Carl Alwmark

Microspectroscopic evidence of cretaceous bone proteins.

Low concentrations of the structural protein collagen have recently been reported in dinosaur fossils based primarily on mass spectrometric analyses of whole bone extracts. However, direct spectroscopic characterization of isolated fibrous bone tissues, a crucial test of hypotheses of biomolecular preservation over deep time, has not been performed. Here, we demonstrate that endogenous proteinaceous molecules are retained in a humerus from a Late Cretaceous mosasaur (an extinct giant marine lizard). In situ immunofluorescence of demineralized bone extracts shows reactivity to antibodies raised against type I collagen, and amino acid analyses of soluble proteins extracted from the bone exhibit a composition indicative of structural proteins or their breakdown products. These data are corroborated by synchrotron radiation-based infrared microspectroscopic studies demonstrating that amino acid containing matter is located in bone matrix fibrils that express imprints of the characteristic 67 nm D-periodicity typical of collagen. Moreover, the fibrils differ significantly in spectral signature from those of potential modern bacterial contaminants, such as biofilms and collagen-like proteins. Thus, the preservation of primary soft tissues and biomolecules is not limited to large-sized bones buried in fluvial sandstone environments, but also occurs in relatively small-sized skeletal elements deposited in marine sediments.

Intense and widespread seismicity during the end-Triassic mass extinction due to emplacement of a large igneous province

Multiple levels of earthquake-induced soft-sediment deformations (seismites) are concentrated in the end-Triassic mass extinction interval across Europe. The repetitive nature of the seismites rules out an origin by an extraterrestrial impact. Instead, this intense seismic activity is linked to the formation of the Central Atlantic magmatic province (CAMP). By the earliest Jurassic the seismic activity had ceased, while extrusive volcanism still continued and biotic recovery was on its way. This suggests that magmatic intrusions into sedimentary strata during early stages of CAMP formation caused emission of gases (SO 2 , halocarbons, polycyclic aromatic hydrocarbons) that may have played a major part in the biotic crisis.

The mid-Ordovician Osmussaar breccia in Estonia linked to the disruption of the L-chondrite parent body in the asteroid belt

The Middle Ordovician (466 Ma) Osmussaar breccia, situated along the northwestern coast of Estonia, is rich in angular chromite grains of extraterrestrial origin (>13 grains kg(-1)) and shocked quartz. The angularity of the chromite grains implies that they have not been transported or reworked to any large extent, connoting that the brecciation is the result of a contemporary impactor, either as a direct consequence of the impact or as a result of an earthquake triggered by the impact, and thus is not, as previously suggested, redeposited material from the nearby similar to 70 m.y. older Neugrund impact structure. The chemical composition of the chromite indicates that the impactor was an ordinary chondrite of L-type, which concurs well with the hypothesis that the influx of large bodies to Earth increased during this period due to the breakup of the L-chondrite parent body. This in turn gives support to the recent suggestion that abundant coeval mega-breccias worldwide are impact triggered. The presence of extraterrestrial chromite also strengthens the theory that physical pieces of a large celestial body can survive upon impact with Earth. (Less)

Skin of the Cretaceous mosasaur Plotosaurus: implications for aquatic adaptations in giant marine reptiles.

The physical nature of water and the environment it presents to an organism have long been recognized as important constraints on aquatic adaptation and evolution. Little is known about the dermal cover of mosasauroids (a group of secondarily aquatic reptiles that occupied a wide array of predatory niches in the Cretaceous marine ecosystems 92–65 Myr ago), a lack of information that has hindered inferences about the nature and level of their aquatic adaptations. A newly discovered Plotosaurus skeleton with integument preserved in three dimensions represents not only the first documented squamation in a mosasaurine mosasaur but also the first record of skin in an advanced member of the Mosasauroidea. The dermal cover comprises keeled and possibly osteoderm-reinforced scales that presumably contributed to an anterior–posterior channelling of the water flow and a reduction of microturbulent burst activities along the surface of the skin. Thus, hydrodynamic requirements of life in the water might have influenced the evolution of multiple-keeled body scales in advanced mosasauroids.

First known Terrestrial Impact of a Binary Asteroid from a Main Belt Breakup Event

Approximately 470 million years ago one of the largest cosmic catastrophes occurred in our solar system since the accretion of the planets. A 200-km large asteroid was disrupted by a collision in the Main Asteroid Belt, which spawned fragments into Earth crossing orbits. This had tremendous consequences for the meteorite production and cratering rate during several millions of years following the event. The 7.5-km wide Lockne crater, central Sweden, is known to be a member of this family. We here provide evidence that Lockne and its nearby companion, the 0.7-km diameter, contemporaneous, Målingen crater, formed by the impact of a binary, presumably ‘rubble pile’ asteroid. This newly discovered crater doublet provides a unique reference for impacts by combined, and poorly consolidated projectiles, as well as for the development of binary asteroids.

Impact origin for the Hummeln structure (Sweden) and its link to the Ordovician disruption of the L chondrite parent body

Several studies of meteorites show that a large disruption of an asteroid occurred ca. 470 Ma in our solar systems asteroid belt. As a consequence, a large number of meteorite impacts occurred on Earth during the following few million years. The finding and characterization, for the first time, of planar deformation features in quartz grains from rocks collected at the Middle Ordovician Hummeln structure (Sweden) prove the hypervelocity impact origin of the structure. The unambiguous shock features allow us to close an similar to 200-yr-old discussion about its origin, and further the hypothesis of enhanced asteroid bombardment during the Middle Ordovician, adding an impact crater to the increasing number confirmed and properly dated from this period. Despite its relatively small size (similar to 1.2 km in diameter), similar to the young Meteor Crater (Arizona, USA), and its old age, the Hummeln structure is remarkably well preserved, contradicting the general assumption that small craters are not preserved on Earth for more than a few tens of thousands to a couple of million years. (Less)

Comment on “Radiation History of Fossil Meteorites from Sweden” by V.A. Alexeev (2010), solar system research, 44, 311–319

We dispute the claim by Alexeev (2010) that the numerous fossil meteorites found in mid-Ordovician sediments in southern Sweden can be explained by a single large meteorite shower some 470 million years ago, and—in particular—that the reported variable cosmic ray exposure ages derived from cosmogenic 21Ne in chromite grains extracted from the fossil meteorites actually reflect variable contributions of nucleogenic 21Ne instead.

An Early Ordovician 40Ar-39Ar age for the ∼50 km Carswell impact structure, Canada

The formation age of the large (∼50 km) Carswell impact structure, Canada, has been a matter of debate ever since its discovery five decades ago, with proposed ages ranging from Mesoproterozoic to Early Cretaceous. Here, we present new 40Ar-39Ar data for aliquots of euhedral adularia, separated from vesicles in an impact melt rock from the central uplift of the structure. The analyses of the adularia yielded a statistically robust Early Ordovician crystallization age of 481.5 ± 0.8 Ma (2σ, mean square of weighted deviates = 1.06, P = 0.30). The most plausible explanation for the formation of vesicle-filling adularia is through low-temperature mineral precipitation during residual hydrothermal circulation that followed the impact, as no other known major intrusive, extrusive, or thermal events have occurred in the Carswell region in the Phanerozoic. The new age of the Carswell impact structure overlaps within uncertainty with the most precise Ar-Ar ages proposed for the L-chondrite parent body breakup event, but not with the age of the stratigraphic sequence from which the meteorites and micrometeorites from this event were recovered. Thus, either the Carswell impact represents a separate, unrelated impact event, or the dynamic evolution of the L-chondrite parent body breakup is more complicated than presently understood, and Carswell represents one of the earliest and largest known impacts of this event on Earth. (Less)

Further evidence for an impact origin of the Tsenkher structure in the Gobi-Altai, Mongolia: geology of a 3.7 km crater with a well-preserved ejecta blanket

The Tsenkher structure in the Gobi-Altai, Mongolia is a c. 3.7 km diameter crater with a well-preserved ejecta blanket. It has been hypothesized to be either of impact or volcanic origin in our previous work. Observations during our 2007 expedition and related sample analyses give further support for an impact origin. The evidence includes the presence of a structurally uplifted near-circular rim surrounded by an ejecta blanket, and abundant breccias, some of which are melt- A nd millimetre-scale spherule-bearing. Planar deformation features (PDFs) were found in one quartz grain in a breccia sample. Fe-rich grains are found in a vesicular melt sample that is also characterized by elevated platinum group element (PGE) abundances with respect to the sedimentary bedrock of the area (approximately an order of magnitude). Noble gas analysis of one breccia sample yielded an elevated 3He/4He value of (5.0±0.2) × 10-6. Although not conclusive alone, these geochemical results are consistent with a contribution of meteoritic components. A volcanic origin, in particular a maar formation, would require explanations for the unusual conditions associated with Tsenkher, including its large size occurring in isolation, the structurally uplifted rim and the lack of a bedded base surge deposit. A pronounced rampart structure observed at the eastern ejecta is also unusual for any volcanic origin. 40Ar-39Ar dating of a vesicular melt sample gives an age of the Tsenkher structure of 4.9±0.9 Ma. The rampart structure could provide insights into the formation of similar ejecta morphologies associated with numerous impact craters on Mars. (Less)