Geoscience Reference
In-Depth Information
100,000,000
10,000,000
1,000,000
100,000
sedimentary rocks
10,000
1,000
1
10
100
1,000
Age (millions of years)
Figure 9.1. the area of exposed sedimentary rocks as a function of geologic age. the steep
drop-off with time partly indicates the burial of rocks into earth's crust; however, over long
time scales, loss by weathering and erosion is probably the most important cause of the
drop-off. From data kindly supplied by Bruce wilkinson (see wilkinson et al. 2009).
This is because through time, they have had a higher probability of
being delivered to the zone of weathering at the Earth surface. Indeed,
if you make a tally of all the rocks you can find on the Earth surface and
group them into ages, you find that the abundance of rocks decreases as
age increases (
ig. 9.1)
. If you try to quantify this effect, about half of the
rocks remaining from any time in Earth history will disappear through
weathering (though some are buried in the crust) over a time scale of
about 200 to 300 million years. This is approximately the same length of
time as the Lomagundi isotope event, and I think it makes sense that
the duration of the event could have been limited by the availability of
old Archean rocks and the availability of recycled organic matter and
nutrients. To be sure, this is all just speculation, but I would bet that
the Lomagundi event will be the focus of intense scrutiny over the next
few years, and I will be surprised if Holland's initial instinct, that it is
related in some way to the GOE, is proven incorrect.
So, the GOE appears to have been followed by a massive burial of
organic carbon as expressed in the Lomagundi isotope event. Dick Hol-
land and his former postdoc Andrey Bekker have argued that the Loma-
