Biology Reference
In-Depth Information
The northern lights would still drape the sky with shimmering curtains of
color, and there would be about four months of light, four months of dark-
ness, and four months of intervening dimness like that between dusk and
dawn.
Almost everything else would be different. For one thing, the climate
would be practically balmy. The mean annual temperature would be 12C°-
14°C warmer than today, in part because of an atmospheric CO
2
concen-
tration ten to twelve times that of the present. Parrish and Spicer (1988)
estimate the yearly maximum temperature in the mid-Cretaceous Arctic at
13°C and the minimum at 2°C-8°C (today the MAT is about 2°C along the
south coast of Alaska at Anchorage, and
2.9°C in the east-central interior
at Fairbanks). Occasionally, it would drop to freezing in the interior and at
the highest of the moderate elevations during the dark winter months. By
the time the asteroid hit on the Yucatán Peninsula at 65 Ma, temperatures
had declined by about 4°C and winter sea ice was forming along the north-
ern coast.
To begin our walk, a choice will have to be made between taking an east-
ern proto-Appalachian Trail or a western proto-Rocky Mountain Trail. An
ocean extends through the center of the continent from the Gulf of Mexico
to the Arctic Ocean and from the western slopes of the Appalachian Moun-
tains to the eastern foothills of the Rockies. Along the shore there are depo-
sitional basins accumulating plant and animal remains, such as those of the
dinosaurs roaming the swamps and the margins of the sea, and that later
will provide evidence of the terrestrial life of North America in the Creta-
ceous. At other places, there are deep waters in which limestones are form-
ing. These will make up deposits like the Glen Rose Formation just west of
Austin, Texas, with its numerous calcium carbonate-encased foraminifera
and extensive ammonites.
If one takes the eastern trail, it will be seen that Iceland and Greenland
are devoid of ice caps. Ice is also scant or absent from Antarctica, and this
accounts for the oceans being higher than today by about 80 m. The land
is mostly continuous across the North Atlantic to Europe, where moder-
ately high and rugged uplands include the Hercynian Mountains—whose
remnants today are found from Portugal and Spain across western Europe
north of the Alps—and the Caledonian Mountains from Scotland to Nor-
way. The North American part of this system comprises the extent of the
Appalachian Mountains from Canada to the southeastern United States.
The trail terminates near southern Georgia, where the sea wraps around
the southern end of the range and continues westward across the continen-
tal interior.
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