Transgressions of a different sort

Before fossils were understood to be the actual remains of once-living plants and animals, they were regarded in some quarters as tricks of the devil, planted by the fallen one to test the fidelity of the faithful.

After all, fossils of animals that clearly lived in the ocean were found far from any modern ocean (like those fossil clams in Nebraska mentioned in an earlier post) and even on the tops of mountains.

At a time when the Earth and everything in it was understood to be unchanged from its original creation, fossils of marine invertebrates on mountain tops were problematic, and a divinely sent global flood was an explanation that conformed both to the observations and to the philosophical framework of the time.

We now understand the dynamic nature of the Earth and can explain these observations in terms of mechanisms like plate tectonics and glaciation.

Illustration: The last major transgression of the sea over North America formed a seaway that reached from the Gulf of Mexico to the Arctic during the Cretaceous Period (144-65 million years ago). From http://www.emporia.edu/earthsci/student/mcgee2/hipln005.jpg

Future floods?

The Earth is much more heavily populated today than it was when the great Ice Age floods occurred. If floods of the magnitude that resulted from the draining of Lake Agassiz or carving the Scablands were to happen today, the impact on humanity would be catastrophic.

Fortunately, the risk of huge, glacially induced floods like those of the Pleistocene is negligible. The mega floods of the Pleistocene were associated with continental ice sheets. Today, the only remaining continental ice sheets are in Greenland and Antarctica, and neither land mass contains large ice-dammed lakes.

Iceland’s volcanism can produce sub-glacial lakes that could cause flooding there, but not on the scale of the megafloods of the Pleistocene.

That isn’t to say that Earth is free of flood hazards; if global warming were to melt the continental ice sheets sea-level would rise 215 feet or 65 meters* but that’s another story.

* http://www.usatoday.com/weather/resources/askjack/2004-11-21-melting-polar-ice_x.htm

Image: World map showing sea level if all current ice were to melt http://www.johnstonsarchive.net/spaceart/earthicefree.jpg

Lake Agassiz

During the last ice age, a 700-mile long by 200-mile wide lake centered on the province of Manitoba covered central Canada, dammed by glacial ice.

Named Glacial Lake Agassiz, for the famous Swiss scientist and later Harvard professor Louis Agassiz, who was among the first to recognize landforms that indicated that vast continental ice sheets once covered the continents, the lake drained catastrophically when the ice dam collapsed.

Water tied up in glaciers and in glacial lakes during the last ice age caused sea-level to drop more than 100 meters. At its maximum extent, Glacial Lake Agassiz was the largest body of fresh water on the planet, and held more water than all the worlds lakes today. When the climate warmed and the ice dam was breeched, the resulting flood raised global sea levels by half a meter.

More info: http://www.cloudnet.com/~edrbsass/agassiz.htm

Source: Perkins, Sid, Once Upon a Lake, Science News November 2, 2002 v. 162:p. 283

Illustration credit: Maximum extent of Glacial Lake Agassiz,

http://mrbdc.mnsu.edu/mnbasin/fact_sheets/valley_formation.html