The Queen of the Sciences solves the mystery of the dinosaurs’ demise

Medieval academics called theology (or alternatively philosophy) the “Queen of the Sciences” because they saw it as the capstone of all higher learning. Carl Friedrich Gauss used this term to describe Mathematics. I would reserve this term for Paleontology for the way it integrates physics, chemistry, geology, biology and of course mathematics, while revealing deep truths about the history of the planet that gave us birth. Check out this amazing paper on evidence for the global “impact winter” that followed the arrival of the asteroid that killed the dinosaurs 66 million years ago. http://www.pnas.org/content/early/2014/05/08/1319253111

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The authors have reconstructed changes in sea surface temperature and deposition of particles, from tsunamis and the fall of dust from the atmosphere, over a time scale of a century or less immediately following the impact.  They worked in a site along what is now the Brazos River in Texas, but which 66 million years ago (Ma) would have been offshore at a depth of a 75-200 m.  This location was about 1000 km from where a 10-km asteroid collided with the earth. The impact site, which left an enormous crater, is where the northern edge of the Yucatan Peninsula now seems to pinch off the Gulf of Mexico. At the time of the impact it was also underwater.

At the Brazos river site is a rock stratum that dates to 66 Ma. Like other strata of this age all over the world, it has a narrow band of minerals with high concentrations of iridium (an element rare on earth but common in asteroids), shocked quartz, and other signatures of an impact big enough to have ejected quantities of material in the atmosphere to be carried and deposited around the globe.  The realization that there was such a large impact has led to a hypothesis about how the impact affected living things. In a nutshell, the impact caused a massive tsunami, a fireball that killed a lot of organisms outright, and then a cloud of atmospheric dust so thick and so persistent that it blocked out the sun’s light, shut off photosynthesis worldwide, and therefore deprived living things of energy for a period of time ranging from decades to centuries.  Thus, by plunging the whole earth into dark and cold, the impact led to the extinction not only of the dinosaurs but also of a large number of other terrestrial and marine species.

What was lacking was direct forensic evidence of this “impact winter.”  The Brazos river site provides it.

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The site is special because it is close enough to have experienced a direct hit from the tsunami that the asteroid caused.  Just below the iridium layer is a layer of larger particles whose size is consistent with what would be laid down by tsunami waves.  Above the tsunami deposits are successive layers of smaller and smaller particles (including those high in iridium). The progressive decline in particle size makes sense because finer particles would take longer to settle in water.  Knowing how fast particles of different sizes settle gives a way of estimating that the layers took a hundred years or so to accumulate. The researchers could also take the temperature of the sea (and hence the earth) as the particles settled by examining the fossils of tiny sea creatures (foraminifera and dinoflagellates) that were found among other particles. Like their modern relatives, these creatures produced a particular lipid in amounts that  correlated with the temperature of the water.  This so-called paleothermometer reveals downward spikes in sea-surface temperature of 6-7 °C, which could only be explained by the sun’s radiation being blocked. The temperature drops happen just before the iridium-containing particles settled, which suggests that they were in the dust clouds that had blocked the sun.  The temperature drops are short in duration, presumably because the dust got rained out of the sky over the ensuing decades.  Again, this overall sequence of events, all of which left signatures in rocks found today, spanned a hundred years or less.

That we can understand events spanning a century at a remove of 66 million years is a feat of human ingenuity that I find simply astonishing.  Philosophy is the queen of the sciences?  I think not. My vote is with paleontology.

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Hortus deliclarum (Garden of Delights), 12th century, showing Philosophy ruling over the seven Liberal Arts (Grammar, Rhetoric, Dialectics, Music, Arithmetic, Geometry, Astronomy).

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About ethologist

Professor in the Zoology Department at Michigan State University
This entry was posted in Animals, Environment, Evolution, General, Nature of science. Bookmark the permalink.

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