For example, it's thought that CAMP emitted a total of more than 2 million cubic kilometers of lava. If that amount of lava were spewed over a period of 1 million to 2 million years, it wouldn't have nearly the impact it would if it were emitted over tens of thousands of years. "The timescale over which the eruption occurred has a big effect," Bowring says.
Tilting toward extinction
To determine how long the volcanic eruptions lasted, the group combined two dating techniques: astrochronology and geochronology. The former is a technique that links sedimentary layers in rocks to changes in the tilt of the Earth: For decades, scientists have observed that the Earth's orientation changes in regular cycles as a result of gravitational forces exerted by neighboring planets. For example, the Earth's axis tilts at regular cycles, returning to its original tilt every 26,000 years. Such orbital variations change the amount of solar radiation reaching the Earth's surface, which in turn has an effect on the planet's climate, known as Milankovich cycles. The result of the climatic change can be preserved in the cyclicity of sediments deposited in the Earth's crust.
Scientists can determine a rock's age by first identifying cyclical variations in deposition of sediments in quiet bodies of water, such as deep oceans or large lakes. A cycle of sediment corresponds with a cycle of the Earth's tilt, established as a known period of years. By seeing where a rock lies in those sedimentary layers, scientists can get a good idea of how old it is. To get precise estimates, scientists have developed mathematical models to determine the Earth's tilt over millions of years.
Bowring says the technique is good for directly dating rocks up to 35 million years old, but beyond that, it's unclear how reliable the technique can be. His team used astrochronology to estimate the age of the sedim
|Contact: Sarah McDonnell|
Massachusetts Institute of Technology