Geoscience Reference
In-Depth Information
have accumulated in the ancient deep sea. Indeed, we have geological
evidence for this in the massive accumulation of a peculiar type of sedi-
mentary rock known as banded iron formations (BIFs) (
plate 3)
. hese
types of rocks are particularly abundant in the rock record before about
2.5 billion years ago (we'll hear much more about BIFs in later chap-
ters), and our best models argue that these BIFs formed from ferrous
iron dissolved in seawater. But focusing again on the particle layer, what
is the source of all these bacteria, and the rust?
The microbiologist Fritz Widdel from the Max Planck Institute for
Marine Microbiology in Bremen, Germany, is the picture of patience.
Indeed, this patience has allowed him to make many fundamental
breakthroughs in our understanding of microbial metabolism. In one
of these breakthroughs, Fritz and his students collected mud from a
drainage ditch near the Max Planck Institute,
12
and incubated it in the
light with added ferrous iron. They waited and waited and waited, and
eventually, after some months, they saw a population of purplish bac-
teria growing on the mud. They transferred these bacteria to new media,
and waited some more. Then finally, after the waiting was done, they
had isolated a population of anoxygenic phototrophic bacteria (
plate 4)
able to grow from the ferrous iron and forming, essentially, rust in the
process. People had long suspected that such a population might exist
in nature, but no one had either Fritz's patience or talent to isolate
them. But, would such a population have been of importance in the
ancient oceans?
As students of the distant past, we try to identify modern environ-
ments that resemble, as closely as possible, the ancient environments we
seek to understand. here, though, might we ind an analog to a three
to four billion-year-old iron-rich ocean? hile I was pondering this,
a PhD student from Canada, Sean Crowe, was visiting our lab and ex-
plained that he was working on Lake Matano, Sulawesi, Indonesia.
This turns out to be just such an environment. The lake is deep, almost
600 m, clear and stable. Critically, it accumulates substantial concentra-
tions of ferrous iron in the bottom waters. Sean was planning another
trip to Matano and invited my PhD student CarriAyne Jones to join.
Sean and CarriAyne learned much about the lake, but critically, they
discovered an anoxygenic phototrophic population just where iron,
