Download 1. The traditional divisions are physical and historical geology, often

1.
The traditional divisions are physical and historical geology, often taught as
separate, introductory courses in a one-year sequence. Physical geology deals with the
materials (minerals, rocks, water, etc.) that comprise Earth; with processes of rock
formation and decomposition; with how surface morphology is altered by the various
agents of erosion, and with how rocks deform, lands are uplifted or lowered, continents
moved, and ocean basins opened and closed through tectonic forces and lithospheric plate
movements.
Historical geology places origins of rock masses, integrated effects of geologic processes,
interpretations of ancient environments and life forms, and past tectonic movements into
the chronological framework of the geologic time scale. Thus geology is an historical
science; passage of time and evolutionary concepts are vitally important.
3.
They believed Earth to be a very young planet. Accepting such a brief geologic
history forced them to explain Earth's evolution in terms of many, rapid, short- term,
catastrophic events. Stupendous natural features like the Grand Canyon, mountain ranges,
the polar ice caps, the oceans, etc. had to develop quickly. Integrated effects of slow
movements, or of slowly operating processes, were viewed as having had little
importance in Earth's geologic history and evolution. Latter-day creationists face the
same problems with excessive geologic time compression as the eighteenth century
catastrophists. All rocks, geologic features, and life forms, extinct and living, had to have
existed simultaneously or developed at breathtaking speed, and well-studied scientific
processes such as radioactivity and molecular genetics have to be turned inside out or
denied completely. On an intellectual basis, the prolonged, uniformitarian view of Earth's
origin and geological history is much easier to accept and defend than the short time scale
of the creationists.
4.
Uniformitarianism basically says that rational observations and analyses of
modern geologic processes and events give an accurate representation of geologic
workings in the past. For example, seemingly inconsequential and barely recognizable
stream erosion can cut a Grand Canyon, given enough time. Lateral movements of a
centimeter per year can build oceans and move continents hundreds of miles, given
enough time. In addition to the slow day-to-day processes, occasional, large-scale,
powerful events (volcanic eruptions, earthquakes, meteorite impacts, etc.) occur as part of
the very long, evolutionary history of Earth. Acceptance of the uniformitarian concept
logically forces one to accept a very old age for Earth and a very long geologic time.
5.
The currently accepted age of the Earth is 4.5 to 4.6 billion years, based on
meticulous experimental measurements of lead isotopes on meteoritic and terrestrial
samples. The basic assumptions and results are supported by rubidium-strontium isotopic
age determinations on meteorite samples. This age gives the time passed since originally
dispersed, chemical constituents of the solar system were assembled into meteorites,
asteroids, planetary satellites, and planets. The oldest rocks yet dated formed about 4
billion years ago. Because Earth is a dynamic planet, most rocks we see formed much
later during Earth's history and thus are much younger than the age of the Earth.
6.
In a series of horizontal, stratified rocks, younger strata lie above older strata. This
is known as the law of superposition and assumes that all sedimentary strata were
originally deposited as horizontal layers. Fossils (remains of ancient living organisms)
changed through geologic time so that specific fossils or assemblages of fossils are found
only in strata of specific ages and are unique indicators of geologic age; this concept is
called the principle of faunal succession. Relative ages of contacting igneous and
sedimentary rocks can be determined by recognizing cross-cutting relationships and
erosional unconformities. These concepts and relationships enabled geologists to identify
and correlate rocks of similar ages anywhere on Earth and to place these rocks in their
proper, chronological order and position as the geologic time scale was developed.
7.
A hypothesis is a specific idea or explanation, the validity of which, can be tested
by observations and experimental studies. It may be one of many, different, competing
ideas or statements purporting to explain some scientific phenomenon. Depending on the
outcomes of the observations and experiments, a hypothesis can be accepted or rejected.
Hypotheses usually are directed to specific, scientific questions and issues. A theory is a
useful, currently accepted, unifying body of concepts and principles in a science. A
theory helps to explain what otherwise might be perceived as disjointed and unrelated
observations and phenomena. A theory is based on far more observations and
experiments than an hypothesis and applies to a broader range of scientific phenomena.
However, even a theory can be shaken or brought down by new observations,
experiments, and interpretations of existing data. Consider the now-discarded, static
continent theory, deeply entrenched in English and American geologic thought for the
first half of the twentieth century. With widespread acceptance of the plate tectonic
theory, the static continent idea quietly slipped into intellectual oblivion.
8.
The four, major spheres of our living environment are: 1) the atmosphere - the
gaseous envelope surrounding our planet; 2) the hydrosphere - those environments
(oceans, rivers, lakes, ice, groundwater and water vapor in the atmosphere) involved in
the hydrologic cycle; 3) the biosphere - the diverse, surficial and near-surface
environments that include all living organisms and their habitats; and 4) the solid earth the soils, regolith, and crustal bedrock layers of Earth; it hosts most of the hydrosphere,
forms the inorganic substrate for the biosphere, and interacts extensively with the
atmosphere
13.
The Earth’s internal structure is divided into layers based on differences in
chemical composition and on the basis of changes in physical properties.
Compositionally, Earth is divided into a thin outer crust, a solid rocky mantle, and a
dense core.
14.
Based on physical properties, the layers of Earth are (1) the lithosphere, the cool,
rigid outermost layer that averages about 100 kilometers thick, (2) the asthenosphere, a
relatively weak layer located in the mantle beneath the lithosphere, (3) the more rigid
mesosphere, where rocks are very hot and capable of gradual flow, (4) the liquid outer
core where Earth’s magnetic field is generated, and (5) the solid inner core.
17.
The continental shelf and continental slope mark the continent-ocean basin
transition. Important zones on the ocean floor are trenches and the extensive oceanic
ridge system.
20.
The rock cycle is one of many cycles or loops of the Earth system in which
matter is recycled. The rock cycle is a means of viewing many of the interrelationships of
geology. It illustrates the origin of the three basic rock types and the role of various
geologic processes in transforming one rock type into another.