Earth & Environment

Earth’s bulging waistline, plus ancient mangrove swamps and new threats from wildfires in this week’s news

Ice melt boosts planet’s waistline Melting ice has changed the shape of Earth, making it more bulgy at the equator. Scientists understand most of the things that affect the planet’s shape, such as tides and weather, but satellite measurements between 1975 and 2009 show an unexplained change starting in the mid-1990s. Researchers at the University of Colorado at Boulder have now combined those measurements with data from the gravity-sensing GRACE satellites, and report that ice melting off Greenland and Antarctica is to blame. Solid ice near the poles has transformed into liquid water distributed around the planet, the team reports in an upcoming Geophysical Research Letters . — Alexandra Witze

Ancient mangroves absorb modern earthquakes
Buried remnants of mangrove swamps help to soak up the shock of earthquakes, protecting island coasts from damage. A new analysis of sites in the French Antilles suggests that these soft deposits protect the stiffer overlying soil from deforming. The effect is similar to that provided by dampening systems made of rubber that have been developed for buildings in earthquake-prone areas, French researchers report in the June issue of the Bulletin of the Seismological Society of America. —Devin Powell

Fires amplify soils’ climate, ozone threat
Wildfires can dramatically boost grasslands’ release of nitrous oxide, a greenhouse gas and threat to atmospheric ozone, field data indicate. In 2003, a wildfire swept through an area of California grassland set aside to study factors affecting the release of greenhouse gases from soil. Nitrous oxide values didn’t change much within the first year after the fire. But for at least two years after that, emissions increased by as much as sixfold, an international group reports June 8 in PLoS ONE. The researchers suspect the fire allowed bacteria, which had been previously limited by too much oxygen and too little carbon and nitrogen, to readily convert soil nutrients into nitrous oxide. —Janet Raloff

Earth’s early core
Something happened deep inside the Earth a couple of billion years ago. New studies of ancient rocks reveal how strong the Earth’s magnetic field was at various points in the past as its liquid core began to cool and solidify. Some 2 billion years ago, perhaps as the solid inner core went through a growth spurt, the difference between the north and south magnetic poles became surprisingly weaker, scientists led by Aleksey Smirnov, of Michigan Technological University in Houghton, report in an upcoming Physics of the Earth and Planetary Interiors. —Alexandra Witze

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