Science Opportunities - Basic Research Opportunities in Earth Science - page 40

possibly present at least 2.7 billion years ago, 500 million to 600 million years
earlier than the oldest known eukaryotic fossils.
The discovery that most living animals share the same core set of
developmental genes has begun to make it possible to understand the genetic
basis for the differences between animals. Integration of these genetic data with
new morphological and geochronologic data from the fossil record allows
unraveling of the evolutionary events that led to novel morphologies, from the
earliest multicellular animals to the origin of flowers and the vertebrate skull.
This offers the opportunity for understanding key events, such as the Cambrian
explosion of multicellular animals ( Figure 2.6 ) and the mid-Paleozoic invasion
of land. Geological and molecular data can also be used to calibrate molecular
clocks based on differences between the DNA of living species; these clocks can
then be applied to lineages otherwise lacking a rich fossil record.
Discoveries of entirely new microbial organisms in ecologically and
geologically extreme environments (extremophiles) have greatly broadened the
concept of the versatility of life; microorganisms have been found kilometers
deep in Antarctic ice, in active vents along midocean ridges, and in fluids with a
pH of zero. Subduction zones likely contain the Earth's deepest biota, sustained
by energy from chemical redox reactions rather than solar radiation.
Studies of organic reactions on mineral surfaces have led to a new
understanding of how key prebiotic compounds were formed early in Earth
history. Molecules such as thioesters and acetic acid have been created under
geochemical conditions relevant to the early Earth, and nucleotides and amino
acids have been polymerized, providing possible clues to the origin of life.
Evolutionary Innovations
One of the most striking paleontological observations has been the uneven
distribution of evolutionary innovations in time and space. Pulses of innovation
following extinction events, such as the early Cenozoic radiation of mammals
following the extinction of dinosaurs and other Mesozoic dominants, are now
recognized as a crucial component of the evolutionary dynamic and are the focus
of a major new research direction linking paleobiologists, evolutionary
biologists, and ecologists. Evolutionary innovation also has a strong spatial
component, with major novelties appearing in disturbed environments, both on
land and in the sea, and in tropical latitudes. Recoveries from extinction events
and diversifications show significantly different trajectories in different regions
that sum to lasting effects on the global biota ( Figure 2.7 ).