Geoscience Reference
In-Depth Information
distinct states of the same material (e.g. cryosphere-
hydrosphere). The majority also features differential
movement across them: these are
boundary layers
(discussed later in this topic). Compare and contrast this
dynamism with the static interfaces of the Moon and those
thought to be present on other rocky planets.
1.6
Subtle, interactive Earth
Prior to the now widespread acceptance of diversity,
complexity, and interactions among the natural and
environmental sciences, it was common for physicists and
engineers to look upon Earth as a gigantic machine. They
only had to understand how all the various parts worked
and by a process of integration put all the components
together so that Machine-Earth would then be under-
stood; it would do work at rates set by the outflow of heat
energy from the interior and the input of external solar
energy. While individual parts of the Earth system
undoubtedly benefit from this approach, and ultimately
we will fully understand Machine-Earth, interactions
between subparts are so various that they create a richer
and more complex Earth than we often realize. It is this
complexity that often attracts students of the Earth and
environmental sciences today. Crucially, present Earth
does not, and indeed cannot, sample all possible scenarios
of complexity that might arise, for this is time dependent
and stochastic, that is, it depends upon a degree of chance.
Time is certainly something Earth has in plenty; the planet
has operated as a coherent body for
reflectivity (albedo) from the shiny white ice and snow-
covered surface (Fig. 1.17). Can you think of an example
of negative feedback?
1.6.2
Fluid turbulence
Turbulence is a characteristic of fluid flow (Fig. 1.18) that
dominates many Earth systems, chiefly atmosphere, rivers,
and oceans. It is a difficult subject; a famous physicist is
said to have remarked that when he eventually arrived in
Heaven he would want to ask the Omnipotence about the
origin and nature of two phenomena: quantum electrody-
namics and turbulence. But he only expected to be able to
understand the former! This is because we cannot predict
the
exact
magnitude of local turbulent flow velocity at any
point in time or space because the velocity depends on that
which existed previously; it is both the cause and result of
the turbulent motion. Instead, recourse is made to statisti-
cally determined quantities, like mean velocity and devia-
tions from this mean expressed as fluctuations.
4.5 Gy, and during
this time it has experienced many of the combinations of
interacting variables that matter, energy, space, and time
can throw at it (though not all - witness the “runaway
greenhouse” climate of Venus). It is the task of the geo-
scientist to try to decipher the past history of Earth,
informing the Earth/environment “process-engineers”
who study the present system of the exact nature of time
dependency. Our intention here is not to confuse the
mechanistic issues that form the content of the following
sections of this topic, but instead to draw the reader's
attention to some interesting consequences of interaction.
1.6.3 Chaos theory - randomness in deterministic
systems (butterflies and cyclones)
Two solutions to certain differential equations using
parameters differing by only 0.001 are initially identical,
1.6.1
Inter- and intra-system feedbacks
In everyday life, feedback is a message considered returned
from audience to speaker or operator. In nature, feedback
is also a return of usually energy within or between func-
tioning systems. Thus a growing ice cap in a cooling
climate further cools the surrounding atmosphere by posi-
tive feedback due to enhanced shortwave solar energy
Fig. 1.17
Expanding ice sheets give positive feedback to cooling
because of their high albedo/reflectivity of shortwave incoming
radiation.
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