Geoscience Reference
In-Depth Information
CO
2
CO
2
Weathering
f
(temp)
Volcano
Ca
2+
+ 2HCO
3
-
→
CaCO
3
+ CO
2
+ H
2
O
CaCO
3
Subduction
Figure 1.2. the carbon cycle as it acts to regulate earth's surface temperature. redrawn
from kasting (2010).
The logic goes like this. Carbon dioxide is constantly introduced from
the interior of Earth into the atmosphere. The CO
2
comes from volca-
noes and from hydrothermal vents at the bottom of the ocean. How-
ever, if we look carefully, we see that these CO
2
sources, at least most of
them, originate as a result of Earth's continuous churning in a process
known as plate tectonics. In practice, the loss of heat from Earth's inte-
rior (estimated at some 5000°C in the middle) causes the mantle (the
layer just below Earth's crust) to move and mix in a process known as
convection. This convection creates regions of volcanic outpourings,
mostly into the oceans, that divide Earth's crust into a series of mobile
plates riding on the mantle below. As new ocean floor is formed by this
process, old ocean floor is also injected back into the mantle in a pro-
cess known as subduction (see
ig. 1.2)
. This is a violent process generat-
ing most of the major earthquakes, and it is a prime builder of mountain
ranges. So, CO
2
is liberated to the atmosphere, but it doesn't accumu-
late forever. Indeed, it is actively removed by a process known as chemi-
cal weathering, where the CO
2
reacts with rocks at Earth's surface.
7
A
particularly interesting aspect of weathering is that it is temperature sen-
sitive; it goes faster at higher temperatures.
With this in mind, we can start to imagine how planetary-scale tem-
perature regulation might work. If atmospheric temperature gets too
