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Book Reviews:
Life on a Young Planet
Maps:
New Nevada elements maps from the U.S. Geological Survey
Book
Reviews
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Life on a Young Planet:
The First Three Billion Years of Evolution on Earth
by Andrew H. Knoll. Princeton
University Press, 2003. ISBN 0 6910 0978 3. Hardcover, $29.95.
Alan Jay Kaufman
|
If literature is the distillation of the human experience, Life on a Young
Planet is the distillation of Andrew Knoll’s exuberant 25-year scientific
experience across the four corners of the Precambrian world. Through the sharp
view of his hand lens, microscope and mass spectrometer, Knoll documents a 3-billion-year
window of environmental and biological evolution leading to the Cambrian explosion
of animal life. Through this enterprise, he comments on many of the great discoveries
of the Precambrian world, as well as those to come in both time and space.
Life on a Young Planet is a remarkably literary, integrative and generous
book. Although Knoll makes eloquent arguments that support his personal bias,
he also makes a point to present opposing sides of the scientific debate. He tells
his history (and that of the rocks) with the assistance of colorful colleagues,
who collectively study the ancient world, in part, Knoll argues, to prepare us
for astrobiological discoveries in our future.
Knoll begins in fossiliferous strata that represent a recognized flaw in Darwin’s
theory of evolution — no visible animal ancestors were known from underlying
rocks. There, he casts his gaze from colleagues standing on Cambrian beds in Siberia
(Chapter 1) back to the base of the tree of life. Next, he climbs the branches
to the origin of animals — and Darwin’s dilemma — by taking a walkabout
across Precambrian cratons and along the way documenting “the co-evolution
of Earth and life.” By framing the book around his own field studies, Knoll
provides markers along the Precambrian continuum, where he explores critical events
in Earth’s history. These virtual field trips are bridged with scholarly
(yet digestible at upper undergraduate and higher levels) discussions about the
origin of life and biological evolution, biochemistry and molecular phylogeny,
paleontology, geology and geochemistry.
In this paleontologic odyssey (see timeline, in print copy of magazine), Knoll
travels to the frozen landscape of Spitzbergen (Chapter 3) — where he began
his post-graduate academic journey — to learn about life’s clear imprint
on rocks deposited some 700 to 800 million years ago, just before Cambrian animals
arrived on the scene. In stark contrast, the origin of organic remains preserved
in 3.5-billion-year-old sediments from western Australia (Chapter 4) are much
less clear. Through the thick red dust of the outback (an apropos setting for
future astrobiological studies on Mars), Knoll wipes off his glasses to focus
on the highly debated paleontologic evidence on Earth for the earliest prokaryotic
life and stromatolites (columnar or dome-shaped structures formed by layered microbial
mats that trap, bind or precipitate sediments).
From here, he pays homage to the 1.85-billion-year-old banded-iron formations
of southern Canada (Chapter 6) to explore the photosynthetic revolution of cyanobacteria
that resulted in the oxygenation of Earth’s surface environments. Based on
studies of these same sediments, Knoll’s “academic father,” Elso
Barghoorn, established the field of Precambrian paleobiology more than half a
century ago.
Knoll then journeys to the 1.4-billion-year-old fossiliferous strata in arctic
Siberia, documenting the ascent of the cyanobacteria as modifiers of Earth’s
surface environment during the middle age of the Precambrian. His Precambrian
world tour then ascends the geological column back to events that represent the
“smoldering fuse” of the coming Cambrian explosion, including 600-million-year-old
sediments from South China (Chapter 9) that contain the first signs of embryonic
animal life. Venturing next to slightly younger strata in southern Namibia (Chapter
10), Knoll discusses an evolutionary dead end for Earth’s earliest presumptive
animals: the oddball Ediacaran metazoans that rapidly diversified just a few million
years before the Precambrian-Cambrian boundary and then just as suddenly disappeared
in an environmental catastrophe of global proportions.
While most of the Ediacaran animals appear to have succumbed to the first great
mass extinction, other animals better able to confront the ecological crisis must
have survived to populate Cambrian seas. Indeed, according to Knoll, the tumultuous
tectonic, climatic and environmental perturbations of the last 200 million years
of the Precambrian — including a series of potentially long-lived global
ice ages, remarkable oscillations in the carbon cycle and the dramatic rise of
atmospheric oxygen — strongly impacted subsequent animal evolution. This
view, which Darwin could not appreciate, ties “genetic possibilities with
ecological opportunities.” Moreover, Knoll writes, “Earth’s long
Precambrian history provides illuminating perspective on the great idea of twenty-first-century
Earth science — that biology is inexorably linked with tectonics and climate,
atmosphere and oceans in a complex and interactive Earth surface system.”
Having climbed through the tree of life back to modern animal branches, Knoll
leaps to a different tree, rooted in otherworldly soils; he returns to humanity’s
oldest question, “Are we alone in the universe?” True to the primary
thesis of Life on a Young Planet, Knoll — a lead investigator in NASA’s
Astrobiology Institute — suggests that it is more likely we will recognize
life beyond our planet by its environmental impact, rather than by debate on simple
structures in a small meteorite from Mars.
Life on a Young Planet is as much about the history of science as it is
scientific history. Knoll paints his integrative research against the historical
canvas of 20th-century discoveries and controversies. Picking up the torch that
longtime Harvard colleague Stephen J. Gould left in his passing, Knoll concludes
that there can be no scientific resolution to creationists’ parables.
Kaufman is an associate professor
of geochemistry in the University of Maryland’s Department of Geology.
His Precambrian research focuses on charting the course of chemical changes
in Earth’s surface environments and the relationship of these changes to
biological evolution.
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Maps
New
Nevada elements maps
Two geochemical surveys covering the Humboldt River Basin in Nevada took place
from 1990 through 2000 in conjunction with the Bureau of Land Management (BLM),
for the purpose of assessing the mineral resource potential and environmental
health of federal lands under the stewardship of the Department of the Interior.
The combined surveys consist of geochemical analyses of stream-sediment and
soil samples for approximately 40 elements. Of these elements, the U.S. Geological
Survey (USGS) and BLM identified thirteen elements (scandium, iron, cobalt,
copper, nickel, zinc, arsenic, selenium, silver, antimony, cesium, gold and
lead) for their importance in identifying mineral deposits or as potential toxins
in the environment.
A 1:500,000-scale map was published for each element, in which geochemical point
data are represented as calculated abundances above and below the mean. Thus,
each map provides a useful tool in interpreting trends and anomalies in element
concentration throughout the Humboldt River Basin and vicinity.
Geochemical data used for this study mainly came from over 7,000 stream-sediment
and soil samples that were originally collected during the National Uranium
Resource Evaluation (NURE) program of the 1970s. The data were recently reanalyzed
as part of the 1994 Winnemucca-Surprise mineral resource assessment and the
1996 USGS Humboldt River Basin mineral and environmental assessment. Sample
coverage for the combined datasets is generally spatially uniform, with a sample
density of one sample site per 17 square kilometers, with the highest sample
density present along range fronts and the sparsest density along mountain ridges
and valley bottoms.
MF-2407-A-M.
NEVADA. Maps showing concentrations of 13 elements from stream sediments
and soils throughout the Humboldt River Basin and surrounding areas, northern
Nevada, by D.B. Yager and H.W. Folger. 2003. Scale 1:500,000. All sheets
color, 44 X 42 inches. Available for $20.00 per sheet from USGS Information
Services or free online.
MF-2407-A.
Map showing scandium concentrations from stream sediments and soils throughout
the Humboldt River Basin and surrounding areas.
MF-2407-B.
Map showing iron concentrations from stream sediments and soils throughout the
Humboldt River Basin and surrounding areas.
MF-2407-C.
Map showing cobalt concentrations from stream sediments and soils throughout
the Humboldt River Basin and surrounding areas.
MF-2407-D.
Map showing nickel concentrations from stream sediments and soils
throughout the Humboldt River Basin and surrounding areas.
MF-2407-E.
Map showing copper concentrations from stream sediments and soils
throughout the Humboldt River Basin and surrounding areas.
MF-2407-F.
Map showing zinc concentrations from stream sediments and soils
throughout the Humboldt River Basin and surrounding areas.
MF-2407-G.
Map showing arsenic concentrations from stream sediments and soils
throughout the Humboldt River Basin and surrounding areas.
MF-2407-H.
Map showing selenium concentrations from stream sediments and soils
throughout the Humboldt River Basin and surrounding areas.
MF-2407-I.
Map showing silver concentrations from stream sediments and soils
throughout the Humboldt River Basin and surrounding areas.
MF-2407-J.
Map showing antimony concentrations from stream sediments and soils
throughout the Humboldt River Basin and surrounding areas.
MF-2407-K.
MF Map showing cesium concentrations from stream sediments and soils
throughout the Humboldt River Basin and surrounding areas.
MF-2407-L.
Map showing gold concentrations from stream sediments and soils
throughout the Humboldt River Basin and surrounding areas.
MF-2407-M.
Map showing lead concentrations from stream sediments and soils throughout the
Humboldt River Basin and surrounding areas.
To order USGS maps: Contact USGS Information Services, P.O. Box 25286,
Denver, Colo. 80225. Phone: 888-ASK-USGS (888/275-8747).
Randall Orndorff compiles
the Maps section and is the Associate Program Coordinator for the USGS National
Cooperative Geologic Mapping Program. Email: rorndorf@usgs.gov.
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