Nature Podcast 8 June 2006

Introduction

This is a transcript of the 08 June edition of the weekly Nature Podcast. Audio files for the current show and archive episodes can be accessed from the Nature Podcast index page (http://www.nature.com/nature/podcast), which also contains details on how to subscribe to the Nature Podcast for FREE, and has troubleshooting top-tips. Send us your feedback to mailto:podcast@nature.com

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Chris Smith: This week clues to the origins of planets and asteroids have been found lurking in a dusty disc around a nearby star, researcher uncover signs of the earliest life on Earth and dwarf dinosaurs have turned up in Germany. More on these stories shortly. Hello. I'm Chris Smith and welcome to this week's edition of Nature's Podcast.First up this week we're shaking up the world of seismology and trying to get to the bottom of where aftershocks come from. These are the secondary movements that are triggered by an earlier quake and they can occur at considerable distances away from the primary earthquake. But why do they happen? Karen Felzer from the US Geological Survey. Nature 441, 735–738 (8 June 2006) ; Nature 441, 704–705 (8 June 2006) |

Karen Felzer: Our main discovery is that aftershocks, which are the earthquakes which follow a large earthquake are triggered by dynamic stress which is the shaking that you actually feel in an earthquake as opposed to static stress change which is a smaller, permanent stress change caused by the movement along the fault surface.

Chris Smith: So talk us through the actual method that has led you to coming to the conclusions that you have.

Karen Felzer: So, the data that we worked with in California was a very special dataset, which was created by Peter Shearer and his colleagues and these were earthquakes which have been carefully relocated, which means they went back, they took all the original data and they tried to get very precise locations for these earthquakes. With this information, we took thousands of main shocks and for each one we found its aftershocks over a very short time period and looked at the distances between the main shocks and the aftershocks. We then made a graph, which showed the density of aftershocks as a function of distance from the main shock fault. Once we had this graph we could see whether this was a continuous function at the near field and the far field or whether there was a discontinuity. And the importance of this is that a continuous function indicates a single physical mechanism. So there's just one kind of physics that would be triggering all the aftershocks, whereas a discontinuity would indicate that maybe we have one physical mechanism in the near field and another physical mechanism in the far field.

Chris Smith: And what did you find?

Karen Felzer: We found that it was a single continuous line and the fact that this decay was so continuous and so smooth led to the conclusion that there must be a single mechanism that was triggering all these aftershocks. We know that static stresses decay much faster than dynamic stresses do and so in the far field, because the static stresses are so small and the dynamic stresses are much larger, we're able to know for sure that the dynamic stresses are triggering the aftershocks and since we have this other finding that the physical mechanism in the far field and the near field must be the same or is probably the same this allowed us to imply that the dynamic stress, so the actual shaking, was triggering aftershocks at all of the distances.

Chris Smith: Karen Felzer. But what's the significance of this result and, indeed, are we any closer to the seismic Mecca of being able to predict earthquakes and the location of their aftershocks? Here's co-author, Emily Brodsky.

Emily Brodsky: Until extremely recently we didn't actually know what earthquakes were really well. We've had somewhat embarrassing error bars on our earthquake locations, half a kilometre, kilometre kind of errors. And if that was your error then there's no way you could do a very precise study of the density of aftershocks as a function of distance from the main shocks you don't even know where your earthquakes are so there've been some real advances in the technology of earthquake location and it's really because of these advances in location that we're able to make this observation that really wasn't possible ten years ago.

Chris Smith: Are we any closer to arriving at a situation of being able to predict when an aftershock and where an aftershock might take place following a main earthquake, which is of course going to be the key question that people want you to answer "yes" to?

Emily Brodsky: I won't answer yes but what I will say is one of the key predictions from our studies is that the probability of having an aftershock is proportional to the amplitude of the shaking. So if you know the amplitude of the seismic waves coming in you can, in a probabilistic sense, predict whether or not there's going to be an aftershock at a given site. And that's a very strong prediction that is going to need to be tested by future sub studies. We need to understand what this physical process is that starts an earthquake from the shaking but if it turns out to be correct that has implications for short-term hazard prediction.

Chris Smith: It's tempting to call that an earth shattering result. Emily Brodsky from the University of California at Santa Cruz.Now, who would have thought that smelling a newly fallen meteorite could give you clues about its origins? But that's one approach to solving a problem that Aki Roberge from NASA's Goddard Space Flight Centre has come up against. She's been looking at a nearby young star called Beta Pictoris, which is surrounded by a vast disc of material, similar to the protoplanetary soup that spawned the earth. But it seems there's too much carbon in it. Nature 441, 724–726 (8 June 2006)

Aki Roberge: We've discovered extremely carbon-rich gas around a nearby young star called Beta Pictoris, which is about eight to 20 million years old, which is really quite young. I mean, the Earth is 4.6 billion. And this star is surrounded by a disc of gas and dust and this material is produced by the destruction of young planetary bodies like asteroids or comets. Basically they're smashing together or evaporating and producing, you know, this gas and dust that we see.

Chris Smith: How big is this disc? Is it right up close to the star or does it go out into space a long way?

Aki Roberge: It goes out quite large, actually. It's extraordinarily large. I believe the dust disc has been imaged all the way out to, I think, about 1,000 AU from the star. So, one AU being the Earth-Sun distance.

Chris Smith: And when we're talking about a disc, and you're talking about dust, is it literally tiny particles or are we talking about huge lumps of rock here?

Aki Roberge: Well, what we see mostly is the tiny particles but we presume there are much larger bodies there, like, you know, kilometre-sized asteroids and comets. We don't really know if there are planet-sized bodies in the disc yet but we think it very likely.

Chris Smith: How are you making your measurements?

Aki Roberge: It's absorption spectroscopy basically. We look at the light from the star. Now, this particular disc, very fortunately, happens to be edge on to our line of sight. So if we look directly at the star we're looking all the way through the edge on disc and superimposed on the light from the star we see the absorption signatures of the gas that lies in between us and the star.

Chris Smith: So is this a solar system in evolution in the sense that our own solar system would have looked like this a long while ago, 4.5 billion years ago, and slowly that that debris will coalesce to form bigger bodies that will eventually become planets?

Aki Roberge: Yeah, more or less except that if the bigger bodies are going to form they've already formed. So if it does correspond to a phase that we believe occurred in the early solar system and sort of like the disc-clearing phase where it's clearing out the leftover bits that didn't get incorporated into very large bodies like planets.

Chris Smith: Are there any unexpected things lurking in that disc or things that are there that shouldn't be?

Aki Roberge: Well, yeah. There's a few things. Well, first of all, the gas that we measured is extraordinarily carbon rich. I mean, the carbon-to-oxygen ratio is 18 times greater than what's seen in the sun.

Chris Smith: So, how do you account for that?

Aki Roberge: Well, I can't account for it really. One simple possibility is perhaps the asteroids and comets in Beta Pic are just very carbon rich and perhaps their comets have methane ice instead of water ice like the ones in our solar system do and perhaps the asteroids have lots of carbon compounds and more than we think the ones in our solar system do. So that's one simple-minded explanation although how you would form such carbon rich bodies in a disc that should probably be not so dissimilar from the one our solar system is a bit of a theoretical problem. One other possibility is that asteroids are fresh meteorites, really fresh ones, right when you pick them up after they've fallen, they smell. And that smell is volatile carbon compounds like benzenes and stuff like that and they have some trace amounts of these volatile carbons. Perhaps the asteroids in Beta Pictoris are selectively losing their volatile carbon, they're selectively out-gassing it, the volatile carbon, and so perhaps when Solar System asteroids were younger they had a great deal more of this volatile carbon.

Chris Smith: The sweet smell of success or, at least, just a meteorite. That was Aki Roberge from NASA's Goddard Space Flight Centre who's carried out the most detailed analysis yet of the protoplanetary disc around a nearby star.Shortly we'll be winding the clock back to prehistoric Germany where palaeontologists have uncovered a population of dwarf dinosaurs and we'll also be meeting some of the first life on Earth but before then and with a look at what's going on in the news this week here's Nature's Alex Witze talking to Anna Lacey.

Alex Witze: Thanks. We've got three stories this week. The first is about Australia's big research organisation, the CSIRO. They've been getting hauled in front of the Australian parliament and asked some tough questions recently. They're projecting that they're not going to make quite as much money in the future as before and there've been some questions about where that money is coming from and where it's going to be going in the future. Nature 441, 674–675 (8 June 2006)

Anna Lacey: So how much money are we talking about here?

Alex Witze: It's not a huge amount of money. It's, essentially, 184 million over the next four years. That compares to about $1 billion that the CSIRO goes through every year.

Anna Lacey: So where's this money been going then?

Alex Witze: Well, the organisation has some good answers as to where it's been going. A lot of it has to do with stuff coming into the organisation that's not cash. For instance, industry might contribute some people to laboratories or send along some equipment and that's a contribution to the agency but it's not money in the bank, so to speak. So they say they're still getting as much as they have before. It's just the accounting practices that have a lot to do with the shortfall.

Anna Lacey: And hasn't some been going on entertainment funds?

Alex Witze: Yes. They have this lovely hospitality fund, which racked up something like AUS$1.4 million last year, which sounds like quite a lot. There's also been $750,000 spent on renovating the chief executive's house. But the agency says, of course, it had lots of good reasons for these expenses. The hospitality bill, they say, isn't taking people out and wining and dining them. It's just coordinating people, researchers to get together. The financial officer for the organisation said, well, we don't get them fine wine. We may give them a cup of tea but we try and get them together.

Anna Lacey: So what are the CSIRO going to try and do now to try and pull themselves out of this situation?

Alex Witze: That's an excellent question and a lot of it will have to do with how accountable they're held in the parliament. The opposition party in parliament has been calling for, essentially, a top to bottom re-evaluation of how they do things so we'll see what happens and keep an eye out for how they respond to this kind of pressure.

Anna Lacey: But it's not just the directors of the CSIRO that are coming under fire from questioning this week.

Alex Witze: That's right. Scientists who also study some endangered marine mammals in the western US are also under fire, you could say. They are getting in trouble or, essentially, having their research shut down for some research practices they've been doing on Stellar sea lions which are endangered, especially along the western US and up into the Alaskan coast. Every year there's a big research effort where a whole bunch of researchers go into the field and try to identify the sea lions and figure out where they're mating, where they're travelling, all that good endangered species type stuff. And one of the identification measures they use is they brand the pups. So you get a baby sea lion and you brand it with a hot brand. The Humane Society, obviously, have been up in arms about this, sued the US government and now the government has shut down the research programme for the year. Nature 441, 677 (8 June 2006)

Anna Lacey: What's the evidence that's raised these concerns that the branding is really having a detrimental effect on the sea lions?

Alex Witze: Well, it's a very contentious issue because obviously the Humane Society has its own sort of agenda and the researchers have theirs as well. Some of the researchers say that after the pups are branded they look very healthy and strong. The Human Society will point to certain types of data that say more pups die after you brand them than if you don't brand them.

Anna Lacey: But aren't these scientists keeping a track somehow and looking to see exactly what the effects are?

Alex Witze: Well, that actually is the heart of the lawsuit because the lawsuit that the Humane Society brought said, essentially, that the US government was not doing enough follow up studies to see how things were going on. And that's what the federal judge who made this ruling recently agreed on is that, yes, you need to go back, you need to do more studies on exactly the effects of these studies on the sea lions.

Anna Lacey: So how's this ruling going to affect the scientific research into sea lions for the foreseeable future?

Alex Witze: Well, what it means is it's essentially shut down for the year and this is a huge federal programme. Something like 120 million over the past couple of years has been poured into this. So it's anyone's guess to see whether it's going to get reinstated next year and, if so, whether there'll be any new restrictions on the kinds of studies they can do.

Anna Lacey: Okay. Well, finally, this week it seems that the days of tricky lab protocols may be over?

Alex Witze: That's right. For those researchers who are stuck at their lab benches all day long one of the big questions has always been how do you replicate experiments. If you read something interesting in a journal, how would you go out and do it yourself? So there's always that section in the research paper called 'methods' where they tell you which test tubes to use and really just how to put it together and how it all works. Well, what we have this week in the news section is a story about this new type of websites, based almost on the Wikipedia method, so encyclopaedias, where people have put their lab protocols online and you can go and edit them and people who go and say, well, you know, this particular reagent didn't work can make a little note on there and, essentially, edit them live. So we're calling it the Wikilab method. Nature 441, 678 (8 June 2006)

Anna Lacey: But how do you know that the people who are editing these protocols are genuine people who actually know what they're doing?

Alex Witze: Oh, you never know that. I mean, anyone can change them at any time. It really depends on the integrity of the academic community you could say and, presumably, if someone, such as myself, who didn't know lab protocols was going and messing around with them online, presumably somebody who was familiar with the practices would know right away that, no, this doesn't make sense. So it's sort of a group community effort.

Anna Lacey: But are people really going to want to share their scientific experiences? And, indeed, is it actually possible to share what is essentially tacit knowledge, actually sitting there and doing it in the lab?

Alex Witze: That's an excellent question and, of course, there are people who are working on protocols for very complex and difficult experiments with very high consequences and who may not want to share. Some people may be quite protective about how they do their particular measurement and how they got their exact results so the success of these websites will depend on how many people adopt them and in certain communities, the very competitive ones, they may not take off at all.

Chris Smith: With this week's news that was Nature's Alex Witze talking to Anna Lacey.This is the Nature Podcast from the 8th June edition of Nature with me, Chris Smith. If you'd like more information on any of the reports in this week's programme, they're all available on our website at http://www.nature.com/nature/podcast. And if you'd like to write to us about this or one of our previous podcasts, our email address is mailto:podcast@nature.com.And now to Australia and evidence of some of the Earth's earliest life, life that was flourishing 3.5 billion years ago. Abi Allwood from Macquarie University in Sydney has found a number of different types of layered rock formation called stromatolites, which were laid down by early microorganisms. The structures of these formations strongly suggest that they must the product of life and that life was already well established by the time they were formed. Nature 441, 714–718 (8 June 2006) ; Nature 441, 700–701 (8 June 2006)

Abi Allwood: What we've found is a fossilised reef that's built by some of the first living organisms on this planet, almost 3.5 billion years ago. That's not million, it's billion. To give some sense of how old that is, it's about 58 times older than the dinosaurs and almost as old as the Earth itself. And this is not just compelling evidence for life but I think with the diversity that you see there and the immediacy with which it arose suggests that life probably, in fact almost certainly, arose earlier than this and this is just one of the earliest remnants or oldest remnants that we have.

Chris Smith: Where did you find these things?

Abi Allwood: We found them in the Pilbara region of Western Australia. That's up in the northern part of the state of Western Australia.

Chris Smith: So what do they actually look like because presumably they've been changed by the passage of time quite considerably?

Abi Allwood: Remarkably, they haven't been that changed or that much changed as you'd expect and that's the amazing thing about these. What they actually look like as you walk along the outcrop of the rocks, you see the structures called stromatolites in cross sections. Stromatolites are sedimentary structures built by microbes in the sediment and in cross-section they'll look like chevron shapes or convex upward domes and so forth, with a laminated internal structure.

Chris Smith: How do we know that they're made by microorganisms if they're that old though?

Abi Allwood: That's the $64 million question. What I would say is that any one structure, even any one group of structures is not conclusive evidence of life in itself. The way I approached this was to look at a very large number of structures over a region and as I walked along the outcrops I began to notice that rather than just one type of structure there were actually several different distinct types and I set about documenting those and realised that they were distributed in patterns so that actually they look very similar to reefs, like the type of reef we're familiar with today. They're obviously not coral reefs. They're reefs entirely built by microorganisms.

Chris Smith: Why are they just in Australia? Is it geology that means that they've been preserved there and they were actually elsewhere on the world too or is it just there's something very special about this bit of Australia?

Abi Allwood: There is something special about this part of Australia in that some of the oldest rocks in the world, in fact the oldest well-preserved sedimentary rocks in the world occur there. There are some also in South Africa. In some ways with the Pilbara rocks, they're actually about the same age, the ones in South Africa. The succession there is a very similar age to the ones in Western Australia and there've also been putative bio signatures, different types found over there. And it's not to say that they weren't everywhere else in the world as well. It's just this is the one window that we have back into that period of time. These are the rocks that are preserved. That's all that remains.

Chris Smith: Macquarie University's Abi Allwood with the remains of some of Earth's earliest life.Now, we finish this week with a form of life that's not quite that old but it's every bit as exciting because Martin Sander from the University of Bonn has uncovered the first example of a dinosaur dwarf. Nature 441, 739–741 (8 June 2006)

Martin Sander: A few years ago somebody came to me and said there is a small dinosaur bone, would you like to get some histology samples from it and I said, yeah, well, I can always use some small dinosaurs, young dinosaurs. And then I sampled it and what happened is that these small dinosaurs were small dinosaurs but they were not young dinosaurs. They were dwarves.

Chris Smith: So, had previously no one discovered a dwarf dinosaur?

Martin Sander: Well, the idea of dwarf dinosaurs has been kicked around for a long time by especially the famous Hungarian palaeontologist, Nopcsa, 80 or 90 years ago but he couldn't prove it and only because of now that we study with a microscope and we can really prove how old something is in terms of its individual age, you know, if it's a youngster or a fully grown animal.

Chris Smith: So which dinosaur specifically was it that you found as a dwarf?

Martin Sander: It's a close relative to Brachiosaurus. That's that big thing with the high neck that's sort of like a dinosaurian giraffe. And those dinosaurs are very big.

Chris Smith: Do you think these are dwarves in the same way as we might describe humans as dwarves? In other words, it's a genetic change that leads to a whole group of individuals having that characteristic. Or do you think this is just an evolved group of dinosaurs that happened to be of diminutive stature?

Martin Sander: It's what's known as an island dwarf and what's happening is that if you introduce some species to an island either it goes extinct or it adapts to the decreased resources and then it decreases in body size.

Chris Smith: So where did these guys live that gave them this island dwarfing effect?

Martin Sander: First let's start where they were found. They were found in marine rocks in northern Germany and Germany, just like England, isn't really a terrific place to find dinosaurs because during dinosaur times our area here was all flooded and so we get great marine reptiles but we don't get great dinosaur finds. If we find dinosaur bones in marine rocks then that's very strange so you then have to go and find the land mass where they came from and what you do then is you go look at a palaeographic map and northern Germany, there was a basin of sea there that was surrounded by several large islands sort of the size of New Zealand.

Chris Smith: What is the giveaway then that they're dwarfed?

Martin Sander: Well, if you're lucky, and that works with most dinosaurs, you have growth marks like tree rings and one is laid down every year and just like in an old tree the bigger they get the more slowly they grow and the growth marks get very closely spaced. Then when you get very closely spaced growth marks then you know that was it. Growth slows down and so that's one clear indication that final size was reached.

Chris Smith: What sort of dates are we talking about here?

Martin Sander: That would be about 150 million years ago. It's sort of the heyday of these giant sauropod dinosaurs, you could say.

Chris Smith: And do you know how long this particular group of dwarves then persisted for or was this their end, they were only there for a short time and then disappeared?

Martin Sander: We don't know. I mean, we just have this one data point, basically, and there is a big section of rocks exposed but only in this one layer is where the dinosaur has come from. So they're all the same age, the same blink in time.

Chris Smith: So I guess you must be now quite eager to get back out there and see if there are more spanning a greater geological time?

Martin Sander: Right. Well, what I'm quite eager to do is really try to find out if Nopsca was right originally because, I mean, he had the idea after all and so if you see something small it really sticks out like a sore thumb. And so the next thing to do for me is really to see if the Romanian dinosaurs are dwarves as well.

Chris Smith: The University of Bonn's Martin Sander with the Jurassic sauropod equivalent of Homo florensiensis, the hobbit people.Well, that's it for this week. Thanks for listening. If you'd like to catch up with any of our previous podcasts or read the text transcript that accompanies this programme they can all be found at http://www.nature.com/podcast.Next time we'll be finding out how researchers are getting in a flap about butterflies and why cheap flights actually cost the earth. In the mean time, if you're still in the mood for some science, this week's edition of the Naked Scientist podcast takes a look at the oil industry and alternative energy technologies, including a way to make speed bumps generate electricity and how to turn the waste from a chocolate factory into fuel. That's the Naked Scientist podcast, which is freely available from http://www.the-scientist.com. Production this week was by Anna Lacey and Derek Thorne and I'm Chris Smith.The Nature podcast is sponsored by Bio-Rad, at the centre of scientific discovery for over 50 years and on the Web at http://www.discover.bio-rad.com.