Rock Ages and Distance from Volcanoes

Sometimes questions come in that start off all “rong” – It then becomes necessary for us to set the record straight. Sincere efforts, however, should not go unrewarded. The following question is an example.

Q: My name is Mike W.  I'm a HS science teacher from Sibley, Iowa.  I'm really trying to change my labs and activities so they're more realistic and I have an idea.

I've attached an image of the graph I want the kids to eventually make (image showed  a fake graph with dots lining up along a diagonal line, one axis being distance and the other age attached), where they plot age of igneous rock v. distance from active volcano.  Obviously, it's a generally linear graph, which is great b/c they then can get an equation.  But, I want to do more than just give them a data table.  

I was thinking...

Could I give them rock "samples" (15-20) and each rock sample that they get has an identification number and distance from volcano.  In addition, each "sample" would have a visual representation of the remaining radioactive/non-radioactive isotopes left....getting them to use radiometric decay to date their rock sample.  For instance, sample B would be 2.5 km from the volcano and it would have 5 blue circles (parent) and 35 green circles (daughter).  They could deduce that three half lives have passed and the rock is x number of millions of years old.

I want this to be accurate, yet doable in the classroom.  Do you have any thoughts or suggestions???

Thanks so much!!! 

--Mike W

A: Ummmm. I think you have started from a false premise - that rocks are older the farther away they are from a volcano. I can think of many exceptions to this "rule" -- in fact so many exceptions that it cannot possibly be true.

However, I certainly understand and support your hope to get your students actively involved. Real-world, really cool examples are what drew me from a physics PhD track to geosciences. 

I hope soon to have a publication on the web that your students might be able to make use of. It concerns magnetic and gravity and radiometric data acquired around Newberry Volcano in Oregon (Newberry's footprint is at least 20 times larger than Mount St Helens). If you look at the potassium-40 image, you can see that the youngest eruption (~1,300 YBP) blew tephra out eastward at least 100 km: there is a bright red trail extending from Paulina Peak to the east. Careful sampling has shown that it thins the farther east you go. The problem: there are older tephra underlying this blast that didn't reach as far away. 

Volcanoes are generally messy creatures - many of them may look like neat stratocones, but when you unravel their history with careful mapping, you find that they have very complex histories, and the symmetric cone represents just the latest eruptive episode with the first stage of erosion still well underway. Dating volcanic flows and tephra layers is very difficult - when I served a 5-year tour as chief scientist for volcano hazards, I poured must of the extra funding I could lay hands on into telemetry bottlenecks and a dating laboratory. When you want to know how dangerous a volcano is, you need to see how many times - and how violently - it has erupted over time. It turns out that radioelement dating is extraordinarily complex. First, you have different half-lives that limit their applicability: C14, argon-argon, rubidium-strontium, potassium-argon, uranium-lead, etc. Then you have different availabilities - there is almost no potassium or uranium in mafic and ultramafic rocks, for instance. You must painstakingly look and hope for sphene crystals to do any argon dating. THEN you have the contamination issue: when you are doing argon-argon dating, you have to deal with the fact that the air has more argon in it than the grains you are trying to date. The statistics involved are mind-boggling, but it turns out that where you sample is the most critical part affecting success. 

Where you CAN get a good age-vs-distance curve is with an ocean-floor spreading center. The symmetric magnetic banding across the Mid-Atlantic Ridge is a case in point. Deep-sea drilling has sampled the different magnetic-polarity bands and has verified that the farther you move away from the spreading center the (a) older the rocks are, and (b) the deeper the rocks are. You can get a VERY clear age-vs-distance pattern there, because this is a relatively steady-state, on-going process. 

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Is this a Meteorite?

At Ask-a-Geologist, we see a disproportionate number of “What’s this rock” questions. Often they are accompanied by a blurry photo, and we find ourselves trying to explain the sometimes complicated path we must follow to identify a rock ourselves. The following query is a bit different – and not just because it had no photo attached. I hope the answer will help encourage readers to remake themselves into amateur scientists. The fact that the question was asked in the first place is encouraging to me - because no questions asked means nothing learned.

As an aside, several fields of science have discovered that they can make a huge progress by engaging interested amateurs in their research programs. Classifying galaxies, folding proteins, and tracking bird species are just some of these. Some of the greatest science of the 19th and 20th Centuries was done by amateur scientists; Einstein was a patent clerk when he published Special Relativity in 1905.

 

Q: I have a rock. I think it's a meteorite. Where can I take it to have it tested? I am in San Bernardino, CA.

Thank you,

Nancy B.

A: Some background first, so you can better understand what you might have in your hand.

Meteorites are not commonly found lying on the ground. They are found disproportionately in the Antarctic and in snow-covered areas. As you might instinctively expect, they fall in equal numbers everywhere on the planet. However, in Antarctica they impact ice and snow, and do not get mixed in and confused with Earth rocks. The ice and snow in Antarctica become glaciers, carrying their meteorite collections along like a conveyor belt. The glaciers tend to sublimate (evaporate) near their lead edges - where the meteorites accumulate. Consequently, dark rocks falling out of white ice are concentrated, easy to see, and have not been mixed in with Earth rocks. For slightly different reasons (among other things, there is no conveyor belt concentrating mechanism), the Sahara and the Empty Quarter of Saudi Arabia are also places where meteorites are more readily found – they stand out sharply in the white-to-beige sand dunes and flat lag-gravel plains.

Almost all meteorites break up in the upper to middle atmosphere of the Earth, and the fragments that don't burn up generally fall to the ground at their terminal velocities in air. This is typically greater than 200 km/hour on average, and they have punched through cars and houses in the past. Some exceptions to the atmospheric breakup rule include the nickel-iron asteroid fragments, which can easily make it through the Earth’s powerfully protective atmospheric blanket. With the Wabar object that I once mapped in the Empty Quarter of Saudi Arabia, we calculated the mass (from crater diameters) to be about 3,500 tons at impact. Compositionally, it was fairly uniformly 94% iron, 5% nickel, and the rest was cobalt, copper, and iridium (a so-called “sidereal” element not normally found on the Earth’s surface). “Irons” represents only about 2% of the stuff floating around in the Asteroid Belt (most of which are stony or chondrite objects). However, iron meteorites represents about 5% of the meteorites found on Earth. Why the higher percentage? Because blackened metal is far more easily identified when picked up than an ablated (burned-looking) rock that falls among other similar-looking Earth rocks.

Meteorites are notoriously difficult to identify - in large part because there are sooooo many rocks that could easily be mistaken for a meteorite. As a rough approximation, probably less than 1 object in 10,000 that people THINK could be a meteorite actually turns out to BE a meteorite. Moreover, most professional geologists don't know how to distinguish a meteorite from a look-alike... This is because most geologists have never seen a meteorite (they are rare), except for a few under-representative examples in a museum somewhere. In other words, they have never been able to handle and examine a meteorite like the rocks they examine in the field areas where they are commonly working. To put things in perspective, there are far more gemologists than real meteorite specialists in the world.

I wish I could help you myself, but I do not consider myself a meteorite specialist. Moreover, the US Geological Survey is not funded by Congress to study meteorites - we have very specific tasks that we are assigned to do, such as monitor volcanoes or carry out mineral resource assessments (like me). Consequently, any studies outside of these assigned tasks we must do on our own time - because we find the subject interesting.

In my case, for instance, I was drawn into the meteorite field almost accidentally when I visited and mapped the Wabar meteorite impact site a number of years ago. Accompanying me on one of our three trips was one of the foremost meteorite impact specialists in the world at the time, Gene Shoemaker (the “Father of Astrogeology”), and he provided a massive data-dump of his experience for me. Many of the few "real" meteorite specialists that I have personally known in or outside the US Geological Survey are now either dead (Gene tragically died in a vehicle accident in Australia) or retired. One transferred to NASA, because he couldn't do what he wanted most to do (study meteorites) in the USGS. There are meteorite specialists in the Smithsonian in Washington, DC, but both NASA headquarters and the Smithsonian are on the opposite sides of the continent from you. There are a few meteorite specialists at the Lunar and Planetary Lab at the University of Arizona in Tucson, and there are individuals who are competent to assess meteorites in the Astrogeology science center of the US Geological Survey in Flagstaff, Arizona, among others.

All THAT said, how DO you identify the sample you have? I will offer you two lines of approach, but both require that you expend significant efforts to learn more. In essence, both require you to teach yourself to become an amateur meteorite scientist:

1.      Easier Path: Search the internet for books on, and photo examples of, meteorites. Look closely at any that show texture (for instance tectites have a distinctive texture but are not technically meteorites). Keep in mind that there are quite a number of different types of meteorites, from Stony to Chondrite to Nickel-Iron, to rare Pallasites and Nakhlites, as well as others. This list, by the way, is in increasing order of how rare they are. First become familiar with the possibilities, then when you see one that looks like your sample, search for other examples of that type. ESPECIALLY search for detailed descriptions of that kind of sample. Buy or borrow a hand-lens (a reasonably good one will cost ~$35), and see if you can see any of these characteristics in your sample. I have seen a few reasonably good self-help guides for identifying rocks - choose one,  and then spend some time in the first part of the book learning rock-identifying principles.

2.      Harder Path: This is more difficult, requiring you to make more than one cold contact; it also requires you to do some significant homework up front. You could contact the geology department in a university close to you. Look for the largest university that you are willing to drive to, because you will have the best chance to find a true meteorite specialist there. Contact the geology department first to make sure you are not wasting your drive. THEN see if you can arrange to meet the geologist there who indicates that she or he feels confident enough to identify a meteorite. Keep in mind that these people have paid work they must do (such as teaching), and may not want to take the time to help. Also, geology departments are commonly inundated with people showing up and asking "what is this rock?"... so it will require patience on their part and on yours to make a connection.

Warning: One thing I would not recommend is sending a photo of the sample. No competent geologist would be willing to identify a rock from a photo alone (even if it was high-resolution, taken with a macro lens, and was crisply focused). The reason for this: to identify a rock, a geologist must be able to handle it, turn it over in sunlight looking at texture and constituent minerals, scratch mineral grains with a knife, crack the rock open to examine a fresh unweathered surface, examine it minutely with a hand-lens, etc. In most cases, a photo conveys less than 10% of the information needed to identify a rock. In many cases, even these techniques leave the identification unresolved, and thin-sections have to be cut and examined in a polarizing microscope, or a chemical analysis must be done, or both, to get a definitive answer.

Like most things of value, this won't be an easy thing for you. However, you will become a smarter and wiser person if you study this subject. Then you could go beyond that and become an amateur (meteorite, or anything else) scientist.

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Climate Change - Is It Real?

Repeatedly I have had questions about climate change addressed to me, both electronically in Ask-A-Geologist, and verbally from acquaintances  There are a lot of things floating around in the "news media" about climate change. A lot of this is correct, some of it is foo-foo, and far too much of it is deliberate obfuscation by people who have an agenda. 

There is a crude expression for scientists who sell their souls to corporations (whether Big Carbon, Big Pharma, or Big Tobacco), but this blog will not go there.

Q: Is climate change real, or is this some liberal Mother Earth Tree Hugger thing going on here?

A: A short summary of what's going on:

The Knowns:
1. Virtually all climate specialists not paid by Big Oil agree that the Greenhouse Effect is real. In fact, it was first reported in the scientific literature by Joseph Fourier (of Fourier transform fame) in 1824. It's been tested and proven repeatedly ever since.

2. There is a lot of yearly and decadal variability in climate data. Anyone can cherry-pick the weather data to prove any point they want to - but that's not science. If someone is trying to convince you that climate change is not happening, ask yourself: who's paying this guy?

3. CO2 in the Earth's atmosphere has gone from 315 ppm in 1958 to 400 ppm today (Mauna Loa observatory). Virtually all scientists with integrity accept that most if not all of this change is due to human activity. The reason? The change has been accelerating (second derivative is positive) since about 1850, when the industrial revolution really got underway. By second derivative being positive, I mean that it is ramping up faster and faster as time progresses. This is the well-known "hockey stick" graph made famous by Al Gore. Is it human caused? If we look at the carbon isotopes in this increased CO2, we can show that it is definitely caused by fossil fuel burning. 

4. The last time the atmospheric CO2 reached this level, according to the geologic record, was during the Pliocene (5.3 to 1.8 million years ago). At that time, about half of Florida was underwater (including the places where ~80% of Florida's population now lives). I've pulled Pliocene marine fossils (sharks' teeth and echinoderms) out of land deposits in Florida with my own hands; they are on my bookshelf.

5. There is a latency of CO2 after it gets into the atmosphere, and some scientists calculate this to be about 30 years. Translation: it tends to stay there. The oil you burn today will really be impacting your kids 30 years later. 

6. A gallon of gasoline, which weighs 3 kg, will produce about 10 kg of CO2. The extra comes from the oxygen you might want to breathe instead. That's 50 kilometers in my car. And that's not counting the CO2 generated to refine the gasoline. The Energy Returned on Energy Invested for Athabascan tar sands is between 4 and 7. Translation: a rather huge amount of energy is used up just getting the bitumen into the form of gasoline. 

7. Nearly 5 billion people on Earth want to have a high-protein lifestyle like their grandparents could not have even dreamed of. This means vastly-increased herds of vegetation-eating, meat-producing animals. The amount of methane a cow produces is truly breath-taking (pun intended): up to 500 liters of methane a DAY. That's more than a 5-drawer file cabinet. Methane is 37 times more potent than CO2 as a Greenhouse Gas for capturing solar heat. That's the volume of my office in CO2 equivalent - in one day.

8. Increased temperatures mean more glacier calving, more melting of Arctic, Antarctic, and Greenland ice caps. Less white stuff on the ground means the darker - light-and-heat-absorbing - under-layers will be exposed, trapping yet more solar heat and making the inevitable change non-linear. Translation: the changes will likely accelerate with time. 

It's not hard to draw some conclusions from all this:  

1. Do NOT to buy beachfront property. Anywhere. 
2. Move to the Pacific Northwest, or to the Canadian prairie provinces. They will be among the few winners of climate change.

The Unknowns:
There are several unresolved questions still:

1. How Fast:
How quickly will the global climate change consequences befall us? This speed of change has never happened before, as far as geologists can tell, in Earth's history. Predicting our future depends on climate modeling, and these models are fraught with assumptions and disagreements. However, they are beginning to coalesce, and are in general agreement. 

2. How Bad:
Likely consequences include (but these cannot be easily quantified):

• Sealevel rise... and because of tectonic settling this will be worse on the east coast of the U.S. This means more, far-reaching devastation from storms like Katrina and Sandy are in our future.
• We can expect bigger and more devastating hurricanes and tornados. If seawater rises and hurricanes grow in average size, then the storm surges they drag with them will reach deeper and deeper into the continental interiors. About 80% of humanity now lives within 100 km of a seashore.
• Greater and more terrible droughts and wildfires can be expected. Because of well-intended but ultimately catastrophic wildfire suppression policies over the past century, these fires will become truly terrible in the continental U.S., Russia, and Brazil.
• A consequence of droughts and wildfires: massive disruption in the world's food supplies.
• We are already seeing mass extinction of animal life - and explosions of other destructive types of life (e.g., jellyfish, toxic algae). The current mass extinction of wildlife (habitat destruction and over-hunting) is comparable to what the Chicxulub asteroid did 65 millions years ago.
• We are already seeing acidification of the oceans, with consequent dissolution and destruction of coral reefs, a major host of biodiversity - and the world's protein supply.

3. Is it already beyond our control?

The question has arisen: are we already at the "tipping point"? The effect of climate warming on gas hydrates (methane clathrates) that lie beneath most continental shelves is a HUGE unknown. Most estimates (from seismic reflection data) suggest these clathrates are many orders of magnitude greater than all other known hydrocarbon reserves (coal, gas, oil) on Earth combined. Gas hydrates are methane trapped in water ice below ~300 meters of seawater. This is the depth where the pressure and cold ocean floor temperatures currently trap them. They have accumulated there over millions of years from dying sea-life that drops to the bottom (some may derive from oil and gas deposits below them). A single cubic meter of these "gelids" can produce up to 180 cubic meters of methane - the internet is replete with photos of "ice" that is burning. The hydrocarbon-poor Japanese are pouring huge resources into extraction technologies right now. A crucial unknown question: will attempts to extract this stuff sort of "open the doors" to vast quantities of methane breaking out into the atmosphere?

The gas hydrates/methane clathrates issue leads to inevitable questions about non-linearity in climate forcing - and tipping-points. In other words, can things get out of control? Is it already too late - will we see a runaway temperature rise? Will we see inundation of most of the world's great cities (a real Waterworld)?


The geologic record says yes - it's happened before for natural reasons - but the geologic record also shows that the Pliocene warm period came on far more slowly than what we are seeing in the modern world climate: it took hundreds of thousands of years to raise CO2 levels then - as fast as humanity has done in the past half century.

We are already in unknown territory, and precise predictions are probably not going to be correct.  
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Castastrophes and Mass Extinctions - Periodic?

From T.S. Elliot's The Hollow Men:

This is the way the world ends

This is the way the world ends

This is the way the world ends

Not with a bang but a whimper.

Actually, it will probably be a slow bang. 

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Q: At the Ask-a-Geologist desk, we have received quite a number of end-of-the-world queries. These could be consolidated into a single sentence with two parts: 

Are mass extinctions real, and will another one happen soon?

A: There has been accumulating evidence over the past century that animal life on Earth has been decimated repeatedly. The biggest extinction events:

• ~440 million years ago (the demise of the Bryozoa, among other fossil species, marking the end of the Ordovician period),
• 251 million years ago (the “Great Permian Extinction” that saw the disappearance of over 95% of all genera living at the time including the Trilobites),
• 219 million years ago (the end of the Carnian stage in the late Triassic period, coincident with the appearance of the huge, ~85-km Manicougan craters in Quebec, Canada),
• 65 million years ago (the end of the Cretaceous period and with it most of the dinosaurs), sometimes called the Chicxulub event for a village in northern Yucatan, Mexico.
• 33 million years ago (The demise of the Cassidaria family of mollusks near the end of the Eocene, after horse ancestors first appeared),
• 2.6 million years ago (the boundary between the Pliocene and the Pleistocene epochs)…
• …and 40,000 and 12,000 years ago.

What could possibly cause all these extinctions?

In the past century geologists have come to realize that the Earth’s crust doesn’t change gradually, either, but instead it apparently evolves episodically. This takes two general forms: asteroid or comet impacts, and episodic convulsions of the Earth’s deep interior. 

The first possible reason for extinctions: asteroids or comets.

For some time astronomers have known about a 26-30 million year cycle of the Solar System, oscillating in and out of the plane of the galaxy as it revolves around a supermassive black hole at its core (Sagittarius-A* in the center of the Milky Way). There is a very rough (in other words, very arguable) periodicity in asteroid impacts mapped in the Earth’s crust. 

The thinking goes something like this: as the Solar System passes through the plane of the Galaxy, there are close approaches by other stars, which disturb the previously-stable orbits of Oort belt objects. These are icy planetesimals orbiting far beyond Kuiper Belt objects such as Pluto and Sedna, reaching out to 50,000 astronomical units from the Sun (up to a light year). The Oort belt is where most of the comets come from. Thus, a disturbance out at this distance could send one or more into the inner Solar System. These may directly impact the Earth, or may disturb or deflect one or more asteroids orbiting between Mars and Jupiter. Asteroids are far more common in the mid-to-inner Solar System, but comets generally have a much high relative velocity with respect to Earth. Since kinetic energy goes the mass times the velocity squared, a comet could potentially do quite a bit more damage for the same size if it impacted the Earth.

For more than a century scientists have been aware of these extinctions in the paleontological record. The cause of the great Permian Extinction of 250 million years ago is still not fully understood, but may be related to huge seafloor craters now known to exist off the northwest coast of Australia (Bedoubt) or the Falkland Islands east of Argentina. The extinction of the dinosaurs 65 million years ago actually has a 'smoking gun': a huge, 150-to-180-km crater now lying beneath the northern edge of the modern Yucatan Peninsula of Mexico. There is other evidence: ginormous tsunami deposits elsewhere in the Caribbean including Haiti, a tektite strewn field throughout the American southeast, and distinctive fragments found in Montana and eastern Pacific ocean deep-sea drill cores.

Keep in mind that the Earth’s crust is a very dynamic place; while we see thousands of craters on the Moon, we see few on the Earth. Careful mapping has identified only 170+ asteroid-impact craters on the Earth, even counting the tiny ones like Wabar in Saudi Arabia, and Henbury in Australia. The Earth’s crust is evolving constantly because of plate tectonics and weathering, so evidence of impacts is steadily being erased.

The second possible reason for mass extinctions: gargantuan volcanic eruptions. 

A recent article in EOS, the Transactions of the American Geophysical Union (Rampino and Prokoph, EOS 94, No 12, 19 March 2013, p. 113-114), points out that there have been roughly cyclic episodes of large igneous provinces (LIP’s). The Deccan Traps, making up much of western India, is one of these provinces: kilometers-thick, continent-sized basalt flows all erupted over a fairly short window of time. A vast basalt province in Siberia called the Siberian Traps, and the huge Columbia River basalts are among the others. These are thought to be the result of large upwelling mantle plumes; for scale imagine the eastern US being covered by miles-thick flows of basaltic lava.

The geologic record shows these LIP’s to have occurred around

• 390 million years ago
• 295 million years ago
• 250 million years ago (the Siberian Traps)
• 200 million years ago
• 185 million years ago
• 135 million years ago
• 100 million years ago
• 65 million years ago (the Deccan Traps occurred close to the Chicxulub impact, causing some confusion about the relative effects of the two events)
• 30 million years ago
• 17-14 million years ago (the Columbia River Basalt province).

From these ages frequency-domain filtering (and your eye if you plotted them out) suggests an apparent rough cyclicity of 28-to-35 million years, especially prominent starting 135 million years ago.

When volcanic centers this size erupt, there is a huge degassing process associated with it: sulfur dioxide and vast amounts of carbon dioxide are released. When Mount Pinatubo erupted in 1992, it sent a proportionally smaller cloud of SO₂ into the stratosphere – and the Earth’s average temperature cooled for two years afterwards. And that's just from what happens in the stratosphere.

Could there be a third reason for mass extinctions? 

Around 40,000 years ago, most of the large animals of Australia abruptly disappeared. These include the rhino-sized, wombat-like marsupials called Diprotodons, giant 200-kg kangaroos, a goanna bigger than the modern Komodo dragon, a giant goose-like bird twice the size of the emu, and many others. These animals had survived at least two episodes of climate change prior to 40,000 years ago. In North America about 12,000 years ago, most of the large “charismatic megafauna” of North America (mammoths, giant sloths, camels, cave bears, saber-tooth tigers, etc.) suddenly disappeared. In both cases, these mass extinction events (and a more recent event on Madagascar that is still very much on-going) correlate closely with the arrival of the human species in these regions. The implication of overhunting is hard to miss here. As the human population surges past 7 billion today, the largest mass extinction in the past 65 million years is fully underway, and the Passenger Pigeon is just the first and most obvious victim. Habitat loss, overhunting, and accelerating climate change are the proximate mechanisms for this current and stunningly rapid mass extinction event. 

The End of Things As We Know It

There are Near Earth Objects (NEO’s) out there that NASA and the US Air Force are monitoring (the number keeps growing, but at least the search process is now automated). Based on their known sizes (we can generally only see the big ones) and what happened at Chicxulub 65 million years ago, most of these could wipe out human civilization as we currently know it... not if, but when, one hits us. 

If Yellowstone (just one of several known supervolcanoes) unzipped tomorrow, it would cover the eastern two thirds of the United States with a vast blanket of ash, suffocating all living things. The gas and peripheral consequences would devastate the entire planet. To put things in perspective, the last eruption 640,000 years ago left an off-white layer 20 meters (65’) thick called the Pearlette Ash Formation near Colorado Springs… 800 miles away. I have personally pulled a camel’s tooth from the bottom of this formation.

However, the problem may be more imminent. 

As Pogo said, “We has met the enemy, and it is us.”

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