Did dinosaur farts cause Mesozoic global warming?

[Arete]

Off the back of the wind farm thread comes the dino farts warming hypothesis! At least this one might be amusing.

 

The argument is that as livestock produced methane is a major contributor to greenhouse gases today, so one can speculate that sauropods would have contributed significantly to atmospheric methane back in the Mesozoic - which was known to have been warmer than today. A recent Current Biology paper gives some back of the envelope calculations and finds out that if sauropod farts may well have been a significant greenhouse gas source:

 

 

http://www.cell.com/current-biology/fulltext/S0960-9822%2812%2900329-6

 

"Mesozoic sauropods, like many modern herbivores, are likely to have hosted microbial methanogenic symbionts for the fermentative digestion of their plant food [1]. Today methane from livestock is a significant component of the global methane budget [2]. Sauropod methane emission would probably also have been considerable. Here, we use a simple quantitative approach to estimate the magnitude of such methane production and show that the production of the ‘greenhouse’ gas methane by sauropods could have been an important factor in warm Mesozoic climates...

 

As an illustrative example, we consider the sauropod biomass density of 200,000 kg/km² to consist of ten 20,000 kg sauropods; this is a conservative estimate of the adult mass of the medium sized sauropod Apatosaurus louise, colloquially known as ‘Brontosaurus’. For this, the allometric relation gives methane emission of 2675 litres per day for one animal, equivalent to about 1.9 kg per day under the standard temperature and pressure conditions assumed in [7]. For a density of ten adults per km², assuming, for comparability, modern day and year lengths (the Mesozoic day was slightly shorter), we get 6.9 tonnes/km² of methane per year methane emissions. Scaling up, assuming a global vegetated area of 75 x 10⁶ km² (equivalent to half the total land area), gives global methane production from sauropods of 520 Tg (520 million tonnes). This is comparable to the total modern-day methane emission (Figure 1) [2]."

 

"Estimated sauropod methane production compared to total modern (both natural and anthropogenic), global pre-industrial and estimated modern methane production from ruminants. Even reducing our estimate by half still predicts a major role for sauropod methane in the Mesozoic."

[CaptainPanic]

The earth's land mass has been pretty constant throughout the ages.

Therefore, there were an equal amount of plants growing in the dino era compared to modern times.

Therefore, there should have been an equal consumption of plant material, either by large, small, or microscopic plant eaters.

Therefore, I don't see why there should ever be any difference in methane production.

 

The study pretty much suggests that cows and dinos fart more in comparison to other animals, and I don't see why. Why wouldn't elephants, or rabbits, or giant sloths or any other plant eater fart just as much?

 

Also, I admit I didn't read the whole paper.

[Arete]

The earth's land mass has been pretty constant throughout the ages.

Therefore, there were an equal amount of plants growing in the dino era compared to modern times.

Therefore, there should have been an equal consumption of plant material, either by large, small, or microscopic plant eaters.

Therefore, I don't see why there should ever be any difference in methane production.

 

The study pretty much suggests that cows and dinos fart more in comparison to other animals, and I don't see why. Why wouldn't elephants, or rabbits, or giant sloths or any other plant eater fart just as much?

 

Also, I admit I didn't read the whole paper.

 

 

1) Biomass and therefore methane budgets are not constant over time - biomass is not uniformly distributed over land mass, so there's no reason to expect it to be uniformly distributed over time and if fact it most likely hasn't been.

 

http://www.sciencema...5741/1714.short

 

2) Ruminants produce significantly more methane than non-ruminants due to the fermentation process by which they digest their food. The paper makes the rather speculative leap that saurpods also digest their food via a fermentation method - but if they did, then they might have a point.

 

http://www.google.co...SRwF8fA&cad=rja

Edited May 8, 2012 by Arete

[iNow]

No, dinosaurs did not fart themselves to death. Here's what the paper says:

 

 

Take together, our calculations suggest that sauropod dinosaurs could potentially have played a significant role in influencing climate through their methane emissions. Even if our 520 Tg estimate is overstated by a factor of 2, it suggests that global methane emission from Mesozoic sauropods alone was capable of sustaining an atmospheric methane mixing ratio of 1 to 2 ppm. Equally, our estimate may be understated by a similar factor, (i.e. possibly supporting 4 ppm methane). In the warm wet Mesozoic world, wetlands, forest fires, and leaking gasfields may have added around another 4 ppm methane to the air. Thus, a Mesozoic methane mixing ratio of 6–8 ppm seems very plausible.

 

The Mesozoic trend to sauropod gigantism led to the evolution of immense microbial vats unequalled in modern land animals. Methane was probably important in Mesozoic greenhouse warming. Our simple proof-of-concept model suggests greenhouse warming by sauropod megaherbivores could have been significant in sustaining warm climates. Although dinosaurs are unique in the large body sizes they achieved, there may have been other occasions in the past where animal-produced methane contributed substantially to global environmental gas composition: for example, it has been speculated that the extinction of megafauna coincident with human colonisation of the Americas may be related to a reduction of atmospheric methane levels.

 

Their contributions may have been substantial, but they were stable. Yes, there was likely some warming from it. No, it's not likely what killed them.

[Arete]

No, dinosaurs did not fart themselves to death.

 

I'm not sure anyone was implying that sauropod methane caused an extinction event...?

[iNow]

Consider it preemptive, then. That's all I've been hearing from the Faux News camp.

[Dekan]

The Earth plants has plants living on it, also animals. But aren't these just different forms of the same mass of living substance?

 

This living substance must stay the same in mass, all the time. Because surely the Earth can only hold a certain mass of living tissue. This tissue may be built into different body shapes. Shapes such as microbes, or amoebae, plants, worms, insects, fish, birds - or dinosaurs.

 

But altering individual shapes, can't alter the total mass of biological material. Even in the Mesozoic.

 

Because all this material worked the same way - whether it was incorporated in an apatosaurus or the giant ferns that it ate. So - no global warming from dinosaurs.

 

(Global changes really get zipping when humans invent non-biological machines such as steam engines and coal-fired power stations. These really shake up the environment, and isn't every science-minded person loving it?)

[zapatos]

This living substance must stay the same in mass, all the time.

So you believe that the KT extinction had no impact on the amount of living substance?

Or that the mass of living things is the same now as it was 3.8 billion years ago?

[CaptainPanic]

I'll try again, since my point wasn't fully understood.

 

We're talking about the following (overall) reaction:

 

Plants --> Methane

 

My problem is that the article concludes:

 

Animals --> Methane, or specifically (quoted): Methane (litres per day) = 0.18 (body mass in kg)^0.97

 

... which is rubbish.

 

It's like saying you can make cars from factories. No, cars are made of steel and plastics. So, you need to know how much steel is being produced. Likewise, it is far more important to talk about the growth of plants, than the estimated total mass of brontosaurs on a square kilometer.

 

2) Ruminants produce significantly more methane than non-ruminants due to the fermentation process by which they digest their food. The paper makes the rather speculative leap that saurpods also digest their food via a fermentation method - but if they did, then they might have a point.

 

Exactly.

In addition it would be important, as Arete just pointed out, to know what kind of "factories" (animals) you have. If you know the world's total steel production, you cannot estimate the number of cars produced - although it is important. You also need to know what kind of factories there are.

 

The article says that in the dino age, there was a lot of sauropod meat walking around. So, there must have been a lot of methane. But they completely fail to address the type of digestive system of the sauropods.

[Arete]

I'll try again, since my point wasn't fully understood.

 

We're talking about the following (overall) reaction:

 

Plants --> Methane

 

My problem is that the article concludes:

 

Animals --> Methane, or specifically (quoted): Methane (litres per day) = 0.18 (body mass in kg)^0.97

 

... which is rubbish.

 

Plants don't release methane. The conversion of plant matter to methane requires anaerobic decomposition - and if the major contributor to anaerobic decomposition of organic materials is an animal, it is the abundance and contribution of the animals that is important.

 

E.g. If we wanted to work out the contribution of methane to the atmosphere of a dairy farm it would not be sensible to go out and determine the biomass of grass on the farm. It wouldn't tell us anything about the contribution of methane from the farm at all as the grass itself is not contributing methane to the atmosphere. If we work out that the fermentation of the grass by the cattle is the major contributor, how much methane per cow per day is released and how many cows, we will. It is only by analyzing the cow data you'd determine the methane contribution of the farm.

[CaptainPanic]

Plants don't release methane. The conversion of plant matter to methane requires anaerobic decomposition - and if the major contributor to anaerobic decomposition of organic materials is an animal, it is the abundance and contribution of the animals that is important.

 

E.g. If we wanted to work out the contribution of methane to the atmosphere of a dairy farm it would not be sensible to go out and determine the biomass of grass on the farm. It wouldn't tell us anything about the contribution of methane from the farm at all as the grass itself is not contributing methane to the atmosphere. If we work out that the fermentation of the grass by the cattle is the major contributor, how much methane per cow per day is released and how many cows, we will. It is only by analyzing the cow data you'd determine the methane contribution of the farm.

And likewise, it also wouldn't make sense going around counting all types of farms, without knowing which kinds of animals live in that farm, and then draw a conclusion about the amount of methane produced. As you pointed out, all animals are equal, but not when it comes to flatulence. So, it matters how many cows there are, not how many farms.

 

If you want to make a mass balance (and we do), you have to realize that every carbon atom in methane that is formed in the belly of a beast comes from a plant. A brontosaur is only a chemical factory on legs, like every animal btw. If you want to know what comes out the back end, you need to start making a balance. And that means you need to know what goes in at the front. If you do not take that into account, you cannot get a balance. I'm sorry, but that's just how all engineers calculate what happens in a process (and yes, that last sentence is an argument from authority, which is actually a fallacy).

 

If you want to make an assumption of the amount of methane produced (from plants) in the bellies of brontosaurs, you'd better start off knowing how much plants were being eaten. Then make an assumption on the percentage of the plants being converted to methane. And then you get a decent estimate.

 

I have a problem with the entire method in that paper... not so much with the results, which might coincidentally be correct. But that would be luck, not science.

[Arete]

If you want to know what comes out the back end, you need to start making a balance. And that means you need to know what goes in at the front.

 

If all you're interested in is what comes out the back end and you can directly measure that [as they can for extant ruminants like cows], why do you need to know what goes in the front?

[JohnB]

If all you're interested in is what comes out the back end and you can directly measure that

 

Since dinos died out some 65 million years ago, how do you propose to "directly measure" their methane production?

 

I would also point out that one of their basic assumptions is quite possibly incorrect.

 

Unlike most modern browsers which are restricted to low growing vegetation, sauropods could access high tree foliage. This ability to access high as well as low browse because of their large body mass may partly explain why we infer sauropod methane emissions to have been much greater than those of modern-day ruminants which produce 50-100 Tg per year.

 

The last I heard the jury was still out as to the flexibility of the saurapod neck. The most recent views I'm aware of are that unlike earlier thought (and depictions in movies like Jurassic Park) the larger saurapods did not raise their heads much at all, but browsed on lower fodder by sweeping their head and neck from side to side. The head stayed roughly at shoulder height and while this is still perhaps 20 feet or so is not enough for "high tree foliage".

 

Apparently it's a matter of blood pressure.

 

But I don't think that the article was intended to be taken seriously.

[CaptainPanic]

If all you're interested in is what comes out the back end and you can directly measure that [as they can for extant ruminants like cows], why do you need to know what goes in the front?

You do that in order to avoid making a prediction for the back-end-production which is not possible because there is simply too little plant material. A balance avoids that problem. We have no direct measurements. We're talking about predictions and models here.

 

The rest I already explained above.

[Xelloss]

I don't think it would be necessary to make the calculations that complicated; if we can figure out how much of the methane was emitted from their manure then we have a good enough estimate. The only problem is, is that we don't really know how much manure a typical brontosaurus would have produced. Now if we can find a creature with its manure fossilized, it would make the task a lot easier. Though it is unlikely that such a thing would be fossilized after millions of years...

 

Alternatively, the above calculations could be done if the stomach was somehow fossilized; then we would know how much the things actually ate (or even what they could have possibly eaten).

Edited June 4, 2012 by Xelloss

[Royston]

Though it is unlikely that such a thing would be fossilized after millions of years...

 

I actually have a coprolite, though I'm not sure what pooped it out. I'm sure there are plenty of examples that you could use to ascertain the average amount of dung produced by a large herbivore. It might be worth pointing out that dung was also a source of food for smaller dinosaurs. Here's an example of a sauropod coprolite...

 

Edited June 4, 2012 by Royston