Archive for the ‘Paleoclimatology’ Category

With Such Volcanoes, WHO NEEDS ASTEROIDS?

June 21, 2015

I have long been of the persuasion that the asteroid did not extinguish the dinosaurs: it was too puny. I did not see how a big explosion could have extinguished giant life forms such as the Mosasaurs, who lived in the sea, on the other side of the planet.

Mosasaurs are central to this story: the name, Moselle Lizard, comes from the Moselle, a famous river which flows through the town of Maastricht, next to which the first Mosasaurs were found. In 1794, French revolutionary forces took control of the fossils (against 600 bottles of wine), and brought them to Paris Museum d’Histoire Naturelle for state of the art analysis. Cuvier, by 1808, had formally concluded that  le Grand Animal fossile de Maëstricht confirmed the evolutionary theory of his great rival Lamarck.

Pinatubo Warming Up, June 12, 1991

Pinatubo Warming Up, June 12, 1991

[The main Pinatubo eruption was three days later, and was obscured by ash and clouds all over; Pinatubo had strong global effects on world temperature; However, by geological standards, Pinatubo was tiny: 10 cubic kilometer of ejecta, 1% of Tambora in 1815; the Deccan Traps LIP was of the order of millions of cubic kilometers of ejecta.]

The age of the Mosasaurs accordingly became known as the Maastrichtian. Characterized by Mosasaurs, it covers the last six million years of the Cretaceous. And a tremendous discovery, the one I had been expecting all along was just made: the Maastrichtian was a time of colossal transitions. So much for the asteroid impact.

There was an obvious culprit for the extinction at the end of the Cretaceous: the Earth Core Eruption of the Deccan Traps. OK, “Earth Core Eruption” is my own semantics, and the theory behind it is not proven. The official term is Large Igneous Province (LIP).

Climate Apocalypse Well Before The Asteroid:

A decade long project in Northeastern China has drilled sediments as ancient as 100 million years ago. It is bringing results I expected, but even more so.

For millions of years before an asteroid struck the planet 66 million years ago, Earth’s climate was already in turmoil.

It has long been known, from ocean floor sediments, that the climate was unstable at the end of the Cretaceous period. Findings from deep drilling in the Songliao Basin show that the climate swings on land were far more drastic, than anyone expected. Average annual temperatures fluctuated up and down by as much as 20°Celsius over tens of thousands of years—a geological eyeblink. “It certainly wasn’t a good time for the dinosaurs,” says Robert Spicer, a paleoclimatologist at the Open University (Milton Keynes, U.K).

Sediments were piling up in the ancient lakebed in northeastern China at a much faster rate than in the ocean. This provides with a much finer chronology.

Shallow seas had contributed to warm and moisten the Earth so much in the age of dinosaurs (before, during and after the Jurassic). Evolving plate tectonic eliminated those during the last few million years of the Cretaceous. That snuffed out many species and hobbled others.

The Songliao Basin was a gigantic lake for 80 million years. During the Cretaceous, it covered 260,000 square kilometers, as much as the area of New Zealand (a micro-continent in my book). The lakebed’s sediments “provide a unique record of what the land environment was like during this turbulent time,” (Page Chamberlain, a paleoclimatologist at Stanford University, a principal investigator of the Songliao International Continental Scientific Drilling Project).

The drilling team, led by Wang from Beijing University, has gone 2.6 kilometers down. Analyzing oxygen and carbon isotope ratios in the sediments the seesawing temperatures during the last 6 million years of the Cretaceous, the Maastrichtian.

High latitude, and the pace of sediment deposit, ten times what it is in the ocean, gives a very fine record.

The sediments reveal not only astounding temperature swings, but also their likely cause.

Two major Maastrichtian warming events captured in the Songliao cores—68 million years ago and 66.3 million years ago -thus, BEFORE the asteroid impact- coincide with massive eruptions of the Deccan Traps, the Large Igneous Province in India.

Carbon isotope studies show that second warming event was characterized by a rapid doubling in atmospheric carbon dioxide. “This was the time when the bulk of Deccan eruptions occurred, which presumably released a massive amount of carbon dioxide,” says Zhang Laiming (China University of Geosciences).

Differently from an asteroid impacts, large volcanic eruptions are characterized with nasty fluctuating gases and temperatures. We know this from Iceland’s Laki eruption in 1783. Europeans found themselves experiencing various gases, some floating by the ground like colored fog, and tremendous variations of temperatures: hot sometimes during winter, cold in summer.

A volcanic eruption can release sulfates, which can bring considerable cooling, for the years they can stay aloft (around five years). Pinatubo cooled the entire planet by nearly one degree Celsius, thanks to this.

However, a volcanic eruption is greatly propelled by CO2, and that can warm up the cilmate for millennia. The combination is a strong whipping around, between cold and heat.

Now in parallel essay, I will make clear that dinosaurs were ill equipped for such fluctuations.

The intense greenhouse effect caused by CO2 from the Deccan Traps drove average temperatures to about 22.3°C. This compares with only 5°C at Songliao today.

The warming was interrupted just after the K-Pg boundary by a brief cooling episode. The team attributes to dust, soot, and aerosols from the Yucatán asteroid impact. However, I would point out that this is just a theory. In 1809 an unknown volcano exploded in the south hemisphere (as determined recently by ice cores). That was followed in 1815 by the explosion of Indonesia’s Tambora. The result was the coldest decade in more than a millennium (and may well have cost Napoleon’s army tremendous losses in Russia, as the 1812 winter was the coldest on record there).

As temperatures convulsed (and probably acidity in the oceans), ecosystems changed. The Songliao sediments trapped spores, pollen, algae, and ostracods (“seed shrimp“).

To my complete non-surprise, many of the species typical of the Paleocene —the geological epoch following the Cretaceous— appeared several million years before the K-Pg boundary (the first period of the Paleocene is called the Paleogene, Pg). Turnovers in the biota, Wang says, “had already been under way when the asteroid struck.”

Dinosaurs were already on their way out. The number of nonavian dinosaur species seem to have shrunk by half in the last 10 million years of the Cretaceous, with the biggest losses during the Maastrichtian (although according to a French geologist, there may have been more than 1,000 dinosaur species at the end). The Chicxulub impact was, Wang says, “the straw that broke the camel’s back.” Put another way, Spicer says, “if the asteroid came in on a less stressed system, the effects would not have been so severe.”

Well? Now the asteroid is reduced to a straw. We don’t need the asteroid. Straws sometimes change history. If Grouchy had not got lost at Waterloo, the French would have won. But not in the case of dinosaurs and mosasaurs, and pterosaurs, plesiosaurs, and maybe ammonites. Straw, or not straw, they were all condemned.

I have a general reasoning, the one I used to explain the “disappearance”, or, more exactly, dilution, of the Neanderthals, to explain this. It implies that large animals tend to disappear more readily. All the more those who did not control their temperatures well. Competition from mammals and avian dinosaurs condemned the dinosaurs.

Yet, there are lessons for today; the cataclysm we are visiting on the biosphere is orders of magnitudes more violent than anything which happened during the Maastrichtian. Even the dinosaurs were not dumb enough to organize their own doom.

Patrice Ayme’