T-P-G-variathhhhffffsdjkkjhhdsfghhion.pdf

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1. VARIATION OF TEMPRATURE WITH DEPTH
Temperature increases with depth: Geothermal gradient
is therate of
increasingtemperaturewithrespectto
increasing
depth
into
the
Earth
's
increasing
depth
into
the
Earths
interior. Away
from
tectonic
plate
Away
from
tectonic
plate
boundaries, it is about25°C per km ofdepth
inmostoftheworld

2. TheEarth's internal heat
comes from a combination ofresidual
heat from planetary accretion
,heat produced
through
radioactive
decay
and
possibly
heat
from
other
sources
through
radioactive
decay
,
and
possibly
heat
from
other
sources
The
major
heat
-
producing
isotopes
in
the
Earth
are
potassium
-
The
major
heat
-
producing
isotopes
in
the
Earth
are
potassium
-
40
,uranium-238
,uranium-235
,andthorium-232
As
much
of
the
heat
is
provided
by
As
much
of
the
heat
is
provided
by
radioactive decay, scientists believe that
early in Earth history, beforeisotopes with
short
half
lives
had
been
depleted
Earth
's
short
half
-
lives
had
been
depleted
,
Earths
heat production would have been much
higher

3. Half-life(t
½
) is the amount of time required for a quantity to fall to
half its value as measured at the beginning of the time period.
Number o
f
half-lives
elapsed
Fraction
remainin
g
Percentage
remaining
elapsed
g
0
1
/
1
100
1
1
/
2
50
2
1
/
4
25
3
1
/
8
12 .5
4
1
/
16
6.25
5
1
/
32
3.125
6
1
/
1
563
6
1
/
64
1
.
563
7
1
/
128
0.781
... ... ... n
1
/
2
n
100/(2
n
)

5. Heat production was twicethat of present-day at approximately
3 billion years ago, resulting in larger temperature gradients
within
the
Earth
larger
rates
of
mantle
convection
and
plate
within
the
Earth
,
larger
rates
of
mantle
convection
and
plate
tectonics
, allowing the production of igneous rocks such
askomatiites
thatarenotformedanymoretoday

6. Komatiite: It is a type ofultramafic
mantle-derived
volcanic rock
.
Komatiiteshavelowsilicon
,potassium
andaluminium
,andhighto
extremely
high
magnesium
content
Komatiite
was
named
for
its
extremely
high
magnesium
content
.
Komatiite
was
named
for
its
typelocality
alongtheKomatiRiver
inSouthAfrica
.

7. Much of the heatis created by decay of naturally radioactive
elements. An estimated45 to 90 percent of the heatescaping
from
the
Earth
originates
from
radioactive
decay
of
elements
from
the
Earth
originates
from
radioactive
decay
of
elements
mainlylocatedinthemantle Heat
was
retained
during
the
formation
of
the
earth
Heat
was
retained
during
the
formation
of
the
earth
Heat may be generated bytidal force
on the Earth as it rotates;
sincerock cannot flow as readil
y
as wate
r
it com
p
resses and
y
p
distorts,generatingheat.

8. In Earth'scontinental crust
,thedecayofnatural radioactive
isotopeshas had significant involvement in the origin of
geothermal
heat
geothermal
heat
.
Though the continental crust is composed of low density minerals
h
t
d
fld
bt
l
ti
iifi t
suc
h
as quar
t
zan
d
f
e
ld
spars
b
u
t
a
lso con
t
a
ins s
ign
ifi
can
t
concentrations of heavierlithophilic
minerals
such as uranium.
Because of this
,
it holds the lar
g
est
g
lobal reservoi
r
of radioactive
,
g
g
elementsfoundintheEarth
Litho-rock
Sidero-Iron
Chalco-Ore Atmo-Gas

9. Heat flows constantly from its sources within the Earth to the
surface by convection in the mantle and outer core, and by
conduction
from
the
surface
conduction
from
the
surface
.
Mean heat flow is
65 mW/m
2
overcontinental crust
and
101
mW
/m
2
over
oceanic
crust
But
is
101
mW
/m
2
over
oceanic
crust
.
But
is
much more concentrated in areas where
thermal energy is transported toward
the
crust
by
convection
such
as
the
crust
by
convection
such
as
alongmid-ocean ridges
andmantle
plumes

10. Most of the heat in the Earth is lostthrough plate tectonics,by
mantleupwellingassociatedwithmid-oceanridges.
The final major mode of heat loss is byconduction
through
thelithosphere
,themajority of which occurs in the oceansdue to
th
t
th
bi
h
thi
d
th
d
th
th
ecrus
t
th
ere
b
e
ing muc
h
thi
nner
an
d
younger
th
an un
d
e
r
th
e
continentsandcompositionallysuitable
forrapidheattransfer

11. PRESSURE
With every km in depth pressure increases by about 250 atmospheres
(One
atmosphere
=
14
7
lb/sq
in
the
average
atmospheres
.
(One
atmosphere
14
.
7
lb/sq
in
,
the
average
pressureoftheatmosphereatsealevel. The
pressure
in
the
Earth's
inner
core
is
slightly
higher
than
it
is
at
The
pressure
in
the
Earth's
inner
core
is
slightly
higher
than
it
is
at
the boundary between the outer and inner cores: it ranges from
about 330 to 360 gigapascals (3,300,000 to 3,600,000 atm).Iron
can be solid at such high temperatures only because its melting
temperatureincreasesdramaticallyatpressuresofthatmagnitude

12. PREM Model

13. GRAVITY
The first
p
erson to measure the
g
ravit
y
isGalileo. In his honou
r
,
p
gy
the unit of gravity is expressed in ‘gal’.1gal=10
-2
ms
-2
.The
gravitationalaccelerationattheearth’ssurfaceis981gal.
Gravity Gravity
 
Recovery 
and Climate 
Experiment
Earth's gravity measured by NASA'sGRACE
mission, showing
deviations from thetheoretical gravity
of an idealized smooth
Earth
the
so
-
called
earth
ellipsoid
Red
shows
the
areas
where
Earth
,
the
so
-
called
earth
ellipsoid
.
Red
shows
the
areas
where
gravity is stronger than the smooth, standard value, andblue
revealsareaswheregravityisweaker.

14. ‰Thegravity of Earth, denotedg, refers to
theacceleration
that theEarth
imparts to objects on or near
its
surface
its
surface
‰It has an approximate value of 9.81 m/s
2
, which means that,
ii
th
ff t
f
i
it
th
d
f
ignor
ing
th
ee
ff
ec
t
so
f
a
ir
res
is
t
ance
,
th
espee
d
o
f
an
objectfalling freely
near the Earth's surface will increase by
about9.81metres
p
e
r
secondever
y
second
p
y
‰The precise strength of Earth's gravity varies depending on
location
The
nominal
"
average
"
value
at
the
Earth
's
surface
location
.
The
nominal
average
value
at
the
Earths
surface
,
knownasstandardgravity
is,bydefinition,9.80665m/s
2
‰
A
perfect
sphere
of
spherically
uniform
density
(density
varies
‰
A
perfect
sphere
of
spherically
uniform
density
(density
varies
solely with distance from centre) would produce a gravitational
field of uniform magnitude at all points on its surface
, always
iti
di tl
td
th
h'
t
po
in
ti
ng
di
rec
tl
y
t
owar
d
s
th
esp
h
ere
'scen
t
re.

15. The reference gravity formula adopted by the international
Association of Geodesy in 1967 is:

16. ‰However, the Earth deviates slightly from this ideal, and there
are consequently slight deviations in both the magnitude and
direction
of
gravity
across
its
surface
Furthermore
the
net
direction
of
gravity
across
its
surface
.
Furthermore
,
the
net
force
exerted on an object due to the Earth, called "effective
gravity" or "apparent gravity", varies due to the presence of
th
ft
h
itil
t
th
Eth'
tti
A
o
th
e
r
f
ac
t
ors,suc
h
as
iner
ti
a
l
response
t
o
th
e
E
ar
th'
sro
t
a
ti
on.
A
scaleorplumbbob
measuresonlythiseffectivegravity.
‰Parameters affecting the apparent or actual strength of Earth's
gravity includelatitude
,altitude
, and the
local
topography
and
geology
local
topography
and
geology
.

17. VARIATION OF ‘g’ WITH LATITUDE
‰The surface of the Earth is rotating, so it is not an inertial frame
of
reference
At
Equator
the
outward
centrifugal
force
produced
of
reference
.
At
Equator
,
the
outward
centrifugal
force
produced
by Earth's rotation is larger than at pole. This counteracts the
Earth's gravity to a small degree – up to a maximum of 0.3% at
th
Et
d
d
th
t
dd
lti
th
e
E
qua
t
o
r
–
an
d
re
d
uces
th
eapparen
t
d
ownwar
d
acce
lera
ti
on
offallingobjects.
‰The second major reason for the difference in gravity at
different latitudes is that the Earth's e
q
uatorial bul
g
e
(
itself also
q
g
(
caused by inertia)causes objects at the Equator to be farther
fromtheplanet'scentrethanobjectsatthepoles.

18. ‰Because the force due to gravitational attraction between two
bodies (the Earth and the object being weighed) varies
inversely
with
the
square
of
the
distance
between
them
an
inversely
with
the
square
of
the
distance
between
them
,
an
object at the Equator experiences a weaker gravitational pull thananobjectatthepoles.
‰
I
bi ti
th
til
bl
d
th
ff t
f
th
‰
I
ncom
bi
na
ti
on,
th
e equa
t
or
ia
l
b
u
lge an
d
th
ee
ff
ec
t
so
f
th
e
Earth's inertia mean that sea-level gravitational acceleration
increases from about 9.780 m/s
−2
at the E
q
uato
r
to about
q
9.832 m/s
−2
at the poles, so an object will weigh about 0.5%
moreatthepolesthanattheEquator

19. VARIATION OF ‘g’ WITH ALTITUDE
‰Gravity decreases with altitude as one rises above the earth's
f
b
t
ltit d
t
di t
f
sur
f
ace
b
ecause grea
t
e
r
a
ltit
u
d
e means grea
t
e
r
di
s
t
ance
f
rom
theEarth'scenter
‰
A
ll othe
r
thin
g
sbein
g
equal, an increase in altitude from sea
g
g
level to 9,000 metres (30,000 ft) causes a weight decrease of about0.29%.

20. The following formula approximates the Earth's gravity variation
with altitude:
Where Where •g
h
is the gravitational acceleration at height h above sea level.
•r
e
is theEarth's mean radius
.
•g
0
is thestandard gravitational acceleration
.

21. GRAVITY VARIATION WITH DEPTH

23. VARIATION OF GRAVITY WITH LOCAL TOPOGRAPHY AND
GEOLOGY
Local variations intopography
(such as the presence of
mountains)andgeology
(such as the density of rocks in the
vicinity)cause fluctuations in the Earth's gravitational field, known
asgravitational anomalies
. Some of these anomalies can be very
extensive,
resulting
in
bulges
in
sea
level
,
and
extensive,
resulting
in
bulges
in
sea
level
,
and
throwingpendulum
clocksoutofsynchronisation.
The
fluctuations
are
measured
with
highly
sensitive
gravimeters
The
fluctuations
are
measured
with
highly
sensitive
gravimeters
,
the effect of topography and otherknown factors is subtracted,
and from the resulting data conclusions are drawn. Such
techniques are now used byprospectors
to findoil
andmineral
deposits
.Denser rocks (often containing mineralores
)cause
hi
g
h
er
t
h
a
nn
o
rm
a
ll
oca
l
g
r
a
vi
tat
io
n
a
lfi
e
lds
o
n
t
h
e
E
a
r
t
h'
s
su
rf
ace
.
ge
ta
oa
oca
ga tatoa
eds
o
te
at s
su ace
Lessdensesedimentaryrocks
causetheopposite.

24. OTHER FACTORS AFFECTING GRAVITY ON EARTH
In
air
objects
experience
a
supporting
buoyancy
force
which
In
air
,
objects
experience
a
supporting
buoyancy
force
which
reduces the apparent strength of gravity (as measured by an
object'sweight).
The gravitational effects of the Moon
and theSun
(also the cause
of thetides
)
have a ver
y
small effect on the a
pp
arent stren
g
th of
)
y
pp
g
Earth's gravity, depending on their relative positions; typical
variationsare2µm/s
2
(0.2mGal
)overthecourseofaday.
The final gravity value is expressed after many corrections, such as
Free
air
correction
Bouger
correction
Terrain
correction
as
Free
air
correction
,
Bouger
correction
,
Terrain
correction
,
TopographiccorrectionandLatitudecorrectionetc

25. Thegeoidis the shape that the surface of the oceans would take under the influence of Earth
's
gravitation
and
rotation
alone
in
the
absence
of
other
influences
such
as
winds
and
Earth s
gravitation
and
rotation
alone
,
in
the
absence
of
other
influences
such
as
winds
and
tides. All points on that surface have the samescalar potential
—there is no difference
inpotential energy
between any two.
Specifically,
the
geoid
is
the
equipotential
surface
that
would
coincide
with
the
mean
ocean
Specifically,
the
geoid
is
the
equipotential
surface
that
would
coincide
with
the
mean
ocean
surface of the Earth if the oceans and atmosphere were in equilibrium, at rest relative to the
rotating Earth,
The
surface
of
the
geoid
is
higher
than
the
reference
ellipsoid
wherever
there
is
a
positive
The
surface
of
the
geoid
is
higher
than
the
reference
ellipsoid
wherever
there
is
a
positive
gravity anomaly (mass excess) and lower than the reference ellipsoid wherever there is a negative gravity anomaly (mass deficit).
[2]
The differences in gravity, and hence the scalar
potential field, arise from the uneven distribution of massin the Earth.

26. Variations in the height of the geoidal surface are related to density anomalous distributions
within the Earth. Geoid measures help thus to understand the internal structure of the planet.
Synthetic calculations show that the geoidal signature of a thickened crust (for example, in
orogenic
belts
produced
by
continental
collision
)
is
positive
opposite
to
what
should
be
in
orogenic
belts
produced
by
continental
collision
)
is
positive
,
opposite
to
what
should
be
expected if the thickening affects the entire lithosphere
.