Properties of the Earth
I. Density
- A. Density is the mass divided by the volume; d = m/v
- B. Density of the Earth is about 5.5 g/cm3
- 1. This is not uniform
- 2. By comparison, the density of water is 1.0 g/cm3
II. Internal
structure
- A. determined
from seismology: reflection of earthquake waves
- 1. P-waves (primary or "push"; compressional) : faster
- 2. S-waves (secondary or "shake"; shear) : slower, cannot go
through liquid
- B.
discontinuities in the paths of seismic waves indicate layering
|
Density |
% volume |
% mass |
| 1. crust: |
2.0-3.5 g/cm3 |
2% |
<1% |
| 2. mantle: |
3.5-5.0 g/cm3 |
82% |
68% |
| 3. core: |
~10.8 g/cm3 |
16% |
32% |
- C. We know
something about the internal composition because of meteorites
(meteorites are rocks on Earth derived from outside Earth)
- 1. Iron meteorites (metallic Fe minerals); similar to core
material
- 2. Stony meteorites
- i. Achondrites (do not contain chondrules); similar to
mantle & crust material)
- ii. Chondrites (contain chondrules, silicate minerals in
the shape of spherules); primitive planetary material
- D. The eight
most common elements in Earth's crust
| Element |
Symbol |
% by weight |
% by volume |
| Oxygen |
O |
46.6 |
93.8 |
| Silicon |
Si |
27.7 |
0.9 |
| Aluminum |
Al |
8.1 |
0.8 |
| Iron |
Fe |
5.0 |
0.5 |
| Calcium |
Ca |
3.6 |
1.0 |
| Sodium |
Na |
2.8 |
1.2 |
| Potassium |
K |
2.6 |
1.5 |
| Magnesium |
Mg |
2.1 |
0.3 |
| All other elements |
|
1.5 |
-- |
- E. Sources
of heat in the earth
- 1.
Geothermal gradient
- 2.
Radioactive heat from decay of radioactive uranium, thorium, and
potassium
Last update 2/22/2005
Webpage designed by Hiram Jackson.
Contact Geology webmanager, Hiram Jackson, at jacksoh@crc.losrios.edu