Geology Reference
In-Depth Information
Grasses and fl owering plants had not yet
evolved, so the dinosaurs ate the ferns
and gymnosperms that were abundant
at this time.
As a result of rising sea level, Denver
was covered by a warm, shallow sea
70 million years ago (late Cretaceous).
Marine reptiles such as plesiosaurs and
mosasaurs ruled these seas, while
overhead, pterosaurs soared through the
skies, looking for food (
◗
Figure 2).
Beginning approximately 66 million
years ago, the Rocky Mountains began
to form as tectonic forces started a
mountain-building episode known
as the
Laramide orogeny
that resulted
in the present-day Rocky Mountains.
Dinosaurs still roamed the land around
Denver, and fl owering plants began their
evolutionary history.
By 55 million years ago (Eocene),
the world was in the grip of an intense
phase of global warming. A subtropical
rainforest with many trees that would be
recognizable today fi lled the landscape.
Primitive mammals were becoming
more abundant, and many warm-
climate-loving animals could be found
living north of the Arctic Circle.
Although ice caps still covered por-
tions of North America, mammoths and
other mammals wandered among the
plains of Denver 16,000 years ago
(
◗
Figure 2
Pterosaurs (fl ying reptiles) soar over Denver 70 million years
ago. At this time, Denver was below a warm, shallow sea that covered
much of western North America. Marine reptiles such as plesiosaurs
and mosasaurs swam in these seas in search of schools of fi sh.
Figure 3). Mastodons, horses, bison,
lions, and giant ground sloths, to name
a few, all lived in this region, and their
fossils can be found in the sedimentary
rocks from this area.
What was once a rainforest, desert,
warm, shallow sea, and mountainous
region is now home to thousands of
people. What the Denver region will be
like in the next several million years is
anyone's guess. Whereas humans can
affect change, what change we will cause is
open to debate. Certainly, the same forces
that have shaped the Denver area in the
past will continue to determine its future.
With the rise of humans and technology,
we, as a species, will also infl uence what
future Denvers will be like. Let us hope
that the choices we make are good ones.
◗
◗
Figure 3
Mammoths and camels wander on the prairie during a
summer day 16,000 years ago. Whereas much of northern North
America was covered by an ice sheet, Denver sported pine trees and
prairie grass. This area was home to a large variety of mammals,
including mammoths, camels, horses, bison, and giant ground sloths.
Humans settled in this area approximately 11,000 years ago, hunting
the plentiful game that was available.
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