solar system

1. The Earth in the Solar System

2. Solar System Formation
 To understand the composition and early evolution of the Earth it is necessary
to consider as far back as the formation of our solar system.
 Solar system formation was a complex process that is not well understood
because of the lack of data and the vast physical and chemical complexities of
the process.
 However, there are certain key parameters that we do know, we know from the
study of meteorites the age of the solar system and its initial composition, and
comparatively we know much about the nature of the present-day solar system.

3. Solar System Formation cont.
 In addition, we have observations of old and young stars that inform us about
the life cycle of the sun.
 The goal is to use all the information in combination with the laws of physics
and chemistry to fill in the blanks between the initial state and the present state
of the solar system, and to consider what this means for the constitution and
initial state of the Earth.

4. Rotation and Angular Momentum
 All the planets revolve in the same direction around the sun, and in practically the same
plane.
 For the most part they also rotate in the same direction about their own axes, although there
are notable exceptions, such as Venus.
 The gravitational collapse of molecular clouds is widely believed to lead to star formation
and our solar system likely condensed from a collapsed, rotating cloud of gas and dust.
 In a rotating protostar the gravitational attraction everywhere will be towards the center of
mass. But the centrifugal force will be directed normal to the axis of rotation. The resolved
force vector will move gas and dust nearer to the median plane as the cloud contracts.

5. Rotation and Angular Momentum
 One of the more interesting boundary conditions is the present distribution of angular
momentum.
 Consider a planet of mass m that orbits a central body of mass M, whose position with
respect to the central body can be described by a vector r.
 The orbital angular momentum (L) of the planet can be written
 where r is distance, m is the mass, ω is the angular velocity (=dθ/dt), and θ is the angle with
respect to a fixed direction in the orbit plane.

6. Rotation and Angular Momentum
 One of the more interesting boundary conditions is the present distribution of angular
momentum.
 Consider a planet of mass m that orbits a central body of mass M, whose position with
respect to the central body can be described by a vector r.
 The orbital angular momentum (L) of the planet can be written
 where r is distance, m is the mass, ω is the angular velocity (=dθ/dt), and θ is the angle with
respect to a fixed direction in the orbit plane.

7. THE SUN
 Geophysics does not talk to us in geological terms and we have to interpret
obtained physical parameters in a geological sense.
 The successful interpretation is based on experiences of an interpreter and on
the a priori knowledge of the geological environment studied.
 For example; if we know that we are working in the crystalline complex we
can mostly likely leave sedimentary rocks out of our interpretation and we are
left with rhyolite, phonolite, andesite, granite or schist..

8. Geophysics Cont.
 The advantage of geophysics is that it is able to image hidden structures and
features inaccessible to direct observation and inspection.
 That from measurements on the surface we can deduce what is in the depth.
 Compare this with a geological mapping where we study the outcrops and, if
we are lucky, have also a few trenches or boreholes.
 There we have just a surface situation and we can only guess how the surface
structures continues to the depth.

9. Geophysics Cont.
 In this Figure From the surface geological mapping we would
see a sediment filled valley with inclined strata on both sides.
 However, we have no clue what it looks like in depth.
 Four possibilities are sketched in the figure.
 The surface geological mapping cannot give us any hint which
of these is correct unless we make a line of boreholes.
 This, of course, would be both – time-consuming and
extremely expensive.
 With geophysics, the differences can be deduced.

10. Geophysics Cont.
 The use of physics to study the interior of the Earth, from land surface to the
inner core is known as Solid Earth Geophysics. Solid Earth Geophysics can be
subdivided into Global Geophysics or pure Geophysics and Applied
Geophysics.

11. Geophysics Cont.
 Global Geophysics is the study of the whole or substantial parts of the planet.
Geophysical methods may be applied to a wide range of investigations from;
studies of the entire earth to exploration of a localized region of the upper
crust, such as plate tectonics, heat flow, and paleomagnetism.
 Applied Geophysics is the study of the Earth’s crust and near surface to
achieve an economic aim, or making and interpreting measurements of
physical properties of the earth to determine subsurface conditions usually
with an economic objectives ( e.g. Discovery of fuel or mineral deposits).

12. Geophysics Cont.
 Applied Geophysics Comprises the following subjects:
1. Determination of the thickness of the crust (which is important in
hydrocarbon exploration.
2. Study of shallow structures for engineering site investigations.
3. Exploration for groundwater and minerals and other economic resources.
4. Trying to locate narrow mine shafts or other forms of buried cavities.
5. The mapping of archaeological remains.
6. Locating buried piper and cables

13. HISTORY OF GEOPHYSICS
 The beginning of geophysics started since Gilbert’s discovery which stated that the
earth behaves as a great and irregular magnet and Newton’s theory of gravitation.
 The initial step in the application of geophysics to the search for minerals was taken in
1843 by Von Warde, he used the magnetic theodolite of Lamont to discover
magnetic ore bodies.
 In 1879 a book by Robert Thalen was published entitled “On the Examination of iron
ore deposits by magnetic methods".
 At that time, the first magnetometer called Thalen Tiberg magnetometer was
manufactured in Sweden.

14. HISTORY OF GEOPHYSICS cont.
 During the past seventy years, geophysics was used greatly in oil and gas
exploration and many geophysical techniques have been developed for the
detection and mapping of unseen deposits and structures.
 Advances have been rapid during the past decade because of the development of
new electronic devices for field equipment and the widespread applications of the
digital computer in the interpretation of geophysical data.
 Several of the devices now used by geophysicists were developed from methods
used for locating guns, submarines and aircraft during the two world wars.

15. RELATION BETWEEN GEOLOGY AND GEOPHYSICS:
 Geology involves the study of the earth by direct observations on rocks either
from surface exposures or from boreholes and the deduction of its structures,
composition and historical evolution by analysis of such observations.
 Geophysics involves the study of the inaccessible earth by means of physical
measurements, usually on or above the ground surface. It also includes
interpretation of the measurements in terms of subsurface structures and
phenomena.

16. GEOPHYSICAL METHODS
 The physical properties of rocks (Density, Magnetic susceptibility,
Elasticity, Electrical resistively or conductivity, Radioactivity,
Thermal conductivity) have been used to devise geophysical
methods that are essential in the search for minerals, oil, and gas
and other geological and environmental problems.

17. GEOPHYSICAL METHODS cont.
 These methods are;
1- Gravity method (Gravimetry)
2- Magnetic method (Magnometry)
3- Electrical method (Geoelectrical)
4- Seismic method (Seismology)
5- Electromagnetic method
6- Geothermal method
7- Radiometric method

18. GEOPHYSICAL METHODS cont.
 These methods can be classified into two distinct types:
1- Passive methods
 Which detect variations within the natural fields associated with the earth, like the
gravitational and magnetic fields, such as gravity, magnetic, some electric and some
electromagnetic methods, radioactive, and geothermal methods.
2- Active methods
 These artificially generated signals transmitted into the ground and then modify the
received signals in ways that are characteristic of the materials through which they travel.
Examples of these methods are seismic and some electrical methods.

19. GEOPHYSICAL METHODS cont.
 Generally, natural field methods (passive methods) can provide information on earth
properties to greater depths and are simpler to carry out than artificial source methods
(active methods).
 Moreover, the artificial source methods are capable of producing a more detailed and
better resolved picture of the subsurface geology.

20. GEOPHYSICAL METHODS cont.
 The various geophysical methods depend on different physical properties.
 For example: gravity methods are sensitive to density contrasts within the sub-
surface geology and so are ideal for exploring for major sedimentary basins where
there is a large density contrast between the lighter sediments and the denser
underlying rocks.
 It would be inappropriate to use gravity methods to search for ground water where
there is a negligible density contrast between the saturated and unsaturated rocks.

21. GEOPHYSICAL METHODS cont.
 The basic geophysical methods are
listed below with the physical
properties to which they relate and their
main uses.

22. Applications:
1. Hydrocarbon exploration (coal, gas, oil)
2. Regional geological studies (over areas of 100s of km2 )
3. Exploration of mineral deposits.
4. Engineering site investigation.
5. Hydrogeological investigation.
6. Detection of subsurface cavities.
7. Mapping of leachate and contaminant plumes.
8. Location and definition of buried metallic objects.
9. Archaeo-geophysics.

23.  Geophysical methods are often used in combination. For example:
 The search for metalliferous mineral deposits often utilizes airborne magnetic and
electromagnetic surveying.
 Also prospecting for oil usually includes gravity, magnetic and seismic surveying.
 The importance of such combination appears in the interpretation stage, ambiguity
arising from the results of one survey method may be removed by consideration of
results from a second survey method.