Geoscience Reference
In-Depth Information
CHA PTER SEVEN
Establishing the Time of Death
Evidence from Clocks in the Rocks
Just as fossils provide important information about life-forms that
inhabited our world in the distant past, the rocks that they are pre-
served in constitute our only evidence to interpret when these ancient
animals lived. To recount this part of our investigation, we need to
flash back from the lab to the field.
What originally attracted us to explore the site that contained the
eggs and embryos in Patagonia was the stunning visual beauty of the
area's rocky outcrops. Layer upon layer of crimson sandstone and mud-
stone form a fantasyland of banded ridges and flats at Auca Mahuevo.
This maze of ridges and ravines took nature millions of years to con-
struct. First, the layers of sand and mud were laid down across the
landscape when the dinosaurs lived. Then, these layers were buried
under a thick blanket of subsequently deposited layers and remained
under the surface of the earth for millions of years before the power-
ful tectonic and volcanic forces that created the mountains and val-
leys of the region lifted them back toward the surface. As they rose,
rain and wind eroded the overlying layers of rock, leaving the ancient
layers exposed on the surface once again. And once they became
exposed, the rain and wind sculpted them into the breathtaking
landscape spread out before us.
We knew from our experience in other expeditions that these
kinds of exposures sometimes contained buried caches of fossil trea-
sure. So as we drove down toward the badlands under the radiant
morning sun that greeted the second day of our expedition, we could
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