Channeled Scablands

Geologists long recognized that something was odd about the landscape of eastern Washington state. The landscape is marked by dry canyons and deeply eroded basalt flows—the channeled scablands. In other areas, parallel ridges of undulating low hills cover the bedrock.

In the 1920s geologist J Harlen Bretz interpreted these features as the result of erosion and deposition from floods originating with the breach of glacially dammed lakes—the ripple-shaped hills (shown in the aerial view photo) were exactly that—giant ripples deposited by enormous outpouring of water from Glacial Lake Missoula.

The channeled scablands formed around 15,000 years ago after an ice dam holding back the waters of glacial Lake Missoula failed, sending 2,000 cubic kilometers of water rushing through the breach and reshaping the landscape in a matter of days.

Further info: http://www.nps.gov/history/history/online_books/geology/publications/inf/72-2/intro.htm

Photo credit: http://hypography.com/forums/earth-science/12606-missoula-floods-channeled-scablands-drumheller-channels.html

Before the Chunnel

Half a million years ago England and France shared a land connection that also formed the dam for a glacial lake that covered much of northern Europe.

The soft chalk bedrock dam was breached by the waters of the glacial lake between 450 and 180 thousand years ago, forming the Strait of Dover. As with the torrent that breached the Straits of Gibraltar and filled the Mediterranean, modeling indicates that waters rushed through the Dover Strait at rates up to 1 million cubic meters per second.

The evidence for this rush of water comes from sonar imaging of the submerged valley carved by the flood waters. Broad grooves up to 100 meters wide and 15 km long were carved into the valley floor. These features indicate high flow rates, and are associated with other mega floods.

Source: Birth of an Island: Megaflood severed Europe from Britain. SN July 21, 2007, v. 172, p. 35; based on Gupta, S., et al., 2007. Nature July 19

Illustration credit: http://islesproject.com/2009/01/12/450000bce-200000bce-the-origins-of-island-consciousness-the-torrent-that-created-the-english-channel/

Real flood geology

Imagine a dry basin where the Mediterranean now sits. 5.6 million years ago the Mediterranean was closed off from the Atlantic Ocean by tectonic uplift, and its waters gradually evaporated, leaving behind tell-tale deposits of evaporate minerals and creating what geologists call the Messinian salinity crisis.

About 5 million years ago Atlantic waters breached the barrier at the Strait of Gibraltar creating an enormous flood. Recent modeling indicated that water may have poured into the Mediterranean basin at a rate 1,000 times the flow of today’s Amazon River, filling the basin in less than two years—a geological blink of an eye.

Source: Daniel Garcia-CAstellanos, et al, December 10, 2009 Nature.

Illustration credit: http://records.viu.ca/~earles/messinian-crisis-apr03.htm

Shields up, Scotty

Early Earth was a rough place for life to gain a foothold.

One of the questions facing scientists is just when the earth’s protective magnetic field was strong enough to shield its inhabitants from harmful cosmic radiation.

Ancient rocks from South Africa indicate that a magnetic field 50-70 percent the strength of today’s magnetic field was in place by 3.4 billion years ago.

The evidence comes from nanometer-sized crystals of the mineral magnetite embedded in millimeter-sized quartz crystals. Quartz is the most stable mineral in the Earth’s crust and a good time capsule for the included magnetite. A magnetometer is used to detect the magnetic signal preserved in the iron atoms in the magnetite and to measure the strength and orientation of the ancient magnetic field.

[Note: Not just any rocks can be used in analyses in dating ancient geological events, because millennia of deformation and reworking of the Earth’s crust could re-set geological timepieces, so great care is taken in selecting the best candidates for dating.]

Source: Tarduno, John, et al., March 5, 2010 Science.

Grossman, Lisa, Shields were up on early Earth. Science News March 27, 2010, p. 12.

Bridging the gap

The island of Madagascar is separated from Africa by the Mozambique Channel, 460 km across at its narrowest point and up to 3,000 meters deep. Scientists have long debated how the four-legged inhabitants of Madagascar got there, especially the non-aquatic ones.

Seventy years ago paleontologist George Gaylord Simpson proposed a “sweepstakes” model in which small vertebrates could have been transported from the African mainland to Madagascar on natural rafts of floating vegetation.

The problem with Simpson’s idea was that today’s currents flow westward from Madagascar towards Africa. But 60 million years ago continents lay in different positions, and new paleo-oceanographic modeling shows that there was a strong current from Africa to Madagascar, which would have provided the route for the sweepstakes rafts with their accidental migrants onboard.

It took a while, but Simpson's 20th century hypothesis was verified with the help of 21st century technology.

References: http://www.oceandots.com/indian/mozambique-channel/

Ali, Jason R., and Huber, Matthew, 2010. Mammalian biodiversity on Madagascar contolled by ocean currents. Nature 463: February 4

Map is from http://www.embassy.org/madagascar/madagasc.jpg

First footprints, revisited

GeoLog has previously reported on the first footprints made on land, tracks in 530-million year old sandstone made by some sort of invertebrate animal, probably an arthropod—a millipede, perhaps. Now comes word of the oldest known footprints of a four-legged vertebrate, or tetrapod, in rocks 395 million years old.

This find is significant because the tracks predate the oldest known tetrapod body fossils by 18 million years, and if these tracks are indeed made by tetrapods, the find would push back the timing of the vertebrate transition from water to land.

In the absence of accompanying body fossils, it is difficult to definitively match trackways with track-makers, and one alternative explanation is that these trackways could have been made by lobe-finned fishes, precursors to the tetrapods.

[One more note: The trackways represent several different animals ranging from an estimated 50 centimeters long to 2 and a half meters long—quite a large animal for so early in tetrapod evolution.]

Sources: Grzegorz Niedźwiedzki, Piotr Szrek, Katarzyna Narkiewicz, Marek Narkiewicz & Per E. Ahlberg ^{Nature 463, 43-48 (7 January 2010) Tetrapod trackways from the early Middle Devonian period of Poland}

Perkins, S., 2010, Fossil footprints could push back origin of first four-limbed animals. Science News January 30, 2010.

Battling Beetles

Antlers and horns are usually associated with the male of the species, but sometimes the females bear battle armor.

Female dung beetles have horns that are used in challenging other female dung beetles for dung. Dung beetles lay their eggs in dung, and researchers have found that females with more robust horns produced more offspring than females of similar size but with smaller horns.

Experiments also showed that, unlike males, who may sport extravagant ornament to advertise their superior genetic makeup and suitability as a mate, female ornament does not play a role in sexual selection, at least among dung beetles. So it appears that development of showy weaponry in female dung beetles is related to survival in procuring resources, while in males it functions for survival of a different sort.

Sources: Millus, S., Female beetles ready for dung wars. Science News March 27, 2010

Watson, Nicola and Simmons, Leigh, Proceedings of the royal Society B, March 3, 2010

Watson and Simmons, Behavioral Ecology, March-April, 2010

Photo credit: Sean Stankowski