A story making the rounds is creating headlines such as the one in the ever credulous Arizona Daily Star: “Flatulent dinosaurs helped warm Earth, study says.” British researchers posit that the flatulence of herbivorous dinosaurs produced so much methane that it warmed the climate. The paper, published in Current Biology is summarized by the authors as follows:

Mesozoic sauropods, like many modern herbivores, are likely to have hosted microbial methanogenic symbionts for the fermentative digestion of their plant food. Today methane from livestock is a significant component of the global methane budget. 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.

If you read the story (full text here) you will find that the contention depends on many assumptions and rather extravagant extrapolation. The gassiest dinosaurs were the Sauropods which became abundant during the Jurassic Period about 150 million years ago. Global temperatures are estimated to have been 18 F warmer than today, but that warmth began in the preceding Triassic Period about 250 million years ago. There seems to be a timing problem. Also, the researchers estimate that the amount of methane produced by dinosaurs was similar to the amount produced today by livestock farming and industry, so why aren’t we warmer?

At the end of the paper, the researchers note as an attempted justification for their speculation:

 ”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 colonization of the Americas may be related to a reduction of atmospheric methane levels.”

That references a 2010 paper in which the researchers estimated the amount of methane produced by mammoths and other large herbivores. They speculate that the arrival of humans in North America and the subsequent disappearance of these animals reduced methane emissions and led to an abrupt cooling period, the Younger Dryas, about 12,800 years ago.

At the end of the Younger Dryas, the global temperatures and atmospheric methane both rose rapidly. So where did the methane come from since those flatulent mammoths were no more? The mammoth fart theory fails to explain previous similar abrupt cooling and warming in the Older Dryas period and the Oldest Dryas period, nor a subsequent similar event about 8,200 years ago.

Both of these papers present interesting stories, but they both fail upon close inspection. Still, science is speculative and the stories make headlines and get the authors published.

See also:

Arizona Geological History Chapter 5: Jurassic Time

Ice Ages and Glacial Epochs

Research Review 3 Climate cycles and a Mammoth Mystery

Mammoths, mastodons, saber-toothed cats, glyptodonts, and other great beasts roamed the land of North America, Europe, and Asia, until something happened about 12,000 years ago. Just what that something was, is subject to great debate. We will focus on the case in North America.   

Hypotheses attempting to explain the extinctions include: The mammoth hunters “is wot done it”, disease, normal climate change at the end of the glacial epoch, and abrupt climate change caused by a big flood or a comet strike.   

Here is what we do know. Humans (of the Clovis Culture) entered North America at least 13,500 years ago when abundant megafauna inhabited the land. The planet was warming up from the last glacial epoch and had reached temperatures similar to today. Between about 12,900 and 11,500 years ago there was an abrupt cooling episode called the Younger Dryas (after a small Arctic flower), during which global temperatures plunged, in a matter of decades, from temperate climes to near glacial conditions. It stayed cold for about 1,400 years then rapidly warmed again. During that time, most of the megafauna became extinct. Evidence of the human Clovis culture also disappeared.   

That point in time about 12,000 years ago, the end of the Pleistocene epoch, is marked in many places with a “black mat” of rich organic material. Below the mat are abundant fossils of megafauna and artifacts of the Clovis culture. No such fossils and few, if any, Clovis artifacts are reported above the black mat.   

A study of the black mat at 50 Clovis sites in North America found a “discrete layer with … magnetic grains with iridium, magnetic microspherules, charcoal, soot, carbon spherules, glass-like carbon containing nanodiamonds, and fullerenes with ET helium, all of which are evidence for an ET impact and associated biomass burning at 12.9 ka.”   

Let’s examine the hypotheses: (more…)

The ethnobotany of Mesquite trees is extensive. The trees provide food, medicine, beverages, glue, hair dye, firewood, and furniture. Mesquites coevolved with large herbivores such as mammoths, mastodons, and ground sloths, which ate the pods and dispersed them widely. When these Pleistocene animals became extinct, mesquites retreated to flood plains and washes where water and weathering scarified the seeds and aided germination. The introduction of cattle helped to expand the range of mesquites once again.

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