Geology Reference
In-Depth Information
two science teams is remarkably good. Nevertheless, we can anticipate many debates, as
postulated craton locations are shuffled and tweaked for decades to come.
In any case, the assembly of Columbia, commencing 1.9 billion years ago, set the stage
for the boring billion. Whatever the configurational details of the Columbian supercontin-
ent actually were, we can be fairly confident that much of its interior was hot, desiccated
terrain, with absolutely no vegetation and great expanses of rusty desert. Seen from space,
Earth would have appeared as a strangely lopsided world, with its one great enreddened
landmass surrounded by an even more expansive (and as yet unnamed) blue superocean.
With all the continents concentrated together near the Equator, only modest amounts of ice
would have decorated the poles. Ocean levels would have been correspondingly high, per-
haps high enough to invade some coastal regions with shallow inland seas.
The equatorial Columbian supercontinent is the supposed starting point for the dullest
time in Earth history, but what makes it so dull? What does
stasis
really mean—what para-
meters were stable? Was it global climate and rainfall? Was it the nature and distribution
oflife?Wasitthecompositionoftheoceanoratmosphere?Whatmeasurements havebeen
made to establish this alleged stasis? Conversely, what uncertainties remain unaddressed?
Stasis
Most geology graduate students simply ignore rock formations born between 1.85 billion
and 850 million years ago. Four years, while working toward a Ph.D., trying to make a
splashandlandatenure-trackjob,istooshortatimetospendonageologicalerawithsuch
a questionable rap. But Linda Kah was not like most graduate students. Her undergraduate
mentor at MIT was John Grotzinger, a leader in the study of Earth's oldest rocks from be-
fore 2 billion years ago. Her Ph.D. adviser at Harvard was Andy Knoll—the renowned pa-
leontologistwhoencouragedNoraNoffkeinhermicrobialmatresearch.Kahcouldn'thelp
but notice that Earth older than 1.8 billion years (described by Grotzinger) was strikingly
different from Earth younger than 0.8 billion years (described by Knoll). Something inter-
esting must have happened during the boring billion, and Kah was determined to find out
what. And so she has devoted herself to understanding the Mesoproterozoic Era—the im-
mense span of Earth history from 1.6 to 1.0 billion years ago—a time encompassing most
of the boring billion.
Even if the Mesoproterozoic was in fact a time of stasis, a billion years of equilibrium
would be remarkable. Change is the central theme of Earth's story. The oceans and atmo-
sphere,thesurfaceanddeepinterior,thegeosphereandbiosphere—all aspects ofourplan-
et have changed incessantly over the aeons. How could Earth have experienced a billion
years without anydramatic events, with nosignificant transitions inthe near-surface envir-
onments, with no great novelty in the living or nonliving world? Was there really a billion-
