Geoscience Reference
In-Depth Information
CHAPTER
EIGHT
Establishing the Cause of Death
Uncovering Clues in the Rocks
To figure out what had killed all the unhatched sauropods in the eggs,
we again had to appeal to the rocks that contained the fossils. In addi-
tion to providing the only direct evidence to estimate the time of the
embryos' death, the picturesque layers of rocks at Auca Mahuevo pre-
served key clues for interpreting the cause of their death, which
appeared to be directly related to the environment in which the
sauropods had laid their eggs. The evidence for interpreting what envi-
ronment the dinosaurs had lived in would be gleaned from observing
the different kinds of rocks that formed the layers at Auca Mahuevo.
Throughout the world today, rocks are either being eroded or
formed on the surface of the earth in an ongoing cycle that has con-
tinued since the early days of earth history when the first rocks were
formed. In areas that are relatively high and steep, including the
mountains and hills that dominate all the continents, rocks are
weathered and eroded by rain, ice, and wind. Chemical reactions pro-
moted by molecules dissolved in rainwater help break the bonds
between mineral crystals forming rocks near the surface. Aided by the
destructive activity of plant roots, as well as the expansion and con-
traction of ice as it forms and thaws, loosened debris is eroded by
runoff from rains and the force of the winds. In colder regions, gla-
ciers can also serve as powerful agents of erosion, scouring away great
quantities of mountainous terrain. In areas that are relatively low and
depressed, including river valleys and lakes, some of the material
eroded away from higher regions is deposited in layers on land and in
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