Planet Earth Online - Friendly Fires

28 November 2010

Interview with

Andrew Scott, Royal Holloway University of London

Diana -   In July this year, five devastated a Surrey beauty spot.  Fire fighters from three counties tackled the blaze on Frensham Common but 86 acres of heathland were reduced to a scene of blackened devastation.  It may take up to five years for the affected land to recover, but not everyone views fire as a destructive force.  Planet Earth podcast presenter Sue Nelson joined Paleobotanist Andrew Scott from the Royal Holloway University of London on the charcoaled remains of the blaze, to find out how fire can also bring the past to life...

Andrew -   You can notice as we're walking, your feet beginning to crunch although it's a bit damp today.  Lots and lots of different sizes of charcoal here.

Sue -   Now you've just put a trowel into the ground there.  It almost looks like the sort of beautiful dark and composty peat that you might buy from a garden centre.

Dry CharcoalAndrew -   Yeah and so, you'd probably think, "This is terrible stuff."  But in fact, this is preserving the plant material as charcoal.  What I consider fire as, is that if you like a preservational mechanism for fossil plants because in many cases, this charcoal now is the cell walls have been converted to nearly pure carbon, and that material can get buried and survive for millions of years.  Not only that.  The anatomy of the plants are still preserved in the charcoal.

Sue -   It's hard to see how anything could be preserved in what looks like the remains of a fire grate.

Andrew -   Yes, I know.  It's sort of almost counter intuitive, isn't it?  If you take this back, and we will, we'll take it back to the lab and look under the microscope.  You'll see that all of the different tissues of the plants are preserved.  I'll collect a bag of the material so that you can actually see that I'm telling you the truth.  One of the problems of course is that this material, as you commented, who would think of collecting that stuff?  And so, one of the things we have to do is persuade people that this is incredible material.  It tells us not only that there was a fire here, but we can tell what was being burned.

...

Sue -   A short drive away and we're now in Andrew's offices.  We've brought some of the charcoal with us, and you've got a microscope here.

Andrew -   So I'm just going to take some of the sample out.

Sue -   A spoonful there.  A bit like spooning out some tea, isn't it?

Andrew -   Sometimes they're often called fossil tea leaves, I think for some people anyway.

Sue -   Oh my goodness!  You can see textures, almost like tiny seeds.

Andrew -   This is rather wet and clumped together, but one that I collected earlier and dried out, I think if I show you this under the microscope...

Sue -   You're using a very fine tipped paintbrush now to sort through the powdered charcoal.

Andrew -   Yeah.  I'll just turn it around.

Sue -   That looks like a clove in that it's got a little stick and a roundish head with two little pins-like protrusions from the top.

Andrew -   That's a charred heather flower.

Sue -   Gosh!

Andrew -   So let me find you another bit of the heather.  This is another one of the flowers that's actually opened up.

Sue - That almost looks like a miniature black rose bud.

Andrew -   Yeah, it's amazing.

Sue -   So the charcoal is a treasure trove as far as you're concerned, but why is it important to examine the remains of these plants?

Andrew -   Our thoughts about charcoalified flowers started with the discovery by Else Marie Friis and colleagues in Sweden of some cretaceous material, in which they discovered these tiny little flowers preserved as charcoal.  This was a period when flowering plants first started.  We know that many of the flowering plants were small, shrubby, weedy forms, and they survive well in disturbed habitats.  But the other thing to know is of course, fire is a major disturbance and if you've got regular fires, then these weedy plants can do very well.  They come back very quickly.  If the fire return interval is quick enough, you prevent any trees growing.  But the question is, why in the cretaceous and why is it so interesting?  We know from experiments that if you have changes in atmospheric oxygen, that can affect fire.  Because if atmospheric oxygen falls below 15% you don't get fire, it gets put out.  If you have much above the present level, you can begin to burn wetter and wetter plants.  So the idea we had was that if you look in ever wet environments, if you have increasing amounts of charcoal, it may indicate that oxygen levels are increasing.  So we've just published our research which tries to use this as a proxy of atmospheric oxygen through time.  Now it turns out that the cretaceous, this period when flowering plants first got going, was a time of high oxygen.  So we believe that there were many more fires that could burn.  They promoted, if you like, the spread and diversification of early flowering plants.

Diana -   Andrew Scott from Royal Holloway University of London, talking to Planet Earth podcast presenter, Sue Nelson.

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