Geology Reference
In-Depth Information
10
12
H
R.E.E.
10
10
He
10
10
8
Ce
Nd
O
1
C
Dy
Sm
Gd
Er
Yb
La
Si
Fe
10
6
10
-1
Pr
Eu
Tb
(Pm)
Ho
Tm
Lu
10
4
55
60
65
70
Even Z
10
2
Li
Pb
odd Z
B
1
Be
Th
U
10
-2
0
10
20
30
40
50
60
70
80
90
Atomic number
Z
Figure 11.2
The composite Solar-System elemental abundance curve. The vertical axis shows on a
logarithm
ic scale the
number of atoms of each element per 10
6
atoms of silicon. The inset shows abundances of the rare earth elements ('REE',
La to Lu) and some neighbouring elements. The element promethium (Pm) has no stable isotopes and is not found in
meteorites (see Exercise 11.1 at the end of this chapter). ○, elements with Z even;
●
, elements with Z odd. The stippled
band emphasizes the abundance difference between even-Z and odd-Z nuclides.
(e) The general decline in abundance as
Z
increases
(item (b)) is interrupted by a sizable peak around
Z
= 26, comprising elements in the neighbourhood
of iron.
1993, Ferreira, 2006). Baryonic matter began to take
form in the expanding primordial fireball after only
the first second of time, at a temperature of about 10
billion degrees (10
10
K). Furthermore, theory predicts
that 75% of the baryons formed were protons and
25% neutrons. After about 15 seconds of cooling,
when the temperature of the fireball had fallen below
3 × 10
9
K, neutrons combined with protons to form a
sprinkling of light nuclei such as
2
H (deuterium),
3
He,
4
He and
7
Li. But it was far too hot for these nuclei to
capture electrons at this stage: matter in the universe
had to wait 100,000 years or more before the temper-
ature of the expanding cosmos had fallen low enough
(to about 5 × 10
3
K) for neutral atoms of these light
nuclides to form.
Why is temperature such a key factor here? The
kinetic energy of any atomic particle increases with
temperature. The electrostatic force binding an
These features provide clues as to how the elements
were formed.
Cosmic element production
The Hot Big Bang
Modern cosmology is founded on the standard model
of the Hot Big Bang, an event that occurred 13.8 Ga
ago whose early moments have been illuminated in
astonishing detail by the application of theoretical
astrophysics (Weinberg, 1993; Riordan and Schramm,
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