Horn corals about 450 million years old; they’re often found in the fossil record. Credit: Shanan Peters |
Much
of our knowledge about past life has come from the fossil record, but
how accurately does that record reflect the true history and drivers of
biodiversity on Earth?
“It’s
a question that goes back a long way to the time of Darwin, who looked
at the fossil record and tried to understand what it tells us about the
history of life,” says Shanan Peters, a geoscientist at the University
of Wisconsin-Madison.
In fact, the fossil record can tell us a great deal, Peters says in results of a new study.
In a paper published this week in the journal Science,
he and colleague Bjarte Hannisdal of the University of Bergen in Norway
show that the evolution of marine life over the past 500 million years
has been driven by both ocean chemistry and sea-level changes.
“These
results tell us that the number of species in the oceans through time
has been influenced by the amount and availability of carbon, oxygen and
sulfur, and by sea level,” says Lisa Boush, program director in the
National Science Foundation (NSF)’s Division of Earth Sciences, which
funded the research.
“The
study allows us to better understand how modern changes in the
environment might affect biodiversity today–and in the future.”
The
time period studied covers most of the Phanerozoic eon, which extends
to the present and includes the evolution of most plant and animal life.
Hannisdal and Peters analyzed fossil data from the Paleobiology Database, along with paleoenvironmental proxy records and data on the rock record.
These
data reflect ancient global climates, tectonic movements, continental
flooding and changes in biogeochemistry, especially in Earth’s oxygen,
carbon and sulfur cycles.
The
scientists used a method called information transfer, which allowed
them to identify causal relationships, not just general associations,
between biodiversity and environmental proxy records.
“We
find an interesting web of connections between these different systems,
which combine to drive what we see in the fossil record,” Peters says.
For
example, marine biodiversity is closely related to the sulfur cycle,
says Peters. The “signal” from sea-level–how much the continents are
covered by shallow seas–is also important in the history of marine
animal diversity, the researchers found.
The
dramatic changes in marine biodiversity seen in the fossil record,
Peters says, “likely arose through biological responses to changes in
the global carbon and sulfur cycles, and to sea level, through geologic
time.”
Despite
its incompleteness, the fossil record is a good representation of
marine biodiversity over the past half-billion years, the scientists
believe.
The findings also emphasize the interconnectedness of Earth’s physical, chemical and biological processes.
“Earth
systems are all connected,” says Peters. “It’s important to realize
that when we perturb one thing, we’re not just affecting that one thing.
“The
challenge is understanding how that perturbation of one thing, for
example, the carbon cycle, will affect the future biodiversity of the
planet.”
