The Paleocene–Eocene Thermal Maximum lasted around 20,000 years, and was superimposed on the Eocene -a 6-million-year period of more gradual global warming,
During the Eocene around 1,500 to 2,000 gigatons of carbon were released into the ocean/atmosphere system over the course of 1,000 years. This rate of carbon addition -which peaked during the PETM- almost equals the rate at which carbon is being released into the atmosphere today through human activity.
The team of scientists from Caltech and McGill University, discovered microscopic, magnetic fossils resembling spears and spindles, unlike anything previously seen, among sediment layers deposited during an ancient global-warming event along the Atlantic coastal plain of the United States.
"Imagine our surprise to discover not only a fossil bloom of bacteria
that make iron-oxide magnets within their cells, but also an entirely
unknown set of organisms that grew magnetic crystals to giant sizes,"
said Caltech"s Timothy Raub, who collected the
samples from an International Ocean Drilling Program drill-core
storehouse at Rutgers University in New Jersey. The research team believes these
fossils may be telling a story of radical environmental transformation
Perhaps in response to the environmental stress of the PETM, many land
mammals in North America became dwarfed. Almost half of the common sea
bottom-dwelling microorganisms known as foraminifera became extinct in
newly warmer waters that were incapable of carrying the levels of
dissolved oxygen for which they were adapted.
A typical "giant" spearhead-shaped crystal is only about four microns
long, which means that hundreds would fit on the period at the end of
this sentence. However, the crystals found recently are eight times
larger than the previous world record for the largest bacterial
iron-oxide crystal.
According to Dirk Schumann, a geologist and electron microscopist at
McGill University and lead author of the study, "It was easy to focus
on the thousands of other bacterial fossils, but these single, unusual
crystals kept appearing in the background. It soon became evident that
they were everywhere."
In addition to their unusually large sizes, the magnetic crystals occur
in a surprising array of shapes. For example, the spearhead-like
crystals have a six-sided "stalk" at one end, a bulbous middle, and a
sharp, tapered tip at the other end. Once reaching a certain size,
spearhead crystals grow longer but not wider, a directed growth pattern
that is characteristic of most higher biological organisms.
The spearhead magnetic crystals compose a minor fraction of all of the
iron-oxide crystals in the PETM clay layer. Most of the crystals have
smaller sizes and special shapes, which indicate that they are fossils
of magnetotactic bacteria. This group of microorganisms, long studied
at Caltech by study coauthor Joseph Kirschvink, the Nico and Marilyn
Van Wingen Professor of Geobiology, use magnets to orient themselves
within Earth"s magnetic field, and proliferate in oxygen-poor water.
Spearheads are not, however, the rarest fossil type in the deposit.
That honor belongs to a spherical cluster of spearheads informally
dubbed the "Magnetic Death Star" by the researchers. The Magnetic Death
Star may have preserved the crystals as they occurred in their original
biological structure.
The researchers could not find a similar-shaped organism anywhere in
the paleontological annals. They hypothesize that it may have been a
single-celled eukaryote that evolved for the first time during the PETM
and was outcompeted once the strange climate conditions of that time
diminished. Alternatively, it may still exist today in a currently
undiscovered location.
"The continental shelf of the mid-Atlantic states during the PETM must
have been very iron-rich, much like the Amazon shelf today," notes
study coauthor Robert Kopp of Princeton University, who first started
working on the project while a graduate student at Caltech. "These
fossils may be telling a story of radical environmental transformation:
imagine a river like the Amazon flowing at least occasionally where the
Potomac is today."
The Caltech work was supported by the NASA Exobiology program.
Posted by Casey Kazan from materials provided by California Institute of Technology.
Source: : http://mr.caltech.edu/press_releases/13195