Biology Reference
In-Depth Information
So What's the Problem?
Would there not also be some glory for man to know how to burst the limits of time,
and, by observations, to recover the history of this world, and the succession of
events that preceded the birth of the human species?
—GEORGES CUVIER,
1812, quoted in Martin Rudwick,
Bursting the Limits of Time
, 2005
Seldom has a single discovery in chemistry had such an impact on the thinking of
so many fi elds of human endeavor. Seldom has a single discovery generated such
wide public interest.
THOMAS HIGHAM,
quoted in Royal Ervin Taylor,
Radiocarbon Dating
, 1987
Challenges to the reliability of absolute dates were almost a foregone con-
clusion exactly because the results do impinge on human endeavors and
public interest. The origin of the universe around 15 billion years ago
was based initially on a theoretical and now on a documented expanding
universe—the expansion documented, for example, by 1992 data from the
Cosmic Background Explorer Satellite launched in 1989 and by observa-
tions and analysis of the density and distribution of ionized particles from
the Hubble Telescope. Lead-uranium ratios and fi ssion-track dating both
indicate the Earth formed about 4.5 billion years ago and that life appeared
about 3.5 billion years ago (Knoll 2004; Szostak 2009; Powner et al. 2009;
Whitfi eld 2009). The latter is deduced from the presence of structurally
preserved fossils, biogenetic deposits (e.g., stromatolites), and from opti-
cally active (birefringent) compounds in radiometrically dated rocks. Living
organisms can produce compounds either in the dextrorotatory form that
rotates polarized light to the right or in the levorotatory form. Inorganic
synthesis produces a 50:50 mixture and solutions of the synthesized com-
pounds are optically neutral. Thus, birefringent compounds can provide
evidence of life in the absence of structurally preserved fossils and in rocks
from other planets and extraterrestrial bodies (so far, negative), and they
provide a means of assessing the organic nature of morphologically unique
microscopic structures found in ancient Precambrian rocks on Earth.
When the Earth's strata were placed in proper sequence following the
principles of stratigraphy and superposition, the geologic record revealed
that the complexity and diversity of life increased in a timeframe also mea-
sured in eons of time. Furthermore, new forms appeared, while others like
trilobites, saber-toothed tigers, giant ground sloths, Irish elks, dinosaurs,
tree-sized lycopods and horsetails, seed ferns, and the cycadlike Bennet-
