Sources and Sinks

Re-Blogged From EurekAlert

For the entire history of our species, humans have lived on a planet capped by a chunk of ice at each pole. But Earth has been ice-free for about 75 percent of the time since complex life first appeared. This variation in background climate, between partly glaciated and ice-free, has puzzled geologists for decades.

Now a team of scientists led by UC Santa Barbara’s Francis Macdonald has published a study suggesting that tectonic activity may be the culprit. They found that long-term trends in Earth’s climate are set by the presence or absence of collisions between volcanic arcs and continents in the tropics. The results appear in the journal Science.

“There’ve been a few hypotheses but no agreements as to why we have warmer or colder climates on these very long timescales,” said Macdonald, a professor in the Department of Earth Science.

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Old Stone Walls Record History of Earth’s Magnetic Wanderings

By Liza Lester – Re-Blogged From AGU 100

Under the forests of New York and New England, a hidden tracery of tumbledown stone walls marks the boundaries of early American farms, long abandoned for city jobs and less stony pastures in the West.

These monuments of an agrarian past also mark past locations of Earth’s itinerant magnetic north pole, a record leveraged by geochemist and local history buff John Delano to reconstruct a history of our planet’s magnetic field in eastern North America in a new study published in AGU’s Journal of Geophysical Research: Solid Earth.

An old stone wall marks a boundary of a long-abandoned farm near Grafton, New York, once part of the colonial Manor of Rensselaerwyck. A section of the 700,000-acre manor west of the Hudson River was was surveyed for rental allotments in 1787. Credit: John Delano

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