Ping! Please take the Geoblog survey

Some of you may not yet have noticed the new geoblog survey which aims to collect representative data on the geoblogosphere. Sorry for using this rather unusual mass pingback to attract your attention on this.. but the survey will only be online until the first of November 2009.
So please take the survey, it only takes some minutes..




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New candidate smoking gun for K-T boundary

So far, the Chicxulub crater has not convinced me as the source of the global iridium anomaly that marks the K-T boundary. Other extinction events have already been linked with trap volcanism (P-T boundary, T-J boundary [see also this blog entry]) and therefore I had always favoured the Deccan traps as a major contribution to the environmental changes that lead to major extinction at the K-T boundary.

Now I might be able to have the cake and eat it. A structure known as the "Bombay High", which previously has been investigated as a reservoir of hydrocarbons, is now tentatively identified as a meteorite crater. Since the object that made this crater must have had a diameter of 40 km, comparable to the asteroid Ganymed, the crater should actually be classified as an asteroid crater. With a diameter of 500 km it would also be the largest known impact structure and much younger than impacts of comparable size.



The GSA press release says:

"It's hard to imagine such a cataclysm. But if the team is right, the Shiva impact vaporized Earth's crust at the point of collision, leaving nothing but ultra-hot mantle material to well up in its place. It is likely that the impact enhanced the nearby Deccan Traps volcanic eruptions that covered much of western India. What's more, the impact broke the Seychelles islands off of the Indian tectonic plate, and sent them drifting toward Africa.

The geological evidence is dramatic. Shiva's outer rim forms a rough, faulted ring some 500 kilometers in diameter, encircling the central peak, known as the Bombay High, which would be 3 miles tall from the ocean floor (about the height of Mount McKinley). Most of the crater lies submerged on India's continental shelf, but where it does come ashore it is marked by tall cliffs, active faults and hot springs. The impact appears to have sheared or destroyed much of the 30-mile-thick granite layer in the western coast of India.

The team hopes to go India later this year to examine rocks drill from the center of the putative crater for clues that would prove the strange basin was formed by a gigantic impact."

Sankar Chatterjee, The significance of the contemporaneous Shiva impact structure and Deccan volcanism at the KT boundary, 2009 GSA Annual Meeting, Portland, OR. [Abstract]

The Cambrian Explosion: How tectonics drove evolution

If life had been around on the planet for three billion years already, why did multi-cellular organisms (metazoa) only appear 540 million years ago? But when multi-cellular organisms appeared on the plan, they radiated quickly into very many species. The radiation happened so fast, it was dubbed the "Cambrian Explosion".

In a paper in print at Molecular Biology and Evolution Xavier Fernàndez-Busquets et al. looked at sponges to understand what holds them together in a way that is different to bacterial colonies. Sponges are the oldest extant Precambrian metazoan phylum and thus a valid model to study factors that could have unleashed the rise of multicellular animals. One such factor is the advent of self/non-self recognition systems, which would be evolutionarily beneficial to organisms to prevent germ cell parasitism or the introduction of deleterious mutations resulting from fusion with genetically different individuals.

The molecules responsible for self/non-self recognition systems probably evolved gradually before the Cambrian period. Sponge cells associate through calcium-dependent, multivalent carbohydrate-carbohydrate interactions of the g200 glycan found on extracellular proteoglycans. Fernàndez-Busquets et al. propose that stronger cell adhesion allowed the integrity of genetically uniform animals composed only of "self" cells, facilitating genetic constitutions to remain within the metazoan individual and be passed down inheritance lines.

Thus, the Cambrian explosion might have been triggered by the coincidence in time of primitive animals endowed with self/non-self recognition, and of a surge in sea water calcium that increased the binding forces between their calcium-dependent cell adhesion molecules. The increase of sea water calcium would be the product of increased tectonic activity and resulting chemical erosion.

Fernandez-Busquets, Xavier, Andre Kornig, u. a. (2009), Self-recognition and Ca2+-dependent Carbohydrate-carbohydrate Cell Adhesion Provide Clues to the Cambrian Explosion, Molecular Biology and Evolution, msp170, doi:10.1093/molbev/msp170.

New geoblog survey

Lutz Geissler, Callan Bentley and myself have prepared a new survey which aims to collect representative data on the geoblogosphere. The ultimate goal is to prepare a manuscript and submit it to an international geo journal to spread the spirit of the geoblogosphere.

The survey will be online until the first of November 2009. First results will be presented at the AGU fall meeting by Callan.

Coral reefs in a thermal crisis

Coral reefs were among the systems hardest hit by the end-Triassic events. Volcanism associated with the breakup of Pangaea released enormous amounts of CO2 into the atmosphere. The increased greenhouse effect and the acidification of the oceans caused a widespread extinction. The large and highly diversified reefs of the Triassic disappeared. One of the few survivors was a reef situated in what today is the south of France.

Wolfgang Kiessling of the Museum für Naturkunde Berlin (Berlin Museum of Natural History) and co-workers went at answering the question why this particular reef survived the extinction event and what lesson can be learnt for estimating the effects of the current environmental change through elevated atmospheric CO2 levels. The surviving European reefs later formed the nucleus for the re-radiation of corals. The recovery, however, took a very long time: 15 million years.

In their work, published in the latest issue of Palaios, they come to the conclusion that the reef was situated in deep shelf waters at high latitudes in a region that had been a hotspot of coral reefs already through the Triassic. Their findings also highlight the importance of deep shelf regions for the survival of marine species. It is not always necessarily remote ocean islands.

Kiessling W., Roniewicz E., Villier L., Léonide P., Struck U. 2009. An early Hettangian coral reef in southern France: Implications for the end-Triassic reef crisis. Palaios, 24: 657-671. doi:10.2110/palo.2009.p09-030r