Geoscience Reference
In-Depth Information
13
C
Carbonate
δ
-15
-10
-5
0
5
10
3000
Biological activity
3200
550 Ma
3400
3600
3800
Gaskiers
590 Ma
glaciation
4000
4200
635 Ma
4400
Figure 9.11
13
C values after the Gaskiers glaciation in Oman (data from Fike
et al.
,
Negative excursion of
δ
≈
635 Ma). The Gieskes
glaciation (
590 Ma) locally misses diamictites but can be recognized with the cap-carbonates in
the middle of the section. The
≈
13
C values lower than those of the mantle indicate that a carbon
reservoir rich in
12
C, possibly gas hydrates, was being oxidized. Oxidation coincides with the
radiation of multicellular organisms (Metazoan).
δ
As previously alluded to, oxidation of the ocean also resulted in the oxidation of oceanic
sulfur into sulfate, which clearly shows in the burial of pyrite with negative
34
S values
(
Fig. 9.10
). The reason why such a massive rise of oxygen in the atmosphere and the ocean
took place remains so far poorly understood.
δ
9.3 The geochemical environment of the origin of life
In a famous experiment, Miller and Urey
(1959)
triggered electrical discharges in a balloon
containing ammonia, methane, and liquid water. After a few hours, the solution became
very rich in amino acids, which are the building blocks of proteins. After first being hailed
as a breakthrough illuminating our understanding of the origin of life, this experiment was
heavily criticized for misrepresenting the early Earth atmosphere, which, critics said, was
