Geoscience Reference
In-Depth Information
a clever, but somewhat indirect line of reasoning, the presence of sterols
means the presence of oxygen and therefore, the presence of cyanobac-
teria. It seems, then, that Jake (together with Roger and others involved
in the study) has found evidence for cyanobacterial production of oxy-
gen at least as far back as 2.67 billion years ago. At last, something we
can hang our hat on. Well, probably. The fly in this ointment is whether,
despite their great care, the biomarkers in Jake's rocks still represent
contamination. Jochen Brochs, a former student of Roger's now at The
Australian National University in Canberra, maintains that they most
probably do. Time will certainly tell.
This quest for cyanobacteria has had some dizzying heights, some
depressing lows, and it ends with a strong dash of realism. The problem
is hard. The rocks aren't in good shape, and there aren't many of them.
That's just the way it is. It doesn't mean, however, that people will stop
looking. Perhaps a big ind—maybe beautifully preserved 3.5-billion-
year-old cyanobacterial cells lie somewhere underground, just out of
reach, to be exposed by chance or design by some curious scientist
in the future. Or maybe some other clever method will be developed to
look for cyanobacteria. Indeed, that's partly what the next chapter is
about. We will look at the chemistry of early Earth and see if we can use
chemical approaches to uncover any signs of oxygen.
