiple seismic stations, make it possible for us to know the composition of the Earth and the approximate position of any important boundaries within the Earth.

Furthermore, one type of seismic wave, shear waves, won’t pass through liquids. So if a seismograph recording an earthquake shows no shear waves, we know that the seismic waves went through a liquid. This is how we know that the mantle is solid rock and that the outer core is molten.

Beware of movies: In “The Core,” the terranauts find huge open cavities in the mantle. If such open spaces existed, they would have been evident from seismic studies. No seismic wave could pass through an empty space like that, and we would know about them. Similarly, in “Journey to the Center of the Earth” (2008), the main character discusses the existence of tubes that bypass the mantle and go straight to the core, which in the movie is hollow. Again, seismic waves would have shown such tubes and caverns.

Since earthquakes occur all around the Earth all the time, one needs only to have a global set of seismic monitoring stations, and we can learn all about the Earth’s structure. Such a global network exists. Because of that, we know that the Earth is actually far more complex than just crust, mantle, and core.

 

Many people are aware of the important concept in geology called “Plate Tectonics.” At a first pass, Plate Tectonics explains why it seems like South America and Africa would fit so well together, like puzzle pieces. That’s because they did once fit together and have since moved apart. The moving units on the Earth’s surface are called ‘plates.’ There’s a South American plate and an African plate. They were once together and have since moved apart.

Individual plates are not just pieces of crust moving around on top of the mantle (a common misconception). The plates are pieces of the “lithosphere,” which includes the crust plus the uppermost part of the mantle down to about 100 km. Crust plus the uppermost mantle (called the lithospheric mantle) equals the lithosphere. The crust and lithospheric mantle move as one big piece called a plate.

The structure of the Earth, including the lithosphere.

Below the lithosphere, is the asthenosphere, which goes down to about 400 km in depth – basically much of the rest of the upper mantle. It’s in the asthenosphere that flow occurs.

But wait! The mantle is solid rock! How can it flow?

Two things happen: 1) Just like wax is a solid that can flow, so can the mantle. Individual atoms within the minerals of the mantle can move causing very, very slow flow. 2) Because of temperature and pressure gradients, between 100 and 200 km in depth there is the tiniest bit of melting. The whole rock doesn’t melt, just a few of the minerals. This slows down shear waves, but doesn’t stop them completely, which is how we know this slight melting exists. We call it the low velocity zone, because it slows down the shear waves.

 

The various layers of the Earth have fairly specific compositions. The core is mostly nickel and iron, as previously mentioned. The rest of the Earth’s composition can be explained using Bowen’s reaction series. Read more about it here.

Bowen’s Reaction Series

The basic rocks of the universe are ultramafic rocks, so we would expect that the bulk of the Earth is composed of ultramafic rocks, which are primarily the mineral olivine. Ultramafic rocks are characterized by having high iron and magnesium and low silica.

The crust of the Earth has some mafic rocks and minerals, but most are intermediate to felsic in composition, meaning that there’s high silica, potassium, aluminum, and sodium. These compositions are attained when the mafic rocks of the mantle are melted and erupted, then cycled through the rock cycle multiple times. Every time a rock is re-melted, the most mafic parts of it tend to be last to melt, and might not erupt, resulting in rocks that become more and more felsic over geologic time.

Beware of movies: In “The Core,” the terranauts discover huge amethyst crystals in the upper mantle. Amethyst is a type of quartz, which is a felsic mineral. The mantle is ultramafic. What this means is that quartz would not be stable, it could not exist, in the mantle. This is a big mistake.

Beware of movies: Both “The Core” and “Journey to the Center of the Earth” make the mistake of thinking that diamonds would be abundant in the mantle. The reality is that there are diamonds in the upper mantle, where conditions of temperature and pressure are suitable to form diamonds. And, “Journey to the Center of the Earth” never really specifies where they are in the mantle – probably fairly high, so maybe that’s ok (although there’s an additional problem with muscovite in that movie). In “The Core,” however, they discover huge diamonds presumably in the lower mantle, at least fairly close to the core-mantle boundary. Conditions aren’t suitable for diamonds low in the mantle, lack of carbon notwithstanding. The giant diamonds are bogus.

 

This is the general understanding of the interior of the Earth, and how we know what we know. On this topic, movies are typically either pretty-darn-good or completely wrong. As always, extreme caution needs to be used when trying to apply the science of movies to real life.

*****Added January 15, 2013*****

I’ve discovered that I left some things out of this post. Please visit this post to learn more about what meteorites and magnetism have to do with our understanding of the Earth’s interior.

My dream job?

National Blog Posting Month – December 2012 – Work

Prompt – If you could have any job in the world, what would it be?

—

Any job in the world, eh? Well, I like what I do, so I suspect that wouldn’t change much. I might adjust the hours I worked; five hours a day suits me better than eight. Then again, I pretty-much do that now. I mean, I’m usually in my office for at least five hours a day. After that, if I can, I might just book out of there. That isn’t to say that I don’t make up that ‘missed’ time elsewhere.

I would like to make writing a greater component of my actual job. By that, I mean non-technical writing. I wish working on my novel(s) didn’t have to come out of my sleep. I wish I actually got paid to do that. Or even got paid for the non-technical science blog posts I write. To have that count as ‘work’ toward my paycheck would be delightful.

Truth is though, I think I do have as close to my dream job as I can muster. I have visions of one day writing a block-buster screenplay or novel and becoming a billionaire. I think if that happened I would still do what I do. Less teaching, less lab management for sure, but more science, and waaay more writing.

For 12-11-12

Bad Geology Movies: The Core, 2003

The Core

2003

Aaron Eckhart, Hilary Swank

Premise: What if the Earth’s liquid outer core stopped spinning, resulting in total catastrophe? Can it be set spinning again?

One thing this movie got right: the Earth’s magnetic field is generated in the liquid outer core. The rest, well—

I enjoyed the opening scene with the main character giving a geology lecture about using seismic waves to understand the interior of the Earth. I’ve given that very lecture. I’m just glad my students aren’t so lethargic. It’s pretty amazing actually, since my classroom is considerably darker. I do have one student who’s often working on his nails, but that’s ok. He plays classical guitar.

Moving on to the geological problems with this movie, and there are many…

1) The whole movie oversimplifies the structure of the Earth, dividing it only into crust, mantle, and inner and outer core. It’s substantially more complex than that. The mantle is divided into two parts (upper and lower), and the movie fails to distinguish between the lithosphere (crust and uppermost mantle) and asthenosphere (part of upper mantle). That’s fine though, I guess. If they keep it simple, they can’t be wrong.

The structure of the Earth

2) As our intrepid terranauts are drilling toward the core and about to pass from the crust to the mantle, one of the ground crew comments that passing through the crust is different than the mantle as “the crust is just rock.” Last I checked, the whole planet was ‘just rock,’ with the only possible exception of the liquid outer core.

3) Our explorers find great empty spaces in the mantle, filled with amethyst crystals. Two problems here: a) Any empty spaces would have been most likely recognized by the behavior of seismic waves through the mantle. Shear waves won’t pass through liquids and NO waves would pass through an empty void. There are no empty spaces in the mantle. B) These (impossible) empty cavities are filled with huge amethyst crystals in the movie. Amethyst is a variety of quartz. If one takes a moment to look at Bowen’s reaction series, one would find that quartz is common in felsic rocks, like continental crust. The mantle is ultramafic rock. There isn’t enough silica to make quartz. Quartz would not be stable there. Quartz does not exist in the mantle. But, to give credit where credit is due, at least they got the shape of the crystals right!

4) Somewhere low in the lower mantle, our terracraft bumps into (literally) a bunch of enormous diamonds. I can see the movie-maker’s thinking here: Diamonds form under intense pressure, thus there must be huge diamonds near the Earth’s core. One problem though. Diamonds are composed entirely of carbon. There just isn’t enough carbon in the mantle to make diamonds. At all. Certainly not the gigantic ones portrayed in the movie. That point aside, I have no idea on what basis the identification as ‘diamond’ is made. They certainly don’t have the proper octahedral shape of diamonds. I guess because they show up as black and are thus impenetrable, then they can only be diamonds.

5) They set off the nukes and achieve “full rotation” of the liquid outer core (whatever that means). As I understand the flow of the outer core, it’s not quite as simple as shown in the movie. We call the flow of the liquid outer core, and how it generates the Earth’s magnetic field, the magnetic geodynamo. This link will take you to several other pages that will explain better how this works.

6) The final facepalm of the movie was when the terracraft finds itself launched out from the core and back to the sea floor through a “space between tectonic plates near Hawaii.” Hawaii is smack-dab in the middle of the Pacific Plate. There are no plate boundaries there. Now it is a hot spot, and the crust might be thin, affording an easy exit for our terranauts, but there is no plate boundary.

So these are the major geologic problems with the movie “The Core,” or at least the ones I spotted in the feverish state I was in while watching the film. Read my review of “Journey to the Center of the Earth,” for a completely different yet equally incorrect perspective on what Earth’s interior might be like.

Be careful should you start to think that what’s portrayed in movies has any basis in reality (at least as is understood by science).

Why buying used books is wonderful!

This last weekend, Writers & Books, a local bookstore and writer-gathering hotspot had its “Book Thieves Holiday Book Sale.” My husband picked out a bunch of cool books, including an older astronomy book. This is one of many little notes found inside:

A note stuck into an astronomy book. It reads:
“Comet West – March 5, 1976
5:32 A.M.
There appeared at the top of the window a very brilliant light and in the instant that it took me to focus, right before me was a brilliantly glowing ball but of a hazy shape. greenish in color and indescribably bright. It seemed to wobble a little which must have been its revolutions and moved with a slightly downward curve then was suddenly gone. Sky was overcast for next few days.”

This was fascinating. Who knows where this viewer was when he observed this (though I suppose we could figure it out from the other notes and newspaper clippings tucked into the book).

This does seem as if it would be an interesting opening scene for a book such as mine (The Masters).

Bad Geology Movies: Armageddon, 1998

Armageddon

1998

Bruce Willis, Ben Afflek, Liv Tyler

Premise: What if a Texas-sized asteroid were careening toward Earth and we only had 18 days to stop it?

The idea is an interesting one. We know that there was an asteroid impact on Earth at the same time the dinosaurs went extinct and there is a lot of evidence to suggest that the impact itself was a huge factor causing the extinction. So, what if it were about to happen again, only now we were able to detect the oncoming asteroid and could (potentially) do something about it?

In the opening sequence, the narrator describes the dinosaur-killing asteroid as six-miles wide. That may be right. It seems reasonable, anyway. The narrator goes on to describe a global dust cloud which lasted for 1000 years, through which the sun could not penetrate. For the sake of the movie, that’s as good as anything. But do be aware that there are plenty of competing hypotheses about what happened after the impact. Some involve incinerating the Earth, not coving it with dust. Or triggering volcanoes. Or all of the above. But, that there was an impact is no longer debated.

Since this is about bad geology movies, I won’t go into the details of problems with the rest of the movie aside from the geology. The movie was fairly fun… until they were on the asteroid. Then I started having problems.

1) Our characters miss their landing site by 26 miles. They wind up in a region of “compressed iron ferrite.” They also describe it as a compressed iron plate. Iron ferrite is not any mineral or rock that I’ve heard of. “Ferrite” as a word on its own, is another word that means ‘iron.’ So iron ferrite is an iron-bearing iron rock (or mineral, they never clarify). So it’s redundant. You see the phrase “Iron Ferrite” on google, but I suspect people put the two together because most folks don’t realize that the ‘ferrite’ part already says ‘iron.’

2) All over the place (on the asteroid) are huge crystals jutting all around. It’s reminiscent of Superman’s home planet of Krypton, or perhaps his Fortress of Solitude up in the Arctic. Such crystals aren’t going to form in the vacuum of space, especially not in an area composed entirely of iron ferrite. They looked like gypsum crystals, which wouldn’t make much sense on an asteroid.

3) The topography of the asteroid was bizarre. One would expect craters, with steep slopes and whatnot, but not a “Grand Canyon.” A canyon like that is an erosional feature, that you wouldn’t expect on an asteroid. But maybe it was a great big crack in the asteroid. Why then did they not drill there, where the rock was already fractured and weak?

4) One more thing bothered me, but maybe it’s not so bad. This asteroid seemed to have an atmosphere. There were the random fireballs which made no sense to me. And then the wind blew, slightly, at the end when Bruce Willis’ character picks up some of the dust and let it fall from his hand.

There was just a lot wrong with the asteroid, which spoiled the movie for me, mostly. The movie was enjoyable otherwise, with some fun and charming characters.

Beware of Movies! Foundations of Geology – Minerals and Rocks

Beware of Movies! will be a series of blog posts discussing important concepts in geology while making reference to scientific errors in movies and TV regarding geological concepts. These posts go in concert with a lecture series I’m preparing with the same idea. It seemed fun.

This is the first post in the Beware of Movies! series.

A common misconception about geology is that it is a science ONLY about minerals and rocks. Well, and oil. But that’s it. Geology is a tiny bit more complex than that. However, it does include rocks (and minerals) as an important fundamental basis. A person can’t say much in any field of the earth sciences without first knowing quite a bit about minerals.

MINERAL:

1) Naturally occurring

2) Inorganic

3) Solid

4) Specific crystalline structure

5) Specific chemical composition

Any compound that fits the above definition is a mineral. Ice (frozen water) is a mineral because it satisfies these criteria.  Bismuth hopper crystals do not satisfy these criteria because they’re synthetics, so, while quite lovely, they do not constitute a mineral.

CHEMISTRY:

When I start to talk about chemistry, my Introductory Geology students always groan. But I’m always able to assure them that what matters here is pretty basic and that it’ll be over soon. Chemistry matters because minerals have a specific chemical composition. This means that the individual atoms that go into a mineral are specified. The atoms are specific elements, like carbon and oxygen, and certain numbers of each of them combine (bond) to form the minerals. I will spare you the details of how the atoms bond. What’s important is that atoms have size. They’re like little spheres of differing sizes depending on the elements. When you try to stack the elements together, they stack in very specific ways. That is what causes the crystalline structure of minerals.

The stacking of the elements forming a mineral also results in all the recognizable properties of minerals that we use to identify them, including:

Color – what color is it?

Luster – how would we describe the shininess of the mineral? Metallic, earthy, glassy.

Specific gravity – how dense is it?

Crystal form – what shape are the crystals?

Cleavage and fracture – how do the crystals break? Do they break along specific planes or along random surfaces?

Hardness – is the mineral soft, like talcum powder, or hard like diamonds?

MINERAL GROUPS:

Minerals are grouped by their basic chemistry:

Oxides – have oxygen (O) like Fe2O3, hematite (rust).

Sulfides – have sulfur (S) like PbS, galena.

Sulfates – have sulfate (SO4) like CaSO4 H2O, gypsum.

Carbonates – have carbonate (CO3) like CaCO3, calcite (chalk).

Native elements – gold, silver, carbon like diamonds!

Silicates – have silica (The silica tetrahedron – SiO4) like SiO2, quartz

Beware of movies: In Armageddon (1998), our heroes are forced to drill into an asteroid to implant a nuclear device. Where they wind up setting down, so claim the characters, is composed of “iron ferrite.” That’s not any mineral I’ve heard of. It’s a redundant name, actually, because the ‘ferrite’ part, like ‘ferric’ or ‘ferrous,’ refers to iron. So iron ferrite is an iron-bearing iron rock.

SILICATES:

This is the most important group of minerals on Earth, in that they constitute most of the Earth. Therefore, oxygen and silicon are the most abundant elements on Earth. Life is carbon-based, but we’re just a think veneer on a very, very large sphere. But if silicon is so common, why are there not silicon-based life forms?

Silicate minerals are categorized by how the silica tetrahedra relate to each other in the mineral. They can be isolated, or bonded to one another by sharing the one or all of the oxygens on the tips of the tetrahedra, to form chains, sheets, or complex networks. While this sounds like there’d be lots of silicate minerals, it turns out that there are relatively few that a person needs to know to be able to identify most minerals in ordinary rocks. We’ll get to that in a moment.

ROCK:

A rock is an amalgamation of individual mineral grains. Often there are several minerals in a rock, like granite that contains quartz, biotite, and two types of feldspars. But a rock can be composed of grains of all one mineral. The best example of this is a nice clean sandstone which can be made of only quartz grains.

Beware of movies: In Journey to the Center of the Earth (2008), Muscovite is called a “thin rock formation.” Muscovite is a mineral, not a rock. It does make nice thin sheets (because of its cleavage), but it’s not a rock.

BOWEN’S REACTION SERIES:

Bowen’s reaction series describes the stability of silicate minerals under different temperature regimes. Minerals at the top of the reaction series, form under conditions of extreme heat, but are not stable at the lower temperatures at the Earth’s surface. Minerals at the bottom of the series are more stable at low temperatures (like those on the Earth’s surface).

Understanding Bowen’s reaction series will help anyone identify minerals in a rock. See, the minerals that go together in a rock aren’t just randomly selected. Certain minerals occur together. Some minerals are never found together in a rock. The minerals that can occur together are those that are stable at the same temperature ranges. So Olivine and Quartz will never occur in the same rock, for example.

The minerals that are stable at high temperature are the mafic minerals, which are high in magnesium, iron,and calcium, and low in silica. The minerals that are stable at low temperatures (and are common on the Earth’s surface) are called felsic minerals, and are high in silica and hight in sodium, potassium, and aluminum. This doesn’t matter now, but will matter later when we think about volcanoes.

Beware of Movies: The movie “The Core” seemed to struggle a bit with Bowen’s reaction series. The mantle of the Earth (the layer below the crust, where we’re living), is composed of ultramafic rocks. This means, high iron, high magnesium, and low silica. However, in the movie, the intrepid ‘terranauts’ find themselves in a large empty cavity in the upper mantle that is full of amethyst (quartz) crystals. Quartz is felsic. It would never be stable in the mantle. This is a massive mistake.

ROCK GROUPS:

All rocks on Earth can be divided into three groups (and some might fit into more than one).

Igneous rocks: Those rocks that formed from the cooling of molten rock (magma). In these the crystals that make up the rock form according to Bowen’s reaction series (as well as the composition of the magma itself).

Sedimentary rocks: Rocks that formed from the deposition of bits and pieces of other rocks that have been broken down and (probably) transported elsewhere. Alternatively, sedimentary rocks can form from the precipitation of crystals directly out of water, rather like hard water deposits.

Metamorphic rocks: If pre-exisiting rocks of any kind are subjected to great heat and/or pressure, the minerals present, and their relationships to one another may change. This results in metamorphic rocks.

Beware of movies: Bowen’s reaction series helps explain what silicate minerals might go together. There are similar limitations on what other minerals might occur together by what rock type they will be found in. In Journey to the Center of the Earth (2008), they find rubies, emeralds, and diamonds together in a lava tube. None of these would occur together. Emeralds are usually found in felsic igneous rocks. Rubies are found in metamorphic rocks, and diamonds form deep in the mantle, far away from either of the places where emeralds or rubies might form.

ROCK CYCLE:

Any of the three types of rock (igneous, metamorphic, or sedimentary) can be changed into any other type of rock in what is called the rock cycle. Existing rocks can be melted and cool again to make new igneous rocks. Existing rocks can be broken down, transported, and redeposited into sedimentary rocks. And any existing rock can be exposed to high heat and pressure to form a metamorphic rock. The end result is that there are very few tremendously old rocks on Earth, because most have been recycled.

These are some of the basic concepts necessary to understand further topics in geology. Without this basis, it would be impossible to begin to interpret the Earth’s history from its rock record.

Bad Geology Movies: Journey to the Center of the Earth, 2008

The second in a series of posts about what’s wrong in movies with geology-related themes.

Journey to the Center of the Earth

2008

Brendan Fraser

Premise: What if Jules Verne’s story “The Journey to the Center of the Earth” were real?

First things first: This movie clearly was never meant to be scientifically accurate. Once you accept that, it’s actually a fairly fun movie. But if you go into it expecting good science, you’ll be disappointed. What worries me is that there may be people who actually think that the science portrayed in the movie is valid. That’s a problem.

It’s based loosely on the original book by Jules Verne, which was written when nothing was know about the Earth’s interior. I’ve read the book and struggled momentarily to accept that it is the truest kind of fiction and was written with none of the modern knowledge of the Earth.

I accept that this movie (nor the book) are based upon real science. Most everyone knows that the Earth is not hollow, with a habitable cavern near its core. (Well, most anyway.) In the story, there are hypothesized tubes that go past the mantle and into the center of the Earth (this is how our main characters gain access to the big cavern).

The Structure of the Earth

There is absolutely no evidence that such a thing could exist. The Earth is solid, with no air spaces or bubbles (habitable or not) anywhere. Part of the core is liquid (molten), but other than that, the whole thing is solid.

OK, wise guy, you think. How can you possibly know that?

Much of our understanding of the interior of the Earth comes from the recoding and interpretation of seismic waves that pass through the planet. Every time there’s an earthquake on Earth, seismic stations (seismographs) pick up the vibrations kicked off. These vibrations can be used to determine where and when an earthquake happened, and is how the geologists can pinpoint earthquake epicenters and also the magnitude of the quakes.

But the seismic waves set off by an earthquake provide much more information than that. There are several different types of waves that occur due to earthquakes. Some only move on the Earth’s surface. Others only pass through the body of the Earth. Some cannot pass through liquids. A seismograph picks up all of these. By looking at seismograms from several stations and seeing which waves show up, we have been able to determine the structure of the interior of the Earth.

The liquid outer core stops some waves – so we know it’s liquid. All seismic waves pass through the mantle just fine, so we know there’s no pockets of liquid or air in there.

Sorry folks. No cavern in the center of the Earth.

So, here’s some more nit-picky things to think about:

1) Veins of Magnesium. These show up a few times in the movie. For one, I’ve never heard of veins of magnesium. For two, when they’re in the lava tube, trying to light the magnesium, it should go crazy because of all the water present. That it’s wet should help things, not hinder the burning.

2) To find rubies, emeralds, feldspars, and diamonds all in one place like they do is really unlikely. Finding feldspars with any of those gems is not really that surprising, since feldspars com in all sorts of varieties, but the conditions to form the other gems are all different from one another.

And the shape of the raw diamonds are all wrong. They looked like plastic to me – not like diamonds at all. You see, minerals grow in specific shapes. Diamonds form little octahedrons, which was clearly missed by the movie prop people.

What made this gaffe a little worse was that the main character (a geologist) said that these minerals and gemstones are common in volcanic tubes. Clearly, this is just a line for the movie (although diamonds can be found sometimes where there have been explosive, deep eruptions called kimberlites).

3) Muscovite is a mineral, not a “thin type of rock formation.” Muscovite is a very important rock-forming mineral. It doesn’t tend to form platforms with open chasms below. The comment that changes in pressure can cause muscovite to shatter is also not true. So as a mineral, they’ve got muscovite wrong. As a plot device, it’s pretty interesting.

4) When the main character tells everyone that those cute little bio-luminescent birds have been extinct on the Earth’s surface for 150 million years, I cringed. There were no modern birds 150 million years ago, only some archaic birds and some dinosaurs. Maybe I’ll just give him the benefit of the doubt that he meant 50 million years. That I could accept (though it’s probably still far-fetched!).

5) The discussion of how magnetic polarity is reversed at the core was kind of strange. I would expect that a compass would be useless near the core only because you’re right next to where the magnetic field is being generated, but that a compass should point South instead of North isn’t right.

6) Speaking of magnetism, how about those floating magnetic rocks? If the magnetic field is strong enough to make the rocks float, I would have expected that the kid’s metal gear would also float, and probably the kid as well. This scene just bugged me as being completely impossible, even when I accepted that the movie is purely fiction. I was even ok with the muscovite problem much more than this.

7) Since I am a paleontologist, I do feel obligated to point out that the dinosaur skull that they used as a raft/sled is all wrong. What they’ve done is combined a dinosaur skull (which is full of holes) with a mammal skull (that has fewer holes), left out all the important openings in the bottom of the skull, and called it a raft.

8) Back to the whole magnesium thing. When they’re stuck in the skull and trying to light the magnesium so that it’ll break the walls and release the water on the other side, which would then fall on the magma and make steam and shoot them out of the lava tube. Well, a) would not the heat from the lava have lit the magnesium? b) there’s no way there’s water on the other side a a lava tube just waiting to get out. Besides, c) the water should have made the magnesium ignite better with the lava in the first place. And, d) wait, how is this magnesium even there (or the water) if they’re stuck in a lava tube that’s had lava in it? This one made me facepalm.

Anyway, the movie was an enjoyable romp, provided one realizes from the very beginning that the ‘science’ portrayed is very much fiction. The highlight for this movie was when, 3/4 of the way through, my 8-year-old son turned to me and asked me if it was real. I assured him that it was not. He seemed relieved.

What am I a “pro” at? – Isotopic Analysis of Bioapatites

National Blog Posting Month – December 2012 – Work

Prompt – What do you consider yourself a “pro” at?

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It seems strange to ever consider myself a “pro” at anything. I’m ‘good’ at a lot of things, and feel like I’m pretty well-rounded as a person and a scientist, to say “pro” makes me hesitate.

However, there is one topic (work-related, of course) that about which it appears that I am considered a world expert. I get sufficient requests from entities globally each year to corroborate that conclusion. On that one thing, I will – still reluctantly – call myself a “pro.” That topic is the analysis of light stable isotopes from bioapatites.

In English, this is basically the geochemical analysis of tooth enamel. I work mostly with the teeth of fossil mammals. The data collected from such analyses can be used to interpret ancient environments and habits and dietary preferences of extinct animals. From that, we can study things like climate changes that occurred millions of years ago. That’s my schtick.

There are lots of scientists actually that work with such data. By lots, I mean maybe a few hundred, so still a small number but greater than zero. What makes me unique is that I’m one of the very, very few who actually knows how to operate the instrumentation to do the analyses. It’s one thing to understand how to interpret the data. It’s quite another to know how to get the data. Not only can I run the analyses, I can replicate my results, which is actually much harder than it sounds.

I always giggle a bit when I get an e-mail that says something to the effect of “I’ve heard you’re the best at this, so here’s some samples, can you run them?” My first thought is, Clearly these people haven’t met me. But I get these requests from all over the world, with projects pending and running from Australia, Brazil, Uruguay, and Siberia, not to mention the stuff happening in the United States, so there must be something to it.

So that’s what I’m a “pro” at, I guess. Isotopic analysis of bioapatites. I’ll put that on my resume.

For 12-3-12