Everybody’s talking about methane…

It actually started 16 years ago when Gerald R. Dickens and his colleagues published their paper on oceanic methane hydrate dissociation and the Palaeocene-Eocene Thermal Maximum (PETM). Their hypothesis that release of methane gas stored in oceanic sediments was the cause of the negative carbon-isotope excursion at the end of the Palaeocene and hence the trigger of the global warming recorded at the PETM, got scientists working on climate change and mass extinction around the world to suddenly set their old theories aside and focus on this new one.

Burning natural gas which consists of methane to 80% (Left) and a methane molecule (right).

Today, it seems, everybody’s talking about methane, CH4, this very potent greenhouse gas. From methane stored in clathrates underneath the ocean floor, or frozen by permafrost in the circum- Arctic or Antarctic tundra ( e.g. De Conti et al. 2012), to cattle or even farting dinosaurs during the Mesozoic, it poses a severe threat to life on Earth if released in large quantities. Hence, many scientific papers (see e.g. Payne et al. 2004 and references therein, and Ruhl et al. 2011) have argued that methane must have played a role in the end-Permian and end-Triassic mass extinctions, which are both associated with negative carbon-isotope excursions indicating input of light carbon (carbondioxide or methane from volcanoes or other sources).

My colleagues and I have studied the Triassic-Jurassic (T/J) boundary of the Denmark and compared that to a well known T/J boundary succession in England. In these two areas the carbon-isotope records exhibit three negative excursions separated by two intervals with more positive carbon-isotope values. What we have found is that the most profound floral changes on land and amongst organisms in the epicontinental sea that once covered these two areas, commenced within the first positive interval, i.e. between the first negative carbon-isotope peak and the second (most prominent) one. At the same level as the second negative carbon-isotope peak, which has been attributed to methane injection by e.g. Ruhl et al. 2011, the flora does not seem to be affected but is instead recovering, while organisms in the ocean continue to suffer. Hence our study suggests a more complex scenario…

You can read our paper (or just the abstract) or the press release.


Large herbivorous dinosaurs sustained Mesozoic greenhouse climate through flatulence?

In our society today we are very much aware of the effects of greenhouse gases on the climate. Global warming due to anthropogenic pollution has been discussed vigorously over the last decade. We spend enormous amounts of money on research and development of Carbon Capture and Storage, i.e. the possibilities of storing excess carbondioxide underground.

Geologists discuss the causes and effects massive release of carbondioxide or the four times more potent greenhouse gas methane possibly had on the climate and on life on Earth during the end-Permian and end-Triassic mass extinction events.

In a quest to find out what is normal and not normal when it comes to carbondioxide levels in the atmosphere, and the circulation of carbon on Earth, researchers have found out that our domestic cows produce some 50-100 million tonnes methane per year by gases formed in their guts.

Sheep are also environmental bad guys… 😉

Now a team of researchers lead by David Wilkinson have calculated how much methane may have been produced by large herbivorous dinosaurs, the so called sauropods including e.g. Apatosaurus, and their best estimates suggest 520 million tonnes of methane per year. A truly staggering amount as this equals the total combined methane emissions per year from all sources on Earth, i.e. from all animals and all human activities. 

     Sauropods probably had big guts containing lots of methane producing microbes!

The mean global temperature during the Mesozoic is estimated to have been 10 degrees Celsius warmer than today. Interestingly the Jurassic and Cretaceous periods are in general considered to have been periods of high diversity and productivity, both at sea and on land, despite the high levels of carbondioxide in the atmosphere.

So how come we fear carbondioxide and methane emissions today?

The key issue is probably time. Our planet; its interacting animals and plants, minerals and rocks, needs time to adapt to environmental changes. Fast injection of huge amounts of greenhouse gases to the atmosphere, whether from massive volcanism or from anthropogenic emissions, can shift climatic zones and cause major disruptions in ecosystems.

Perhaps the methane farts from the herbivorous dinosaur populations only sustained the greenhouse climate that was initiated at the end-Triassic?

Perhaps they didn’t really make things worse…just kept things normal?