Chemistry Reference
In-Depth Information
With this RiMG review, the foremost goal of the authors is to create a volume focused
upon topics essential for scientists, and in particular earth scientists, entering the field. With
this objective in mind, our approach is first to establish relevant aspects of molecular
biology and protein chemistry (e.g., Evans 2003) and then the thermodynamic principles
necessary for mineralization to occur (e.g., De Yoreo and Vekilov 2003). Equipped with
this toolbox of essentials and Nature as our guide, we examine in some detail six major
biomineralization processes. As much as possible, we attempt to de-emphasize specifics
unique to some organisms and, instead focus on the major mineralizing strategies.
Fundamental to this approach is an evolutionary perspective of the field. It is noteworthy
that underlying mechanisms for controlling the biomineralization processes appear to be
used again and again by members of many phyla.
The last part of this volume examines views of how biomineralization processes have
been employed by organisms over Earth history and their intertwined relations to earth
environments. By considering the impacts of these relations upon global biogeochemical
cycles, studying the temporal and geochemical results of mineral-sequestering activities,
and asking critical questions about the topic, we can arrive at a deeper understanding of
biological mineralization and of life on earth.
This chapter
This introductory chapter is divided into two main sections: an overview of basic
biomineralization strategies and processes and a discussion of how understanding more
about biomineralization mechanisms may shed light on the manner in which environmental
signals may or may not be embedded in the minerals produced by organisms.
Despite the fact that the hallmark of biomineralization is the control that organisms
exert over the mineralization process, it has been noted by earth scientists for the last 50
years that biologically produced minerals often contain embedded within their
compositions, signatures that reflect the external environment in which the animal lived.
Thus many geochemists have focused on extracting the signal for past seawater
temperatures, salinities, productivities, extent of sea water saturation, and more. The task
has not been an easy one! In many cases, the control processes either completely
eliminate the signals or shift them. Sorting out this so-called vital effect (Urey 1951) or
physiological effect (Epstein et al. 1951) from the environmental signal remains a
problem yet to be solved. In the second part of this chapter, we will discuss some of the
principles of mineralization in terms of the vital effect—a subject of much current
interest to the earth sciences community.
OVERVIEW OF BIOMINERALS
Over the last 3500 Myr or so, first prokaryotes and then eukaryotes developed the
ability to form minerals. At the end of the Precambrian, and in particular at the base of
the Cambrian some 540 Myr ago, organisms from many different phyla evolved the
ability to form many of the 64 different minerals known to date (e.g., Knoll 2003). While
the names and corresponding chemical compositions of minerals produced by organisms
are given in Table 1 (Weiner and Addadi 2002), this list is unlikely to be complete, as
new biologically produced minerals continue to be discovered.
What is a biomineral?
The term biomineral refers not only to a mineral produced by organisms, but also to the
fact that almost all of these mineralized products are composite materials comprised of both
mineral and organic components. Furthermore, having formed under controlled conditions,
biomineral phases often have properties such as shape, size, crystallinity, isotopic and trace
