Earth internal structure

1. The Earth’s Interior
Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)

2. Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)
100–400 billion stars and
more than 100 billion planets.
Scientists estimate that there
may be tens of billions of solar
systems in our galaxy, perhaps
even as many as 100 billion.

3. Earth
Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)

4. Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)
• Four different layers form from original mixture
Differentiation of early Earth:

5. The Earth’s Interior
Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)

6. The Earth’s Interior
Oceanic crust:
Thickness: 10 km
Composition: Basaltic (Dark)
Age: Up to 200 million years old
Density: 3.0 g/cm3
Continental Crust:
Thickness: 20-90 km (average ~35 km)
Composition: Granitic (Light)
Age: Recent to 4.6 billion years old
Density: 2.7 g/cm3
Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)
Crust

7. The Earth’s Interior
Mantle:
Peridotite (ultramafic)
Upper Mantle to 410 km (olivine  spinel)
 Low Velocity Layer 60-220 km
Transition Zone as velocity increases ~ rapidly
 660 spinel  perovskite-type
Lower Mantle has more gradual
velocity increase
Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)

8. The Earth’s Interior
Core:
Fe-Ni metallic alloy
Outer Core is liquid
 No S-waves
Inner Core is solid
Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)

9. Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)

10. Thickest part of the crust…. Narrowest part of the crust….
Himalaya Marianas trench
Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)

11. Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)
OCEANIC CRUST IS YOUNG GEOLOGICALLY!!! CONTINENTAL CRUST IS BUOYANT AND OLD

12.  Mantle convection is the slow creeping motion of Earth's solid silicate mantle caused by convection
currents carrying heat from the interior to the planet's surface.
Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)

13. Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)

14. Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)

15. The Earth’s Interior
Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)
• How do we know about the earth interior???
 Drilling (up to 5/6km)

16.  Drilling
• Wells drilled into Earth are mostly in the upper 7 km of the crust
• Deepest well = Soviet (Russian) well in northern Kola Peninsula 4 year
effort to drill a 12 km (12,000 m) hole, starting in 1970.
• Deepest U.S. well was a gas well drilled in Oklahoma. Drilling starting
in 1974 and stopped at 31,441 ft (9,583 m or 9.58 km) when it struck
molten sulfur.
• Germans drilled 3.5 km pilot hole and found bottom temperature was
118 º C (instead of the expected 80 º C)
 Volcanic activity
• Materials are brought up from below. Xenoliths = foreign rock (pieces
of the mantle in lava); example: coarse-grained olivine (peridotite)
xenoliths in basaltic lava. Only useful to depth of about 200 km
 High pressure laboratory experiments
 Samples of the solar system (meteorites)
 Study of seismic waves generated by earthquakes and nuclear explosions
Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)

17. The Earth’s Interior
P-Wave: Can Travel Both
through solid and liquid
S-Wave: Travel only through
the Solid
Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)
 By seismic waves analysis
Earthquake clues - Earthquake energy
transmitted as seismic waves that
pass through Earth. Seismic waves
have been used to probe the interior.
Wave velocity changes with density
Velocity changes give depth of layer
changes.

18. Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)

19. Division Thickness Composition
Inner core 1216 km solid iron-nickel alloy
Outer core 2270 km liquid iron-nickel alloy
Mantle 2885 km
solid Fe-Mg rich rock (high density-
silicate)
lower mantle -- high density and
ductile
upper mantle - intermediate density
and brittle
Crust 5-10 km continental crust - brittle, low
density, Fe-Mg poor rock
25-70 km oceanic crust - brittle, higher density,
Fe-Mg rich rock
Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)

20. Elements that build the Earth
Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)

21. Homework
 Make a handout regarding earth interior. It must be completed by considering the following topics:
Md. Yousuf Gazi, Lecturer, Department of Geology, University of Dhaka (yousuf.geo@du.ac.bd)
• Detail description of oceanic and continental crust, mantle, and core
• How do we know about the earth interior?
• Mantle convection cell