Geology Reference
In-Depth Information
this ability (they are
exothermic
), which is why you often see snakes or lizards
sunning themselves on rocks to warm up.
Most mammals give birth to live offspring.
Unlike the reptiles, who lay eggs, mam-
mals birth live young that must be taken care of for at least a little while before
they can fend for themselves. (I explain the exception to this characteristic — the
monotreme mammals — in a moment.)
Mammals produce milk to feed their young.
Mammalian animals have
mammary
glands
that produce milk intended to feed their offspring.
Mammals have fur or hair covering their bodies.
Modern mammals live in such a
wide variety of environments that you may not realize they all have some hair —
even elephants and whales!
Causing global cooling
A relatively recent trend among earth scientists is to view the earth's multiple systems as parts of one
large planetary system. An example is found in the
uplifthypothesis
linking cooling climate patterns
during the Cenozoic with the erosion of sediments from the Himalayan Mountains.
You may know from recent news about modern global warming that adding carbon dioxide gas to the
atmosphere increases global temperatures by thickening the layer of greenhouse gases that surrounds
the planet. Earlier in earth's history when the climate was much warmer, higher (than present) levels of
carbon dioxide and other gases existed in the atmosphere. In order for temperatures to cool down as
dramatically as they did in the mid-Cenozoic, something must have removed large amounts of carbon
dioxide from the atmosphere.
One way carbon dioxide is removed from the atmosphere is for it to be consumed during a chemical
reaction with exposed rock materials. The carbon dioxide gas first combines with rainwater in the at-
mosphere. When the rain falls on exposed rocks, the carbon dioxide links itself to elements in the rock
minerals (forming carbonate minerals), removing them and thus chemically weathering the rock. When
this process occurs, the carbon dioxide gas is no longer in the atmosphere; it is part of earth's litho-
sphere. The longer this process continues, the less carbon dioxide gas is left in the atmosphere.
The uplift hypothesis proposes that during the Cenozoic, when the Himalayan Mountains were formed
or uplifted by the collision of the Indian continent into the Asian continent, massive amounts of rock
were exposed, and the rate of chemical weathering increased. That increase removed large amounts
of carbon dioxide gas from the atmosphere, resulting in dramatically cooler worldwide temperatures.
This hypothesis is compelling in the way that it links the cycles of earth's lithosphere, atmosphere, and
hydrosphere, but it is far from proven. Scientists who study chemical weathering, atmospheric gas
concentrations, and climate change (to name a few subjects) are hard at work testing the uplift hypo-
