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Earth Layers
Name: Donna
Status: Educator
Age: 40s
Location: N/A
Country: N/A
Date: February 15, 2004
Question:
I have a question regarding the
earth....crust or ??
I
have discovered the 3-4 layers of the earth, but am
onfused about some
things.....
I thought there were layers such as:
Top soil
Clay
Rock
Water
Oil
Etc..... (not in this order)
Under the topsoil that we see........is this not
true?
Replies:
Hi Donna!
At the present development the zonal structure of the
plabet Earth is considered to be divided into 3
principal regions:
crust, mantle and core.
The crust has a variable thickness, being 35-70 km
thick in the continents and 5-10 km thick in the ocean
basins. The crust is composed mainly of
alumino-silicates.
1)The crust is the upper region and is about 40 kms.
(25 miles) thick in continental regions, beeing
highly heterogeneous, composed mainly of rocks of
variable composition between granite and basalt.
Covered by the oceans, the crust is about 5-10 km. (
3-6 miles) thick( in the average) and believed to be
composed mainly by alumino-silicates.
2) Below the crust is the mantle, that goes down for
2,900 km (1,800 miles). The mantle is solid. It is
believed to be composed mainly by magnesium silicates
with lesser amounts of iron, calcium and aluminum
silicates and divided into layers characterized by
different types of minerals.
3) Further below is the core that is believed to be
mainly composed of metallic iron, nickel and some
sulfur all in the molten state.
At about 5,080 km (3,160 miles) there is the inner
core composed mainly also by iron. This iron is under
a very high pressure so it is in solidified.
And...thanks for asking NEWTON!
Mabel
(Dr. Mabel Rodrigues)
The items listed in the question are all relatively near the surface and
components of the crust. However, the sequence and composition of layers
near the surface is strongly dependent on local geology. For instance, oil
is only found in certain places. In other places, the crust is very
different. I suggest you contact the geological survey office for your
state for information on your local conditions and a basic text on geology
and earth science for definitions of the items you have listed.
You can find links to all the state geological surveys in the US at the
Association of American State Geologists, which is hosted by the University
of Kansas. Their link is:
http://www.kgs.ukans.edu/AASG/AASG.html
Andy Johnson
The Earth does have four distinct layers---inner and outer cores, mantle and
crust (there are some other sub-layers that geologists talk about, but for
our purposes, we'll stick to the big ones). The Earth is huge, and the crust
is like the skin of an orange in comparison--not very thick compared to the
overall size. All of the activity that you mentioned occurs in and on the
crust. There are many layers in the crust resulting from many geologic
processes. Some of these layers are rocks (igneous, metamorphic or
sedimentary) or some transition stage (for example rocks and sand) in the
rock cycle. Sometimes economically important materials like oil are trapped
in rocks. You don't say where you are, but I am in the Chicago area, and if
I dug a hole, I would go through soil, glacial materials, then different
layers of rock (for example, limestone which was deposited long ago when this
area was covered by a shallow sea). If I could keep going, I would go into
the mantle, the outer core and inner core. It is difficult to grasp the
scale and enormity of the Earth, and your struggle with it is common. It is
hard to look at things like the Grand Canyon and really understand that it is
a fraction of the depth of the Earth itself.
Pat Rowe
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