Dating catastrophes

Methods for dating mass-movement events earthquakes, volcanic eruptions and other geological hazards comprise a wide range of methods, historic, radiometric, stratigraphic and biological. For example Carbon-14 dating, applicable when the moving mass incorporated vegetation, or other radioactive elements that decay with time, surface dating of freshly exposed boulders by cosmogenic isotopes, dating of sediments by thermoluminescence, dendrochronology or lichenometry and for historic times written records or witness accounts.

Historical references are the most reliable sources for reconstructing the temporal distribution of catastrophes, especially for the last few centuries. Going further back in time, medieval time and antiquity ,the record gets poorer and more inexact. And for prehistoric time we miss descriptions of this kinds, or did we?

Considering (pre-)historic events, the oral tradition and legends all over world maybe represent first efforts to record and explain such phenomena, even if we have to be cautious, myths in geology can only be a supplementary help, not a fact, and much is left by the interpretation of stories by the compiler. Nevertheless knowing some old stories about the landscape can not be so bad for a geologist.

In the area of Seattle, Washington, at least five sites with landslide deposits or large boulders are known by local legends of the Duwamish people to be haunted by a´yahos. A´yahos are spirits with the body of a serpent and the antlers and forelegs of a deer. Old folks used to say not to look directly to an a´yahos because it could shake the ground or turn people to stone.

Non-Salish Cascadia Native representation of two -headed snakes, likely to represent spirits comparable with a´yahous. Quileute ceremonial representation of t´abale, a vicious guardian spirit on the northwestern Washington coast (from LUDWIN et al. 2007).

In 1990s geophysical investigations revealed that the area of Seattle is passed by a fault system and at least 1100 years ago an earthquake hit the entire zone- triggering mass movement all over the landscape.

Reconstructed "events" by means of oral tradition and mythological conventions.
Date range estimates used the following assumptions: a 'generation' is no fewer than 15 and no more than 40 years, events before age 5 are not remembered. the maximum lifespan is 100 years, flood survivors were 'old' when seen. and an 'old' person is at least 40. (from LUDWIN et al. 2007).

The bay of Lituya situated in Alaska is a narrow, only 2 kilometres broad, but 11 long bay open to the Pacific Ocean. The native Tlingit Indians tell that in a cavern, deep underground, lives a demon, similar in appearance to a great toad or frog. If someone dares to disturb the tranquillity of the bay, the demon will rip apart the sea and the earth and catch the intruder and transmute him to a bear.

Behind the anger of demons maybe an exceptional (yet undated) geological event hides, as a recent example shows:
On the 9th July 1958 an earthquake produced by a fault nearby triggered a rockfall, with an estimated volume of 40 million cubic metres and a weight of 90 million tons that felt from a height of 1000m in the water. The resulting wave reached a height of 524, the highest ever (human-) documented wave.

References:

FRITZ, H.M., HAGER, W.H., MINOR, H-E. (2001): Lituya Bay Case: Rockslide impact and wave run-up. - Science of Tsunami Hazards 19(1), 3-38.
LUDWIN, R.S. & SMITS, G.J. (2007): Folklore and earthquakes: Native American oral traditions from Cascadia compared with written traditions from Japan. From PICCARDI, L. & MASSE, W.B: (eds): Myth and Geology. Geological Society, London, Special Publications, 273: 67-94
LANG, A.; MOYA, J.; COROMINAS, J.; SCHROTT, L. & DIKAU, R. (1999): Classic and new dating methods for assessing the temporal occurrence of mass movements. Geomorphology 30:33-52

An Animal Fable from the Upper Cretaceous

The modern tale "Homchen - ein Tiermärchen aus der oberen Kreidezeit" (Homchen - An Animal Fable from the Upper Cretaceous), was published in 1902 by the German author Kurd Laßwitz (1848-1919), considered a founder of the German science-fiction movement.

Homchen is a highly evolved marsupial of the Kala-tribe, living in a world dominated by the great lizards. In a world ruled by ignorance and oppression, Homchen rebels against the saurian warlords, and is banned from the society of mammals. He then decide to search the red snake, creator of the reptilian world, but the dinosaurs, and especially the "dainty beak's", high priests of the red snake, try to stop him at any costs.

A sketch by Laßwitz of Homchen of the Kala tribe - clearly inspired by a Koala. Laßwitz considered human evolution as a straight forward process from rodents to marsupials to placental mammals and finally humans.

"You know what the red serpent will do, if you don't obey? He will swallow the sun, until it will be small and cold. And the day will be like the night, and all water will be frozen. The trees lost their leaves and the grass will be covered by white ash, so nobody will find something to eat. The reptiles that didn't starve, will be suffer great cold, and finally they will be unable to move. Then the animals of the night will rise, protect by their fur, and they will scratch the eyes from your faces, like Kala did to the hollow-bone. The mammals will eaten your flesh, and your bone they will throw against the sun, until it fall from sky and the eternal night begin."

Mission CryoSat-2

Source: Project Cryosat and Cryosat-2

The ice in the polar regions play a crucial role in earths climate, but the quantification of the ice and measuring it's change trough time is difficult.
Satellite images provide a good tool to determinate the area, but the thickness can only measured on single points by costly drilling trough the ice. New generation satellites, like the American "Icesat" use RADAR technology to determinate precisely the ice thickness, but snow cover and water are still a problem, and can distort the measurements. After the failure tof the European Space Agency to send a new generation satellite - Cryosat (crashed only few seconds after the start in 2005)- in the orbit, now his brother - Cryosat2- is almost ready.

In December the satellite will leave Munich (Germany) to be transported to the Kazakhstan spaceport Baikonur, from where it will be send in February 2010 with a modified rocket (a former atom weapon carrying Dnepr model) in space.
With a new RADAR-altimeter ("Siral") Cryosat2 will take 20.000 measurements per second in the next three years with an unequalled precision, and be able to determinate changes of thickness in ice of only few centimetres.

Meanwhile reports of Canadian researches under David Barber (University of Manitoba) confirm the receding trend of the ice cover in the Arctic. On 12 September 2009 the ice covered 5,1 million square kilometres, only 2007 and 2008 the area was lesser compared to the mean value of the 30 years of satellite measurements. Compared to the long term observed between 1979 and 2000, the remaining actual ice cover is also 70% of the former area, the area of long lasting ice diminished from 90 to 17%.
Not only the area is declining, also the thickness is inferior, in some areas the thickness diminished from 10m to 2m. The thinner ice is more fragile, and can not resist wave movements or storms.

Biologists are concerned about the status of the polar bear, with a valued population of 25.000 animals: the ice is in vast regions to thin to be used by the animals to hunt, and the sea freeze later in the year.
In the area of Churchill, in the Canadian province of Manitoba ,the biologist Ian Sirling (Canadian Wildlife Service) observed a possible related fact - an increasing of cannibalism events from elder on younger animals.

150 years

An abstract still evolving...

Darwin's rat and other strange mammals

"I had no idea at the time, to what kind of animal these remains belonged".

C. Darwin 1839

During the first two years of his voyage aboard HMS Beagle, Charles Darwin collected a considerable number of fossil mammals from various localities in Argentina and Uruguay. He recovered his first fossils at Punta Alta on September 23, 1832, and the last two years later at Puerto San Julián.
The fossils were packaged and sent to his former mentor the botanist/geologist John Stevens Henslow, deposited in the Royal College of Surgeons in London, and finally studied and named by Richard Owen between 1837 and 1845. Based on the fossil material Owen described a variety of Pleistocene mammals, including Equus curvidens, Glossotherium sp., Macrauchenia patachonica, Mylodon darwini, Scelidotherium leptocephalum and Toxodon platensis.

Unfortunately during April 10 and 11.1941 the paleontological collection of the Royal College was heavenly damaged by bombardment, almost 95% of the collection got lost. Beginning in 1946 the remaining material was transferred to the Natural History Museum in London, where it is still housed.

Fossils were known in South America since before the Spanish conquistadores, but interpreted as the remains of mythical creatures or giants annihilated by the gods. In 1774 the English Jesuit Thomas Falkner wrote:
"On the banks of the River Carcarania, or Tercero, about three or four leagues before it enters into the Parana, are found great numbers of bones, of an extraordinary bigness, which seem human. There are some greater and some less, as if they were of persons of different ages. I have seen thigh-bones, ribs, breast-bones, and pieces of skulls. I have also seen teeth, and particularly some grinders which were three inches in diameter at the base. These bones (as I have been informed) are likewise found on the banks of the Rivers Parana and Paraguay, as likewise in Peru. The Indian Historian, Garcilasso de la Vega Inga, makes mention of these bones in Peru, and tells us that the Indians have a tradition, that giants formerly inhabited those countries, and were destroyed by God for the crime of sodomy. I myself found the shell of an animal, composed of little hexagonal bones, each bone an inch in diameter at least; and the shell was near three yards over. It seemed in all respects, except it's size, to be the upper part of the shell of the armadillo; which, in these times, is not above a span in breadth."

22 years later the French naturalist George Cuvier published the first scientific work on a fossil South American mammal, and named it the giant sloth Megatherium americanum. In 1806 Cuvier described preliminary three proboscidean types, attributing them to the genus Mastodon. After these first investigations, there was almost no further research, in 1838 Owen wrote in his opening paragraph on his work on the fossil mammals collected by Darwin:
"It may be expected that the description of the osseous remains of extinct Mammalia, which rank amongst the most interesting results of Mr. Darwin's researches in South America, should be preceded by some account of the fossil mammiferous animals which have been previously discovered in that Continent. The results of such a retrospect are, however, necessarily comprised in a very brief statement; for the South American relics of extinct Mammalia, hitherto described, are limited, so far as I know, to three species of Mastodon, and the gigantic Megatherium."

The young Darwin got some of the first fossil determination wrong, so he attributed found osteoderms (regarded by Owen to belong to the giant "armadillo" Glyptodon) to Megatherium, following a reconstruction by Cuvier of an armoured ground sloth, and molars of Toxodon as remains of a giant rodent (but even Owen admitted that these teeth's bear a certain resemblance to those of rodents).
Owen by his part got the general relationship of this mammals incorrect, attributing some genera closer to existing animal-groups then they were in fact.
Influenced by the proposal of Owen, Darwin got convicted that "The most important result of this discovery, is the confirmation of the law that existing animals have a close relation in form with extinct species." (1839), surely a further clue for Darwin that species are not isolated and immutable in time.

Ironically in the error of Darwin there is a ray of truth, toxodonts are today considered highly derived native South American ungulates, distantly related phylogenetically to rodents and guanacos, whereas the large glyptodonts are not the ancestors of armadillos, but to the contrary, the latter are antecedent to the former.

Frederick Waddy: Richard Owen "Riding His Hobby" (1873)

References:

FERNICOLA; VIZCAINO & DE IULIIS (2009): The fossil mammals collected by Charles Darwin in South America during his travels on board the HMS Beagle. Revista de la Asociacon Geologica Argentina. 64(1): 147-159

Extinctions & Excrements

"dal letame nascono i fior
dai diamanti non nasce niente"
From dung flowers are born
From diamonds nothing comes
"Via del Campo", Fabrizio de André (Italian poet-musician)

Until 20.000 years ago North America showed a biodiversity of large mammals comparable with modern Africa, if not greater. 10.000 years later 34 genera with animal-species weighing more than a ton were extinct.

The extinction of the Pleistocene Megafauna is still an unsolved mystery. The proposed hypothesis range from overkill by human hunters to a meteor impact and climate change at the end of the last glacial maximum. Geologically speaking it happened suddenly, but a new study now maybe can date more precisely the extinction pattern and duration, using an unusual data source - fossil excrements and the inhabitants of this "biotope".

In 2005 and 2006 sediment cores with a complessive length of 11,7m were taken from Appleman Lake and compared with other cores of lakes in the U.S. State of Indiana.
Thirteen wood, pollen and charcoal samples, recovered from the lacustrine sediments, were dated by radiocarbon method on ages between 7.000 and 14.000 yr BP and used interpolate an age-depth model of the core.

The fungus-genus Sporomiella lives on animal dung and the spores have to pass the digestive tract of large herbivores to germinate. The spores can also accumulate in sediments along with other micro- and macrofossils like pollen and charcoal, so the presence of the fossil spores in sediments correlates with the amount of excrements - "Lots of dung means lots of spores" (JOHNSON 2009), and the amount of dung can give a hind to extrapolate the size of the population of herbivorous animals like mastodon or mammoth.

The timing of the Sporomiella decline and the first major charcoal peak are well constrained by two dates between 14.6 and 14.7ka. The wood pollen (Quercus and Pinus) increases between 10.7 and 12.2 ka.

Figure from GILL et al. 2009: Appleman Lake time series for (A to F) percent pollen abundances of selected taxa (NAP, nonarboreal pollen), (G) Sporormiella and (I) charcoal counts.

Applying this method, Gill et al. found that the amount of spores first decreases slowly, and only in 14.800 years old sediments the number of spores decreases significantly. To old for the proposed impact, and also to old for a climatic or environmental change - vegetation change, interpolated from the pollen assemblage, namely happens only after the faunal demise, and is more probable caused by the extinction of large herbivore, then the cause of extinction.

The greatest impact of humans - in form of the Clovis Culture - on the Pleistocene landscape in North American was supposed in a time interval between 13.330 and 12.900 years ago. The new data predates the Clovis, nevertheless archaeological findings support a lesser tool specialised pre-Clovis culture in the time interval of the Megafauna collapse, so human influence could not be ruled completely out.

Figure from JOHNSON 2009.

The changing environment after the Megafauna collapse, from an open savanna with scattered trees to a spruce-broadleaf woodland, was the result of ceased pasture of shrubs and trees by Mammoth and Co. The expansion of woodlands is also supported by a larger amount of charcoal in the sediments, from time to time the woodlands caught fire, and the ash was eroded, transported and finally deposited in the examined lakes.

Even if the new method con not give us the definitive answer, at least it's provide some new data to better understand the temporal progress and the environmental change of the late Pleistocene extinction event.

References:

GILL et al. (2009): Pleistocene Megafaunal Collapse, Novel Plant Communities, and Enhanced Fire Regimes in North America. Science 326: 1100-1103 http://www.sciencemag.org/cgi/content/abstract/326/5956/1100

GILL et al. (2009): Supporting Online Material for Pleistocene Megafaunal Collapse, Novel Plant Communities, and Enhanced Fire Regimes in North America. Science 326. www.sciencemag.org/cgi/content/full/326/5956/1100/DC1

JOHNSON (2009): Megafaunal Decline and Fall. Science 326: 1072 - 1073. http://www.sciencemag.org/cgi/content/short/326/5956/1072

Interview to Dr. Jacquelyn Gill by the Canadian Broadcast: mp3 (4MB)

--------- Thanks to Ole Nielson for linking to the post----------

Cool Artiodactyls

Islands seem to have own rules concerning evolution, forming unusual animals like dwarfing elephants and gigantic rats. But islands are in fact unusual habitats with limited resources and so available energy. To survive special adaptations are necessary to economize this energy. Ectotherm vertebrates, like reptiles, are specialists in coping with low levels of available energy, but doing so these animals display an inconstant growth - with times of low or ceasing growth when conditions are unfavourable. Endotherm animals, like mammals have high and steady growth rates, but the necessity of constant food - energy - input, on a confined island a possible problem. But the Pliocene-Pleistocene "cave goat" or "Mouse-goat" Myotragus balearicus after a new study by Köhler & Moyá seems to have combined the best parts of being reptile and mammal together.

Myotragus balearicus (wikipedia)

Studying fossil material of this extinct species, the researchers have noted in bone transects cyclic LAGs - lines of arrested growth. This pattern was until now unknown in mammal bones, even if single lines were known in cervids, the physiology of Myotragus seems to have used this strategy repeatedly. Myotragus grew at slow and variable rates; growth could also be arrested completely to save precious energy. With this strategy the species managed to survive on the resource poor island of Majorca for more then 5,2 million years, until humans colonized the island, and, like many times before and after, forced the species to extinction.