Introduction - The Solid Earth - page 2

Figure 1.1. The major
internal divisions of the
Earth.

CRUST

Lithosphere

Transition
zone

MANTLE

solid

(Mg, Fe)
silicate

D ′′ layer

OUTER
CORE

liquid

Fe with
Ni, O, S
impurities

INNER
CORE

solid

Fe

Mohorovici´cin1909,istermed the Mohorovicic discontinuity, or Moho for short.
The core of the Earth was discovered by R. D. Oldham in 1906 and correctly delin-
eated by Beno Gutenberg in 1912 from studies of earthquake data (Gutenberg
1913, 1914). The core is totally different, both physically and chemically, from
the crust and mantle. It is predominantly iron with lesser amounts of other ele-
ments. The core was established as being fluid in 1926 as the result of work on
tides by Sir Harold Jeffreys. In 1929 a large earthquake occurred near Buller in
the South Island of New Zealand. This, being conveniently on the other side of the
Earth from Europe, enabled Inge Lehmann, a Danish seismologist, to study
the energy that had passed through the core. In 1936, on the basis of data from
this earthquake, she was able to show that the Earth has an inner core within the
liquid outer core. The inner core is solid.
The presence of ancient beaches and fossils of sea creatures in mountains
thousands of feet above sea level was a puzzle and a stimulation to geologists
from Pliny's time to the days of Leonardo and Hutton. On 20 February 1835, the
young Charles Darwin was on shore resting in a wood near Valdivia, Chile, when
suddenly the ground shook. In his journal The Voyage of the Beagle Darwin (1845)
wrote that 'The earth, the very emblem of solidity, has moved beneath our feet