Geoscience Reference
In-Depth Information
What are the Patterns and Drivers in Extinction and Recovery?
The record of life on Earth is punctuated by a series of mass extinctions,
including the so-called Big 5—Ordovician-Silurian, Late Devonian, end-Permian,
end-Triassic, and Cretaceous-Paleogene (often called K-T)—as well as major biotic
reorganization events such as the Paleocene-Eocene-Thermal Maximum (PETM).
The committee's view of these extinctions and recovery has in the past been strongly
dominated by records of taxonomic change (e.g., Raup and Sepkoski, 1984). But this
is changing, with greater emphasis on other kinds of diversity that may have at least
as much impact on function in ecosystems and the biosphere as a whole. Important
approaches include analysis of morphological and physiological disparity, biotic
provinciality, and the role of biodiversity in functional (and ecological) redundancy
and ecosystem stability.
Box 2.7
Molecular Geobiology Data Revolution
Armed with modern capabilities in macromolecular sequencing, the structures and
processes of entire microbial communities can now be characterized. New advances allow
determination of tens of billions of bases per run, and this scale of capacity is jump-starting
the field of environmental genomics. Genomic data derived from environmental RNA reveal
microbial dynamics on scales of minutes, while data derived from DNA allow characterization
of geobiological evolution over billions of years. The field is poised to address challenges
facing humanity, including increasing soil fertility to aid in feeding the world's growing
population, providing novel approaches to managing Earth's resources and waste disposal
and attenuating the impacts from human land use and climate change in the critical zone.
This emerging revolution offers unprecedented insight into the microbial communities
that mediate Earth's elemental cycles. With our growing ability to identify the biological
diversity of microbes irrespective of whether they can be cultivated, it can now be identified
where these microbes are located in relation to each other and to Earth materials, and their
activity and geochemical roles can be tracked over space and time. Never before has it been
possible to obtain such information without having microbes in culture, and never before have
so many data been collected. But this is just the tip of an immense “iceberg” in a data
revolution that is beginning to show its full weight, as the “meta-omics” world (meta-
genomics, proteomics, transcriptomics) becomes readily accessible. The availability of
inexpensive sequencing has moved studies at the interface between geochemistry and
molecular biology to a new level. Nearly limitless amounts of molecular (sequence) data can
now be collected, allowing the genetic complement of nearly any environment to be seen
nearly instantaneously. Billions of base pairs can be “harvested” and analyzed to provide a
DNA snapshot of the biodiversity and gene diversity of an environment, while monitoring of
RNA and protein expression provides new avenues for probing geobiological dynamics in
near real time. From this perspective come unprecedented baselines and records of change
in the face of recent environmental perturbation.
Accompanying these extraordinary opportunities is the reality that we still have a long
way to go to realize the promises that new “omics” approaches hold for transforming the
fields of geobiology and geochemistry. The explosion in sequencing has unveiled staggering
genetic diversity, but these new vistas are matched by a widening gap between gene
sequencing data and our understanding of the data's biochemical, ecological, and
geochemical function. Much critical and fundamental work is needed, including (1) annotating
and identifying new genes, (2) sorting out the implications of genetic diversity within microbial
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