The debate
over climate change and its effects is often headline news. In the near future,
scientists are concerned that the Earth will experience a continuing increase
in global temperature. New research is showing that even if this increase is
only a few degrees, it could have important repercussions for life on our
planet.
Scientists from the Open University in the United Kingdom are studying climate change throughout Earth's history. Their results indicate how dangerous modern global climate change might be for the future
of life on Earth. In a study published in the March issue of Geology, Christopher Pearce and colleagues examined layers of sedimentary rocks from the ocean floor in order to unravel the story of climate change during the early Jurassic
period.
Oceans losing
oxygen
During the
Jurassic, abrupt global warming of between 9 and 18 Fahrenheit (5 and 10
degrees Celsius) was associated with severe environmental change. Many
organisms went extinct and the global carbon cycle was thrown off balance. One
of the most intriguing effects was that the oxygen content of the oceans
became drastically reduced, and this caused many marine species to die off.
These
intervals of reduced oxygen content in the oceans are now known as oceanic
anoxic events, or OAEs. OAEs are associated with periods of global warming and
have occurred a few times in Earth's history. In the recent study, researchers
focused specifically on the Toarcian OAE, a well-documented OAE from the early
Jurassic.
During
OAEs, the remains of dead organisms and other organic matter accumulate on the ocean
floor and became layers of organic-rich sediments.
Today, scientists are examining the chemical and isotopic compositions of these
sedimentary deposits in order to determine the actual extent to which the
oceans became anoxic. By doing so, they have been able to draw connections
between oxygen-depleted oceans and the disruption of Earth's carbon
cycle.
The carbon
cycle on Earth is one of the most important cycles for life as we know it.
Carbon is a primary building block of life and is present in every living
organism. In order for life to survive on our planet, carbon must cycle between
the atmosphere, geosphere (land), hydrosphere (water) and biosphere (life). If
the carbon cycle were to suddenly become disrupted, many forms of life on Earth
would not survive. Even minor disruptions in the carbon cycle can have profound
consequences for living organisms.
By studying
organic-rich marine deposits from the Toarcian OAE, the Open University
researchers were able to compare the oxygen levels of ancient seawater to the
oceans of today. The sedimentary rocks contain molybdenum, whose isotopic
composition is altered depending on how oxygenated the seawater was when the
sediments formed. By studying how the isotopic composition of molybdenum
changed during the Toarcian OAE, scientists have developed a unique way to
trace fluctuations in the oxygen content of Earth's oceans.
The Open
University team determined that major disruptions in the global carbon cycle
during the Jurassic period were intimately linked with the development of
anoxic oceans and with global warming. Ultimately, this ties global warming to
the demise
of numerous life forms on Earth millions of years ago. Additionally, the
research is providing insight into how the Earth's oceans and atmosphere evolved
over time.
Our climate
in the balance
Modern
studies of global climate change on Earth usually rely on computer modeling
techniques. However, studying the history of our planet through geology can
provide information on actual occurrences of climate change in the past.
Dr. Anthony
Cohen, a member of the research team, commented: "The use of current computer
models to try to predict the course of climate and environmental conditions in the
longer term is uncertain because of our relatively poor understanding of the
great complexity of the Earth's behaviour. In contrast, marine sedimentary
records can provide quantifiable information about precisely how the Earth has
responded to severe environmental change in the past. Therefore, these records
may also provide valuable constraints for testing the reliability of
predictions about environmental change that will continue to occur in the
future as a result of man's activities."
Although
the Toarcian OAE occurred roughly 183 million years ago, the findings of the
recent study have important implications for our understanding of climate
change today. The rates and magnitude of environmental change during ancient
OAEs appear to have been similar to what we see occurring in modern times.
By studying
OAEs, scientists are able to gain important clues about how climate change
might impact life on Earth in the in the coming centuries. Hopefully, their
work will lead to scientific solutions that could prevent the same devastating
affects on the Earth's carbon cycle — and life itself — that were caused by
global warming during the Jurassic period.
advertisement
