SCIENCE magazine editors' choice
(NOTE: The following is directly quoted from the "Editors' Choice" of the
SCIENCE magazine.  One thing has to be clarify here, i.e., the Archaea and
the Bacteria are two different domains of life (the third domain is the Eukaria).
This paper is talking about the Archaea, not the Bacteria, neither "Archean
bacteria".  Dr. Ming)
GEOCHEMISTRY: Shielding Bacteria
Linda Rowan

Archean bacteria living about 2.5 billion years ago needed to be able to
withstand high levels of UV irradiation because of the lack of atmospheric
oxygen as a UV screen. Many early bacteria may have survived in a deep
marine environment where the water provided UV shielding. However, there is
evidence in the geological record of microbial mats and stromalites that
inhabited shallow water environments, which would require some other means
of UV protection.

Phoenix et al. placed cultures of cyanobacteria isolated from the Krisuvik
hot springs, Iceland, in a silicon- and iron-rich solution. Rims of iron-
enriched silica formed around the cells, and the cultures were then exposed
to UV irradiation. Cells continued to grow within the mineralized rims even
under intense UV. Thus, biomineralization may have helped the simplest
forms of life to thrive in the intense sunshine of the Archean. -- LR

Geology 29, 823 (2001).