Forensic geology

I've been interested in rocks since I was a kid.  My dad was a rockhound -- more specifically, a lapidary, who made jewelry from such semiprecious stones as turquoise, agate, and jasper.  The high point of my year was our annual trip to Arizona and New Mexico, when we split our time between searching for cool rocks in the canyons and hills of the southwestern desert and pawing through the offerings of the hundreds of rock shops found throughout the region.

Besides the simple beauty of the rocks themselves, it fascinated me to find out that with many rocks, you could figure out how and when they formed.  A lot of the gem-quality rocks and minerals my dad was looking for -- malachite, azurite, and opal amongst them -- are created by slow precipitation of layers of minerals from supersaturated water; others, such as lapis lazuli, rhodonite, and garnets form when metal-bearing rocks are metamorphosed by contact with magma far underground.

[Image licensed under the Creative Commons Olga Semiletova, Минералы горных пород, Creative Commons Attribution-Share Alike 4.0 International license]

Once I found out that the "when" part was also often knowable, through such techniques as radioisotope dating and stratigraphy, it was always with a sense of awe that I held pieces of rock in my hand.  Even around where I live now, where there are few if any of the lovely gem-quality stones you find in the southwest, there's still something kind of mind-boggling about knowing the layers of limestone and shale that form the bedrock here in upstate New York were formed in the warm shallows of a warm ocean during the Devonian Period, on the order of four hundred million years ago.

But if you think that's impressive, wait till you hear about the research out of the University of Johannesburg that was published in the journal Icarus last week.

The research centered around a stone in the desert of western Egypt called Hypatia, given the name by Egyptian geologist Aly Barakat in honor of the brilliant, tragic polymath whose career was cut short when she was brutally murdered by a mob on the orders of Cyril, bishop of Alexandria.  (The aftermath, although infuriating, is typical of the time; Hypatia was largely forgotten, while Cyril went on to be canonized as a saint by the Roman Catholic Church.)  The stone, fittingly considering Hypatia's contributions to astronomy, turns out to be extraterrestrial in origin, later falling as a meteorite to the surface of the Earth.

But "extraterrestrial" is a big place, as it were.  Where exactly did it form?  Chemical tests on the rock found that it didn't match the composition of any known asteroid or comet; then, the mystery deepened when it was found to contain nickel phosphide, which has never been found on any solid material tested in the entire Solar System.

Further tests only made the rock seem more anomalous.  Silicon, second only to oxygen as the most common element in the Earth's crust (a little over 28%, to be exact), was almost absent, as were calcium, chromium, and manganese; on the other hand, there was far more iron, sulfur, phosphorus, copper, and vanadium than you'd expect.  The ratios were far off not only from rocks in our Solar System, they didn't match the composition of interstellar dust, either.

The researchers decided to go at it from the other direction.  Instead of trying to find another sample that matched, they looked at what process would create the element ratios that Hypatia has.  And they found only one candidate that matched.

A type 1a supernova.

Type 1a supernovas occur in binary star systems, when one of the stars is relatively low mass (on the order of the Sun) and ends its life as a super-compact white dwarf star.  White dwarf stars have an upper limit on their mass (specifically about 1.4 times the mass of the Sun) called the Chandrasekhar limit, after Nobel Prize winning astronomer Subrahmanyan Chandrasekhar.  The reason is that at the end of a star's life, when the outward pressure caused by the fusion in the core drops to the point that it can't overcome the inward pull of gravity from the star's mass, it begins to collapse until some other force kicks in to oppose it.  In white dwarf stars, this occurs when the mutual repulsion of electrons in the star's constituent atoms counterbalances the pull of gravity.  In stellar remnants more than 1.4 times the mass of the Sun, electrostatic repulsion isn't powerful enough to halt the collapse.  (The other two possibilities, for progressively higher masses, are neutron stars and black holes.)

In binary stars, when one of the members becomes a white dwarf, the gravitational pull of its extremely compact mass begins to siphon material from its companion.  This (obviously) increases the white dwarf's mass.  Once it passes the Chandrasekhar limit, the white dwarf resumes its collapse.  The temperature of the white dwarf skyrockets, and...

... BOOM.

The whole thing blows itself to smithereens.  Fortunately for us, really; a lot of the elements that make up the Solar System were formed in violent events such as the various kinds of supernovas.  But the models of the relatively rare type 1a (only thought to happen once or twice a century in a typical galaxy of a hundred billion stars) generate a distinct set of elements -- and the percent composition of Hypatia matches the prediction perfectly.

So this chunk of rock in the Egyptian desert was created in the cataclysmic self-destruction of a white dwarf star, probably long before the Solar System even formed.  Since then it's been coursing through interstellar space, eventually colliding with our obscure little planet in the outskirts of the Milky Way.

When I was twelve, holding a piece of billion-year-old limestone from the Grand Canyon, little did I realize how much more amazing such origin stories could get.

I think the real Hypatia would have been fascinated.

**************************************

Rock of ages

One of the simplest, but one of the most mind-blowing, concepts in science is that matter is recycled indefinitely.

It came up in a variety of ways in my biology classes, most frequently because of the water cycle, nitrogen cycle, and carbon cycle.  I always told my classes, "Every drop of water in your body has been in many forms.  It's been in clouds, it's been in rain, polar ice, the oceans and lakes.  It's been tree sap, bird blood, and dinosaur piss.  It never is created or destroyed, it just keeps getting reused."

This recycling, however, does make certain things hard to study, because the process of the recycling often erases where those molecules had been before and what they'd been doing.  This is most obvious in geological cycles.  When a geologist says, "This rock is recent, it was formed only a few hundred years ago," or "this is an ancient rock dating back to around eight hundred million years ago," (s)he is not talking about the materials; the materials, for the most part, all ended up on Earth at around the same time.  (Exceptions are meteorites, which will come up again shortly.)  The materials that make up yesterday's cooled lava rock and the rock of the Precambrian-Age Laurentian Shield of Canada are the same age; what's different is when the last event occurred that modified them enough to erase their previous history.

Because those history-erasing processes are happening all the time, this makes it difficult to find rocks that are over a billion years old, because the likelihood of a rock surviving unmelted all that time is virtually nil.  This makes our knowledge of the geological history of the Earth sketchier and sketchier the further back in time we go, and honestly, any models we have about the position of the continents and their relationships to the current configuration pretty quickly devolve into pure speculation much earlier than the Cambrian Period -- meaning that 7/8 of the entire history of the Earth is pretty much uncharted territory, geologically-speaking.

All of this is why it was quite a shock when I found out, from a paper in Proceedings of the National Academy of Sciences this week, that a rock has been found containing grains that date from between five and seven billion years ago, and some may be older than that.

Electron micrographs of presolar grains from the Murchison meteorite [Image by Philipp R. Heck, et al., of the University of Chicago]

If you're saying, "Wait, isn't that older than the Earth?", the answer is "yes."  The Earth's surface cooled and became solid on the order of 4.6 billion years ago.  So how can this possibly be correct?

The grains, it turns out, are part of a space rock called the Murchison meteorite that landed in Australia in 1969, so while everything on Earth was getting melted down, smashed, and mixed around, the rock of the Murchison meteorite was safely out in space, preserving the interior as a sort of time capsule of the very early Solar System.  These "presolar grains" of silicon carbide were dated using known conversion rates of the component atoms to other elements from interacting with cosmic rays, in some cases giving ages that are about as old as the Sun itself.

As far as how this can be, it bears keeping in mind that the Sun itself is thought to be a "third-generation star," so therefore nowhere near as old as the Universe as a whole.  The earliest stars were composed solely of hydrogen (and helium, as the hydrogen fuel was consumed), and heavier elements formed in the death throes of those stars.  The heaviest elements all were formed in supernovas, so any star enriched in these elements -- as our Sun is -- must contain materials from at least one, probably more, previous generations of stars.

So these silicon carbide grains were formed from atoms generated in stellar furnaces that predated the Sun (thus their name, "presolar grains"), and were floating around in interstellar space for all that time until a chunk of them happened to discover that Australia was in the way.  Fortunately for us; it gives us a chance to see materials about as old as you could find anywhere -- dating back to a time when the Solar System was still a ring of coalescing debris around a very young star.

*****************************

This week's Skeptophilia book of the week is scarily appropriate reading material in today's political climate: Robert Bartholomew and Peter Hassall's wonderful A Colorful History of Popular Delusions.  In this brilliant and engaging book, the authors take a look at the phenomenon of crowd behavior, and how it has led to some of the most irrational behaviors humans are prone to -- fads, mobs, cults, crazes, manias, urban legends, and riots.

Sometimes amusing, sometimes shocking, this book looks at how our evolutionary background as a tribal animal has made us prone all too often to getting caught up in groupthink, where we leave behind logic and reason for the scary territory of making decisions based purely on emotion.  It's unsettling reading, but if you want to understand why humans all too often behave in ways that make the rational ones amongst us want to do repeated headdesks, this book should be on your list.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!] 

Rock falls and sea levels

Why do we tolerate abject stupidity in our leaders?

I'm asking this not, surprisingly, because of Donald Trump, but because of Representative Mo Brooks of Alabama, a member of the House Committee on Space, Science, and Technology,who claims -- and I am not making this up -- that sea level rise is not being caused by climate change, but by rocks falling into the ocean.

At the time of this writing, I have been emailed this story five times by loyal readers of Skeptophilia, usually accompanied by the words, "What the fuck is wrong with these people?"  In case you are disinclined to believe that someone can be that big an idiot, here's the actual quote:

What about the White Cliffs of Dover … [and] California, where you have the waves crashing against the shorelines, and time and time again you have the cliffs crashing into the sea?  All of that displaces water which forces it to rise, does it not?  Every single year that we’re on Earth, you have huge tons of silt deposited by the Mississippi River, by the Amazon River, by the Nile, by every major river system — and for that matter, creek, all the way down to the smallest systems.  Every time you have that soil or rock or whatever it is that is deposited into the seas, that forces the sea levels to rise, because now you have less space in those oceans, because the bottom is moving up. You put it all together, erosion is the primary cause of sea level rise in the history of our planet and these people who say to the contrary may know something about climate but they don't know squat about geology... 

Keep in mind I'm talking millions, tens of millions, hundreds of millions of years, erosion is the primary cause of thousands, if not tens of thousands, of cubic miles of sea displacement that in turn forces the sea levels to rise.

It didn't take long for a story to appear in the Washington Post estimating the size of the blob of rock you'd have to drop into the ocean to see what we're seeing (a 3.3 millimeter rise per year).  The answer: 1.19 trillion cubic meters, equivalent to a sphere eight miles in diameter.

Every year.

Put another way, this would be like scraping the top five inches of dirt from the entire United States, rolling it into a ball, and dropping it into the ocean.

Every year.  In case I haven't made that point clear.

[Image licensed under the Creative Commons Immanuel Giel, White Cliffs of Dover 02, CC BY-SA 3.0]

Brooks went on to say that the polar pack ice is actually increasing, and the tired old story about how climatologists in the 1980s said there'd be "global cooling," and that didn't happen:

What I'm trying to establish is that a lot of these climatologists have no idea what they're really talking about, and it's because we have not had a long enough period time with exact scientific measurement to know what the climate's going to be like fifty years from now or a hundred years from now.   The bottom line is nobody is smart enough to know with the evidence we have and the relatively small time frame we have - fifty years in the history of the planet.  That's just not enough information with which to make accurate predictions.

Of course, we do have more information than that; we have accurate proxy records going back thousands of years, and some pretty shrewd guesses going back millions.  The link between carbon dioxide and global temperature, and predictions of what would happen if we kept burning all the fossil fuels we could get our hands on, go all the way back to Svante Arrhenius in 1896.  At least Brooks has a clear understanding of how someone could be this willfully stupid, ignoring mountains of evidence and the arguments of climatologists (i.e., the people who actually understand what's going on, despite Brooks's pronouncement that they "have no idea what they're really talking about"):

Money.  Money to invest in a certain kind of resources where you might have a financial interest.  There's also politics as you're trying to cobble together the votes to win an election, that's probably part of it, too.

Which is spot-on, even if not in the way he meant it.  The ones getting rich are not the climatologists -- it's not like you routinely see climatologists living in mansions and driving Jaguars.  The ones who are getting rich are the politicians, who are being bankrolled by the fossil fuel interests, to the tune of millions of dollars annually.

Which, presumably, is how imbeciles like Mo Brooks "cobble together the votes to win an election."

The cure, of course, is an educated electorate, but with the disinformation campaign going on right now, there's been so much distrust of the experts sown in the minds of laypeople that you can tell them damn near anything you want.  The first thing that the talking heads and corporate lobbyists do is to teach people to doubt the facts -- to claim that the data itself is wrong, skewed, or deliberately falsified.  The Earth's not warming, the sea's not rising, storms are not getting stronger.  Oh, and even if the Earth is warming up, all that's going to do is make the cold parts of the world nice and balmy.

Don't worry.  We're not doing anything dangerous.  Trust us.

At least one person was willing to call Brooks on his bullshit, and that was Philip Duffy, president of the Woods Hole Research Center in Massachusetts, who amazingly was asked to participate in the meeting of the House Committee on Space, Science, and Technology, despite being an actual scientist.  He and Brooks had the following testy exchange:

Duffy: We have satellite records clearly documenting a shrinkage of the Antarctic ice sheet and an acceleration of that shrinkage. 

Brooks: I'm sorry, but I don't know where you're getting your information, but the data I have seen suggests — "  

Duffy: The National Snow and Ice Data Center and the National Aeronautics and Space Administration. 

Brooks: Well, I've got a NASA base in my district, and apparently, they're telling you one thing and me a different thing.  But there are plenty of studies that have come that show with respect to Antarctica that the total ice sheet, particularly that above land, is increasing, not decreasing.

In other words, your NASA is clearly wrong.  There are "plenty of studies" showing that my NASA is right.

The whole thing is profoundly upsetting, at least to those of us who know how to read a scientific paper.

On the other hand, at least we don't have to fret about what will happen if the White Cliffs of Dover collapse.  It'll be upsetting to the people in that part of England, no doubt, but there's no worries about the resultant sea level rise flooding Omaha or anything.

***********************

This week's recommended book is an obscure little tome that I first ran into in college.  It's about a scientific hoax -- some chemists who claimed to have discovered what they called "polywater," a polymerized form of water that was highly viscous and stayed liquid from -70 F to 500 F or above.  The book is a fascinating, and often funny, account of an incident that combines confirmation bias with wishful thinking with willful misrepresentation of the evidence.  Anyone who's interested in the history of science or simply in how easy it is to fool the overeager -- you should put Polywater by Felix Franks on your reading list.