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Q&A: Fungus or Algae? Using Mass Spec to Try to Settle Permian-Triassic Extinction Debate

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This story originally ran on Oct. 13.

By Tony Fong

SephtonPic.jpg

Name: Mark Sephton
Position: Professor, organic geochemistry and meteoritics, Imperial College, 2007 to present
Background: Reader, Imperial College, 2005 to present; lecturer, Open University, 2000 to 2005; post-doctoral fellow, Open University, 1998 to 2000; post-doctoral fellow, Netherlands Institute for Sea Research and University of Utrecht, 1996 to 1998

About 250 million years ago, about 90 percent of all species on earth disappeared in the greatest extinction event in the Earth's history.

During this period, called the Permian-Triassic extinction event, or more simply the "Great Dying," an organism called Reduviasporonites survived and covered the planet.

Reduviasporonites was originally believed to be a fungus that lived by eating dead wood in rotting forests. More recent geochemical data, however, suggested that the organism was algal in nature.

In a study published earlier this month in Geology, researchers from the UK, the US, and the Netherlands used gas chromatography-mass spectrometry to study the chemical signatures of Reduviasporonites and determined that it is not an algae but a fungus.

If so, that would suggest that rather than an extraterrestrial event, such as a meteorite impact, being the source of the "Great Dying," the mass extinction event would have resulted from a home-grown disaster such as the volcanic event known as the Siberian Traps.

ProteoMonitor spoke recently with Mark Sephton, a professor of organic geochemistry and meteoritics at Imperial College, about the research. Below is an edited version of the conversation.

What is the Permian-Triassic extinction event debate?

The Permian-Triassic is the biggest extinction in the geological record, so we need to try to understand it as best we can. One of our mechanisms by which we do that is to look for environmental proxies, organisms or chemical signatures that tell us about the conditions at the time.

One of these is the fungal remains, these little spores that we find that absolutely blossomed as they approached the Permian-Triassic event. The debate is: are they fungal or are they algal?

If they're fungal then they tell us that the world's forests declined and the fungus used this woody material, this food stock to absolutely proliferate and do extremely well. If they're algal, it just means we had very swampy conditions at the end of the Permian.

So it was very important as far as trying to understand the total ecosystem collapse that we work out what the origin of these remains were.

If they were fungal it would support the theory that there was some kind of global disaster?

Exactly … because we find the fungal spore on all continents and in all sorts of sedimentary records, so in all sorts of material that was laid down, so they're extremely widespread.

Whether they're algal or fungal, something changed at that time that made a particular organism do extremely well. And if they were algal it would be the onset of very swampy conditions. If they were fungi, it would mean that the food source was increased.

So we were looking at dead trees, and I think that the fungi are a better indicator of a global catastrophe than algae.

Would either one give you a better indication of the cause of an event?

I think the fungi are a better diagnostic simply because we believe they fed on trees. What's more, they're found everywhere and fungi do extremely well under low pH conditions. To get something that affected all continents, you really need a mechanism that involves the atmosphere, so we feel that this would be the Siberian Traps pumping these noxious gases into the atmosphere.

These gases spread throughout the globe, acidified the environment and degraded the ozone layer.

So the fungi would be a more specific environmental indicator than algae.

Was the mass spec technology something you've used before in your work or was it new to this particular study?

No, the mass specs I've used with colleagues to look at … meteorites. We've looked at the organic matter in meteorites. We've worked out the history of organic matter, what happened before it was incorporated into asteroids, what happened after it was incorporated, how asteroids evolve into planets, that sort of thing.

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The fungi have never been looked at in this way before. They're very small, and to get decent measurements, you need very sensitive equipment. It was natural that I would call on my colleagues who have the most sensitive mass spectrometers in the world to analyze these objects.

Can you briefly describe your research, especially the mass spec work?

It's a high sensitivity static mass spectrometer. It involved combusting the organic matter, carbon dioxide and nitrogen oxide. The isotopic ratios of the carbon dioxide are then measured. We measure the heavy carbons to light carbons … and that ratio tells us a number of things.

It tells us what sorts of reactions [took place]. For material from a meteorite, it tells us the source, because stuff from outside the earth is very enriched in the heavier carbon isotope.

For any non-biological reactions, it tells us about reaction mechanisms because carbon 12 is more reactive than carbon 13, and we can track the production of organic molecules.

And for fungi and similar organisms, we can recreate trophic relationships. That is, we can try to work out which organism lived on which food, because … you are what you eat, so you become slightly enriched in the heavier carbon and nitrogen isotopes.

It's a very useful tool to work out origins and materials, and relationships between organisms, and relationships between materials when you're looking at the chemical reactions. So there's a whole range of things you can do with this sort of technique.

What were some of the more novel or intriguing findings of your study?

The previous people had used geochemistry to try and understand these food source-consumer relationships, but what they've done is use carbon … and they looked at a potential food source, which was pollen and wood. But they took these materials from low down in the Permian, so from older rocks, and they took the fungal remains from younger times.

Now, that's not the best way to do things because this is a time of extreme background carbon isotope shifts. So you have to compare things, whether they're coeval, or from the same level.

And that's what we did. We took the food source from the same level as the organism and then we measured the bulk composition of the food source and compared it to the organism. What we found is that the organism is slightly enriched in carbon 13 as any organism that was eating something would be, but it was also enriched in nitrogen as well again as any organism that is eating some food stuff would be.

This is the first time that nitrogen has been used. It's very difficult to do nitrogen because there's less nitrogen in organisms than carbon. … That's why we have to use these high-sensitivity mass spectrometers.

Which was more important then, that you saw these traces of carbon 13, or these traces of nitrogen?

I think both. Both observations are important and are consistent with the fungal lifestyle. The nitrogen is important because it's new. It's another diagnostic piece of information that we didn't have before. And in a controversial area, you need as many pieces of diagnostic information as you can get.

Now, we can talk about whether we're 100 percent certain. That's another matter. … But you have to go with the fungal [theory]. You'd be stretching yourself to try to fit this data into an algal organism.

Your study doesn't say outright that it supports any evidence of fungal affinity. It says only that you can't dismiss evidence of such affinity.

To some extent, that's just a British euphemism.

The arguments that were leveled against the fungi have been proved not to be water-tight. Effectively, we're back to the situation we were at before with the fungi being the most likely interpretation, and all of the data is consistent with fungi.

The data is less consistent with algae. You never say you're 100 percent certain, but if I had to bet my house on it, I would choose the fungal interpretation.

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What effect do you think this will have, or what effect has it had on the Permian-Triassic debate?

It's surprised me how over the last few years, how quickly the idea that the fungal remains could be algal has been adopted. I never thought the data was that convincing, and it's nice to see it being brought back [into] the debate.

It's clearly an organism that's responding to a change in environmental conditions. We don't see this sort of fungal spike anywhere else in the geological record, so it's important that we try to understand its origin, its lifestyle, and its relationships via extinction because there clearly is one.

It's a remarkable event, and it's tied with all sorts of other geochemical signals that also go crazy at the end of the Permian as well. I think its demise as an environmental indicator was overstated. So it's nice to have it back reinstated where it belongs.

Have you received any reaction to the study so far?

We've had lots of media interest. Scientifically, no one's questioned the work. We've had some scientists who've asked for comments. They've been very supportive. They said we did a really good job. It went through the review [process] without corrections, so the reviewers completely accepted what we were saying, and I think it's a good piece of work, so people seem to appreciate that as well.

Did you see any evidence of meteorite or extraterrestrial material?

No. In fact, the fungi are quite an important indicator … because the fungal remains are present in the environment before the end of the Permian, before the extinction happens.

[There's this] incredible proliferation, this incredible abundance of these at the end of the Permian that's unusual. And they do slowly increase as you approach the end of the Permian. If you were thinking about an extraterrestrial mechanism to the extinction event, you couldn't have the world getting ready for that event to happen unless you'd think these organisms have some sort of psychological trauma because they knew the meteorite was coming.

It's a big blow to people who like to give the impact hypothesis a run at the end of the Permian because the ecosystem is clearly suffering before the event, and therefore it looks like a homegrown mass extinction cause.

How else are you using these mass specs in your lab? What else are you exploring?

The mass spec data is generated by Alexander Verchovsky whom I've worked with for a while. He's now at a different institute than me. We have one particular mass spec that we use for molecular characterization. We use pyrolysis and you see that data in the paper.

We take big molecules and we fragment them into smaller molecules that we can analyze, and by looking at the smaller units, we can then use our brains to reconstitute the Permian material, and this is how we understand what the origin of the organism might be, because we look for specific chemical signatures … that tell us what it was in life.

Are you looking for chemical signatures or biological signatures?

They're chemical but all of the chemicals that you find in geological records usually were once biological, so we're looking at molecular fossils. People who are used to seeing fossils that are shells or skeletons, well, you can have molecules that are fossils, as well.

For instance, certain organisms which lived in specific environments, their organic matter are varied and preserved, and when we see their molecules, we can say, 'This was a particular algae or a particular tree that lived in a particular environment,' so we know that that time in geological history was marked by such environmental conditions.

Can you describe any follow-up work you're doing to the Geology study?

We're going to look more at the chemical remains, looking at different sections that may have better preserved molecular fossils. But we're also going to be looking at the morphological similarities between the ancient fungi and modern day fungi.

Maybe by comparing the shapes, and structures, and forms of ancient fungi with modern fungi, we can try and really tease out the secrets of these Permian fungi's lifestyle.

It'll tell us how they lived, whether they were single species, multiple species, what was their predominant food source, whether they lived predominantly in the soil or on trees, those sorts of things.

That is work that is done by my co-author, Hank Visscher. He's the morphology expert. We sort of bounce among different specialties. Some of our papers concentrate on chemical signatures, some concentrate on morphological indicators.

Are you taking a more shotgun approach to your work, or are you taking a more targeted approach?

We're always looking for biomarkers of fungi in the geological record around the Permian. … We're always open-minded and we're always looking for diagnostic information.

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