Methane and mini-horses: Fossils reveal effects of global warming
DENVER, Colo.How will global warming affect
life on Earth? Uncertainties about future climate change and the
impact of human activity make it difficult to predict exactly what
lies ahead. But the past offers clues, say scientists who are studying
a period of warming that occurred about 55 million years ago.
In a joint project of the University of Michigan,
the University of New Hampshire and the Smithsonian Institution,
researchers have been analyzing fossils from the badlands of Wyoming
found in a distinctive layer of bright red sedimentary rock that
was deposited at the boundary between the Paleocene and Eocene epochsa
time of apparent sudden climate change. The researchers described
their findings in a paper presented Feb. 16 at the annual meeting
of the American Association for the Advancement of Science.
"The interval of Earth history that we're
studying is marked by a short-term global warming event thought
to have occurred when something triggered the release of methane
from methane clathratea kind of 'methane ice'
found in ocean sediments," said Philip D. Gingerich, professor
of geological sciences at the University of Michigan. Within about
10,000 years of peak warming, mammals such as primates and the groups
that include horses and deer appeared together for the first time
in North America, apparently having crossed land bridges from other
As the warm spell continued, the animals showed
an intriguing response: they became smaller. For example, "horses
from this period that had been the size of a small dog were reduced
to the size of a Siamese cat," Gingerich said. When the climate
returned to normal, the animals became normal size again. To understand
why dwarf versions of the various animals appeared and then disappeared
from the fossil record, Gingerich turned to colleagues at the University
of Michigan Biological Station who are studying the effects of elevated
carbon dioxide levelsassociated with global warmingon
"They find that if you grow plants in a
carbon dioxide-rich atmosphere, the plants love it. They grow fast.
It's easy for them." But in the process, the plants
incorporate less protein and more defensive compounds than they
normally would. Insects that eat these plants grow more slowly,
and the same might be true of mammals, Gingerich reasoned.
Furthermore, "the reproductive cycles of
mammals that live in seasonal environments are tuned to seasonal
cycles," Gingerich said. "If an animal has a one- or
two-year period in which to grow to maturity and reproduce, and
it's trying to do that on a diet that's difficult to
digest and not very nutritious, it's not surprising that it
would evolve to be smaller. And it's also not surprising that
when times are good again and carbon dioxide levels are lower and
plants grow like they normally should, that the animals would go
back to what we think of as their normal size."
It's not clear whether the body size trends
represent true evolutionary change or whether the larger species
were simply replaced by smaller sister species, but Gingerich hopes
to answer that question as he continues to work on the project.
He and his coworkers, William C. Clyde of the
University of New Hampshire and Scott L. Wing and Guy J. Harrington
of the Smithsonian Institution, also hope their work will improve
understanding of climate change in general.
"This is a model of an event in the past
that involved change and recovery from change," Gingerich
said. "During that 80,000-year period, mammals didn't
go extinct; they adapted through dwarfing. And eventually, the system
worked itself back to the previous state."
But just because Earth and its inhabitants recovered
from global warming in the past don't assume we have nothing
to worry about now, Gingerich cautions. "In today's
Earth, additional warming could set off a methane release that would
bump the Earth's temperature up by several degreesenough
to melt polar ice and raise sea level and cause many other problems
that would be difficult to survive. That's what makes the
temperature rises we're measuring now more worrisome than
those that occurred in the past."
Contact: Nancy Ross-Flanigan
Phone: (734) 647-1853