Now I realise that many of my readers are experienced scientists with either undergraduate degrees or published research papers behind them, and this article is not for you. For those of you out there who may have a passing interest in science or geology and find yourself intimidated by the overwhelming barrage of terminology I tend to stuff into my articles, I thought I’d lay out some basics for future reference.

Today, it’s a pretty easy concept with far reaching and extremely important consequences, and that is the concept of an isotope.

Hopefully you know what an atom is. If not, there’s plenty of resources online to help you. Every atom, except your standard Hydrogen nucleus, contains both positively charged protons and neutrally charged neutrons. The chemical element an atom is, is dependent entirely on the number of protons. Hydrogen has one proton, Helium 2, Lithium 3, for example. What can vary, however, is the number of neutrons, and this variation in neutrons in an atomic nucleus is what defines an atom’s isotope.

Take Helium for example. Your standard Helium atom, such as the one many people would have inhaled, contains two protons (making it Helium) and two neutrons. This combination makes it a ⁴He, pronounced “Helium 4,” isotope. It’s 4 because that’s the total count of protons and neutrons in the nucleus: 2 protons + 2 neutrons = ⁴He. The nuclei of these atoms can be visualised like this (blue are neutrons, orange are protons):

Helium also comes in the form of ³He, which has two protons and one neutron. How and why there are different isotopes is due to the process which formed the atom in the first place, be it a big bang, the nuclear decay of bigger atoms, or the fusion of smaller atoms (in this case, two hydrogen atoms will fuse, in a process, to form Helium). ³He can be visualised like this:

Both ³He and ⁴He are what’s know as stable isotopes. This means they’re quite happy sitting in the 3 or 4 isotopic states for ever and ever without decaying, i.e, having sections of the atomic nucleus splitting away. Helium has 8 know isotopic states, but none of these 6 other isotopic states are physically stable, and tend to split into lighter Helium isotopes and eventually Hydrogen and a hail of neutrons after a very short amount of time. ⁵He, for example, has a halflife (the time it takes half of any given quantity to decay away) of 0.7 zeptoseconds, which is 7×10^-22, or 0.0000000000000000000007 seconds. That’s incredibly quick, meaning ⁵He, whenever it happens to form, isn’t around long enough to do anything before effectively exploding into two Hydrogen atoms.

These unstable isotopes, such as ⁵He or ²⁶Al (Aluminium is stable with 13 protons and 14 neutrons, i.e, ²⁷Al) and big, heavy elements like Uranium and Plutonium (which are unstable simply due to their large nucleus size) are not able to hold together their atomic nuclei and after a time, each atom does something called decay – i.e, split into smaller atoms by radiating away parts of their atomic nucleus (hence, nuclear radiation). This is the basis of nuclear power – as the splitting of Plutonium, Uranium and Thorium atoms into smaller atoms releases a lot of energy.

And this is where the really useful part of isotopes comes from. The decay of unstable isotopes is constant, predictable and measurable. After 0.7 zeptoseconds, half of all ⁵He atoms produced 0.7 zs previously, would have decayed. Guaranteed. So if you know the ratio of ⁵He produced in a reaction in relation to the quantity of something stable like ⁴He, produced in that same reaction, and you can measure them both, you can very easily work out how long it’s been since the reaction took place. That’s the basis radiometric dating, and the subject of a future science basics post.

This week’s episode discusses hidden mountains in Antarctica, bacteria living high atop the Andes, panspermia and extraterrestrial life and more.

Participants (links in brackets are Twitter feeds)

Chris - goodSchist (@yorrike)

Chris –  Highly Allochthonous (@allochthonous)

The Gamburtsevs Mountain Range and Antarctica

The BBC News article “‘Ghost peaks’ mapped under ice” is a nice summary of the story. New Scientist article has additional information in the article “Alpine mountain range revealed beneath Antarctic ice.”

And as always, there’s a little more information at Wikipedia on the GamBurtsevs Mountain Range.

Here’s some information about Lake Vostok.

And you can read about the International Polar Year at Wikipedia.

Extremophile Bacteria at the top of the Andes

Have a read of Science Centric’s Article “Earth’s highest known microbial systems fuelled by volcanic gases.”

NASA’s Kepler Mission

There’s the Wikipedia page on Kepler and the NASA’s official Kepler Mission page too. Plus there’s an example of the mass media misinterpretation from the BBC.

And Venetian resurfacing I was talking about is detailed  in this interview with David Grinspoon “Venus (and Earth) Resurfaced in a Single Catastrophic Event?” and in the paper Catastrophic Resurfacing and Episodic Subduction on Venus from Science Direct. This episodic resurfacing is still up for debate, though, and The Imperial College in London has a counter view.

Exbiology, Panspermia and Planetary Geology

Titan is Saturn’s moon with methane oceans.

Europa is the Jovian moon (beware the obelisk).

You can read about the Dawn Mission at NASA’s official site, or there’s the Wikipedia entry.

My article on Ceres, Dawn and (no) Panspermia (containing information on Ceres, 4-Vesta, the HED meteorites and the Murchison meteorite). And the offending article on The Universe Today.

There’s information about the bacteria on the Moon

Dave’s article on resurrected Eocene yeast and the resulting beer.

The Allan Hills 84001 was the one with the bacteria-looking inclusion in it.

Mars had recent running water and there’s Google Mars to have a look at too.

del.icio.us/podclast

We have a del.icio.us account which can be found at http://del.icio.us/podclast. All the web pages and resources we’ve found and used in the discussions on the podclast can be found here. A convenient way to browse per episode is to go to, for example, http://del.icio.us/podclast/episode8 (for this episode).

If you find a link to a topic that you’d like to hear discussed on the podclast, or have a link to a topic that’s already been discussed, you can add links to the podclast page through your own del.icio.us account.

When saving a link, include the tags for:podclast and episodeX (where X is the episode number – for example episode8). You can add more than one episode tag if the link applies to multiple episodes.

Next Episode

We like to have a new episode of the podClast every fortnight, so the next episode will be recorded on Sunday the 22nd of March at 2000 GMT.

Contributing

If you’re keen to hear a specific topic talked about, or would like to join the discussion during the next episode, either leave a comment below or email chris [the at symbol] goodschist.com. You’ll probably also do well reading the details on joining the podclast. If you don’t have the time to join us but would like to contribute a 3-5 minute audio clip to the show simply record it, make sure it’s an mp3, and send it to the address above.

Credit

The intro and exit music was Roots Fi Cool by Burning Babylon.

Text Addresses

The post that accompanies this podcast can be found at http://www.goodschist.com/2009/03/12/the-podclast-episode-8/ or http://is.gd/n2PW and an archive of all  podClasts can be found at http://www.goodschist.com/category/podclast/

It’s pretty staggering how old these rocks are. So let’s put it into perspective:

These rocks were formed 270 millions years after the Earth (4.55 Ga), which means they’ve remained reasonably unchanged for almost the entire history of the planet. They’ve survived 4.28 billions years of: plate tectonics including subduction and obduction, glacial erosion, meteorological erosion, chemical erosion, chemical alteration (maybe), or any other method of rock recycling. It also means we have pushed back the earliest date for continental material existing on Earth by 250 million years (the previous record was 4.03 Ga for the Acasta Gneiss, also from Canada).

These aren’t the oldest terrestrial material ever discovered, however. That title still belongs to zircons from the Jack Hills in Western Australia, that have been dated at a positively geriatric 4.4 GYr. But as a sample of rock, this is pretty exciting so far as early Earth chronology goes.

Geological timescale thanks to Chris Rowan at Highly Allochthonous.
Splash image to the left lifted from Nature, and courtesy of AAAS/Science.

Chondrites & Carbonaceous Chondrites

Figure 1. A slice of the NWA 2364 CV3 carbonaceous chondrite, with a white CAI visible in the top left. The CAI is ~5 mm across the longest axis. This is one of the CAIs I used for my MSc research. Click to enlarge.

Chondrites are ancient stoney meteorites and direct remnants of the processes that formed the solar system. Broadly ultramafic in composition, they contain mostly iron, magnesium, silicon and oxygen (Scott & Krot, 2004). They were originally named due to the high concentrations of chondrules, mm-sized spherical droplets of silicate glass with minor metal and sulphide contents. There are plenty of chondrules visible in Fig. 1, they’re the red/brown/black circles that make up a large portion of the meteorite slice. The important thing about chondrites is they have not experienced the alteration you’d expect where they part of a planet with sufficient mass to begin differentiating. That is, forming a crust-mantle-core configuration like the terrestrial planets.

The chondrite above is what’s known as a carbonaceous chondrite. The name carbonaceous chondrite is a bit misleading, as this class of meteorite are not universally rich in carbon. The defining property of these carbonaceous chondrites is that they contain concentrations of refractory lithophile elements, such as the Rare Earth Elements (REE), that are equal to or exceed that of the Ivuna-like sub class. That equal to part means that Ivuna is also classified as a carbonaceous chondrite.

Ivuna and Ivuna-Like Chondrites.

Table 1: Data on the types of carbonaceous chondrites. Adapted from Scott & Krot (2004) with additional data from Greenwood et al. (2004). Click to enlarge.

Ivuna was a witnessed “fall” which landed in Tanzania in 1938 as a single 705 g stone. As it was the first meteorite of its type classified, the Ivuna-like group (CI) is named after it.

The Ivuna group is comprised of the Ivuna, Orgueil, Alais, Tonk and Revelstoke meteorites, making up a total of ~3% of discovered carbonaceous chondrites (Table 1). Whether this is indicative of the true proportion of meteorites or not, is up for debate. Ivuna is reasonably fragile, and if a sample makes it through the atmosphere, it faces the prospect of erosion, due to the Earth’s helpful weather systems. The proportions of all samples shown in Table 1, therefore, could be indicative of the proportions of the particular types of meteorites, or simply indicative of the likeliness of each type to survive passage through the atmosphere and/or erosion before being discovered.

Ivuna has very low refractory inclusion (RI) and chondrule concentrations relative to other carbonaceous chondrites. Refractory inclusions include Calcium-Aluminium Inclusions (CAIs) and Ameboid Olivine Aggregates (AOAs).

Why a Sample with Solar Composition is Useful

The sun makes up a total of 99.8 % of the Solar System’s mass, a lion’s share of the material that constituted the original solar system. It’s therefore perfectly reasonable to assume the Sun is representative of the original composition of the gaseous pre-solar nebular the planets, plutoids, moons, meteorites and you and I formed from. And though you can make pretty good measurements of solar composition using spectral analysis, there’s nothing better than having a nice big chunk you can chip a little of into a mass spectrometer. This has the distinct advantage of allowing geochemists to determine the isotopic, in addition to elemental, composition.

Isotopes are important because the cloud the solar system formed from, was generated by a supernova or supernovae, generating huge quantities of stable and radioactive isotopes. Many people in the western world will have direct experience with some of these radioactive isotopes – Uranium and Thorium are the elements on which all nuclear power technology is built. So switching on a light in places is almost directly extracting power from a supernova.

Magnesium, for example, has 3 stable isotopes: 24Mg, 25Mg and 26Mg. The latter of those isotopes, in addition to being a stable isotope produced in supernovae events, also happens to be the daughter product, or the left over material, following the radioactive decay of the short-lived isotope 27Aluminium. 27Al has a half-life of ~700 KYr and when it decays, it produces heat, and lots of it. Knowing how much heat the pre-solar nebula cloud was producing, in addition to the heat-input from the young T-Tauri Sun, is important in understanding how refractory inclusions like CAIs, chondrites, planetesimals and eventually planets, formed. So Having a hand sample of the material that started it all, lacking the more volatile elements such as Hydrogen and Helium, of course, let’s us build a model for where and when things formed in the Solar System.

Figure 2: Generalised Rare Earth Element proportions in refractory inclusions, normalised to the bulk concentrations in Ivuna. Adapted from Taylor (2001). Click to enlarge.

Fig. 2 is a good example of the CI bulk composition being used as a standard. It shows generalised plots one should expect from the Rare Earth Elements (REE) in refractory inclusions, such as the CAI in Fig. 1.

Why Ivuna is so Important

Ivuna is important because it is a sample of the bulk Solar System. Unlike CV (Vigarano-like), CK (Karoonda-like) or CM (Murchison-like) chondrites, which are all enriched in refractory elements, Ivuna is pristine insofar as bulk concentrations go. Containing a bulk composition in close proximity to that of the Sun lets you measure just how enriched those aforementioned meteorites are, in direct comparison to the solar system.

CV3 chondrites, for example, contain a large number of refractory inclusions (Table 1), named so because of their enrichment in refractory elements. Those being elements which very high melting and boiling points. That means the highest condensing temperatures too – making them the first elements to condense out of a hot nebulous cloud. Due to the presence of those inclusions, CV3 chondrites are enriched, in bulk, in the refractory elements relative to Ivuna, and therefore the solar system. Knowing this lets you make the assessment that CV3s, or at least the refractory inclusions contained within, formed in conditions that were much hotter than those in which CIs formed. And since this is the early, hot solar system we’re talking about, that means they formed earlier (this is also confirmed by the elevated level of 26Mg, also in relation to those in Ivuna, and good old-fashioned absolute Pb-Pb dating).

The comparisons don’t stop with meteorites, though. CI concentrations are the values many geochemical systems are normalised to (that’s when you divide the value you have in your sample, by the value measured in the standard), allowing for a comparison with the solar system. Any deviation away from the bulk solar system composition denotes a chemical process has taken place, and can tell a story of heat, pressure or aqueous alteration.

Using the most modern equipment, the new samples available from the Natural History Museum purchase will better refine the standard measurement values we have. This will, in turn, allow for higher precision geochemical comparisons and potentially allow us to refine or rethink our models as to how the solar system formed and why the planets, like Earth, got to be the way they are.

References

Greenwood, R., Franchi, I. A., Kearsley, A. T., & Alard, O. (2004). The relationship between CK and CV chondrites: A single parent body source? Lunar and Planetary Science, XXXV.

Scott, E. R. D., & Krot, A. N. (2004). Chondrites and their Components. In A. Davis (Ed.) Treatise on Geochemistry, vol. 1: Meteorites, Comets and Planets, chap. 1.07, (pp. 143–200). Elsevier Ltd.

Taylor, S. R. (2001). Solar System Evolution A New Perspective. Cambridge University Press, 2 ed.

Episode 5 of the podClast is ready for download. You can grab the mp3 here (19.1 Mb, 33:18), or subscribe through iTunes here.

Today’s show discusses The Mars Phoenix Lander,

Participants

Chris – goodSchist

Jess – Magma Cum Laude

Show Notes

Notes on taming volcanoes with limestone and dolomite

There’s images from the Phoenix showing grains from the Martian surface.

Big Earthquakes Spark Jolts Worldwide? We had a discussion about that.

Ice quakes are a topic you may like to read about.

I managed to digress into talking about the ANDRILL project.

There’s the Geotimes article and the AAPG article about geoblogging. And Chris has a list of all the active geobloggers over at Highly Allacthonous. There’s also Aiden’s post about it all.

And here’s the link to the call for posts for the Accretionary Wedge #10.

Jess was right with her first guess, it was Tambora that caused the year without a summer (not Krakatoa). And the artist we couldn’t remember the name of was James M. W. Turner

del.icio.us/podclast

We have a del.icio.us account which can be found at http://del.icio.us/podclast. All the web pages and resources we’ve found and used in the discussions on the podclast can be found here. A conveniant way to browse per episode is to go to, for example, http://del.icio.us/podclast/episode5 (for this episode).

If you find a link to a topic that you’d like to hear discussed on the podclast, or have a link to a topic that’s already been discussed, you can add links to the podclast page through your own del.icio.us account.

When saving a link, include the tags for:podclast and episodeX (where X is the episode number – for example episode5). You can add more than one episode tag if the link applies to multiple episodes.

Next Episode

We like to have a new episode of the podClast every fortnight, so the next episode will be recorded on Saturday the 21st of June at 2300 GMT.

Contributing

If you’re keen to hear a specific topic talked about, or would like to join the discussion during the next episode (we’d really like a few more voices in there), either leave a comment below or email chris [the at symbol] goodschist.com. You’ll probably also do well reading the details on joining the podclast. If you don’t have the time to join us but would like to contribute a 3-5 minute audio clip to the show simply record it, make sure it’s an mp3, and send it to the address above [I'll add more thorough instructions at a later date]

Credit

The intro and exit music was Roots Fi Cool by Burning Babylon.

The splash image on the homepage is a section of the painting “The Fighting Téméraire tugged to her last Berth to be broken up” by J. M. W. Turner and the album art is from NASA.

I’m obsessed with science. However, once I’m done with my MSc, I’m off into the workforce for a time (potentially a long time). I haven’t ruled out diving into a PhD at some point, and in the mean time I want to continue to stay abreast with current research and I want to talk about research on this blog. Though subscriptions to the usual suspects (Nature and Science) aren’t out of my grasp, accessing articles from large journal databases such as Elsevier‘s Science Direct will cost me US$30 per journal article. And frankly, that’s just ridiculous. I know how much work goes into research papers – but $30 each? So far as I’ve been able to tell, research isn’t funded from journal sales.

So, my question to the geo-blogosphere, and the science blogosphere in general is, what’s the best way of getting full-text journal papers from a range of publications for reasonable money when you’re not within easy reach of a university or well-equipped public library? Preferably without resorting to illegality.

Update: In a case of blissful geoblog serendipity, Andrew Alden of About: Geology has just published a blog entry on open online journals within minutes of me publishing this article. Do great minds ponder alike?

In the image, from south to north are Mt Ruapehu, Mt Tongariro and Ngauruhoe, the volcanics associated with Lake Taupo (a caldera lake), the volcanics associated with Lake Rotorua, White island and then a string of sub marine and sub aerial volcanics that make up the Kermadec arc. All of these are marked with red stars. The white arrow-line shows the subduction trench that’s the result of the Pacific subducting underneath the Australian plate. The orange triangle is the outline of the Taupo Volcanic Zone. Then there’s Mt Taranaki marked with a “?“. It is this particular andesitic volcano that makes me, and many, many others go “hmmm”.

[Show as slideshow]

It’s a rather large feature (see satellite imagery above. The dark green is the rough outline of the surrounding national park), having produced a classical almost-circular flank. It’s still active (last eruption, though minor, was around 1800), and it’s young, having commenced eruptive activity ~130 Ka. The really weird part is, it’s not geographically in-line with the rest of the TVZ volcanics, being ~100 Km west of the TVZ (even Maori legend makes note of this). And it’s not geochemically linked with the TVZ, being enriched in Potassium and other Large Ion Lithophile Elements. For a volcanic zone that’s popped up through an established continent, it’s also rather lacking in enriched, assimilated continental material, resulting in a fractionated elemental makeup (Here’s a thorough Journal of Petrology article detailing Taranaki and contrasting it with Ruapehu). But the big question that really gets to me, and one I haven’t found a satisfactory answer to is; why is Taranaki there at all?

You can check out other “geohmmms” at this month’s Accretionary Wedge.

Images in this article were taken from Google Maps and Wikipedia.

But to be clear, what defines an epoch, an age, a period and era or an eon in the geological sense is reasonably arbitrary. There is nothing in particular one must consider as a marker between two periods. Time periods can be determined as the time when a particular large group of biota become extinct (like the P-T extinction event) or when there’s enough cooling for rocks to form and then for some of those rocks to still exist (like the Hadean-Archean boundary). A geological time is defined by geologists saying “that’s a good point right there because of this”, and nothing more. Brain at Clastic Detritus has an article expressing how annoyingly wrong a news article got this particular point.

In his latest article, The Anthropocene revisited, Andrew Alden takes another look at the concept of recognising the remarkable changes the human species has had on the geological record as a new geological epoch (Universe Today also has a good article up on this topic). The concept of the Anthropocene, as originally suggested by Nobel Prize-winning chemist Paul Crutzen in 2002 is discussed in a (freely available) GSA Journal paper entitled “Are we now living in the Anthropocene“, which I quote below;

A case can be made for its consideration as a formal epoch in that, since the start of the Industrial Revolution, Earth has endured changes sufficient to leave a global stratigraphic signature distinct from that of the Holocene or of previous Pleistocene interglacial phases, encompassing novel biotic, sedimentary, and geochemical change.
Zalasiewicz et. al., 2008

The current “sixth mass extinction” event we are causing started in the Holocene, the epoch that is defined as the 10,000 carbon years preceding 1950 (Zalasiewicz et. al. 2008, Wikipedia). This was the end of the Younger Dryas, the name given to the last ice age, and saw the beginning of the widespread extinction of mega fauna such as the Mammoth and the last Saber Tooth Tiger species. This, much like the extinction event at the Cretaceous-Tertiary boundary, began and continued slowly (in human terms) until a single event established it as a true geological boundary (and I’ve discussed this particular point before). It was a slow process. It began slowly (say, over a period like 10,000 years), and then ended suddenly (over a few months, but a few decades is basically the same in geological terms).

Though establishing a new epoch is probably best in terms of scientific enquiry, it would make the dawn of human domination of the Earth (the Holocene) a separate epoch from the widespread changes that domination brought with it. And if you consider the human phenomenon as a single natural process, it may make more sense to consider the beginning, duration and end as a single time period. And not to put too finer point on it, I think the amount of change currently occurring is so dramatic that establishing a new epoch maybe underplaying it. Should we begin to consider the establishment of a new Period once we can no longer sustain ourselves to cause as much change as we are currently? That being said, I’m in favour of considering everything since a yet-to-be decided point (and by point, I mean a very precise, slightly un-geological point, like new years eve 1850), as a new epoch, even if it does make the Holocene the shortest geological epoch ever. To be fair, I’m more interested in pre-Hadean events than the latter parts of the Quaternary.

References

• Zalasiewicz J, Williams M, Smith A, Barry TL, Coe AL, et al. (2008) Are we now living in the Anthropocene. GSA Today: Vol. 18, No. 2 pp. 4–8