Untouched For The Last Billion Years, Water In Canadian Mine Holds Ingredients For Life
Scientists may have discovered the oldest free-flowing source of isolated water ever known.
Scienti…
Geophysicists fingerprint sea-level rise
By considering the unique sea-level “fingerprint” created by a melting ice sheet, a team of geophysicists in North America has developed a new method for pinpointing the sources of global sea-level rise. Their approach could provide a way to measure the impact of the Greenland and West Antarctic ice sheets – the greatest sources of uncertainty in projections of future sea-level changes.
Long-term variations in sea level are caused by processes including thermal expansion of the water, changes in ocean circulation, and changes in the size of glaciers and ice sheets. Measurements from tide gauges indicate a global average sea-level rise of 1–2 mm/yr during the 20th century. However, this estimate ignores geographical variations in sea level, and provides no information about the contribution of different processes.
One possible way to pick apart the total sea-level change is to look for the distinct pattern, or fingerprint, of a melting ice sheet. Close to the ice sheet, for example, the sea level tends to fall. This is a result of both the local uplift of the Earth’s crust after being relieved of the great weight of the ice and a reduction in the ice sheet’s gravitational pull on the ocean. Moving further away from the ice sheet, however, the sea level rises progressively.
“Dinosaur-Killer” Asteroid Impacts Are Much More Common Than We Thought
Think the asteroid that wiped out the dinosaurs was bad? Think again. Two newly published studies on tiny geological features called “spherules” suggest that impact events of this magnitude and greater have actually been commonplace throughout Earth’s early history.
In fact, these brand new findings indicate that massive, “dinosaur-killer” asteroids were likely part of a larger barrage of extraterrestrial impact events that endured for billions of years longer than previously believed. Earth’s history just got a lot more violent.
Both studies, published together in this week’s issue of Nature, are largely concerned with tiny, millimeter-wide droplets known as spherules, which researchers have found embedded in layers of rock all over the world. You can think of spherules as the fingerprints left behind by enormous impact events.
When a massive asteroid rams into Earth, the sheer force of the collision is powerful enough to send plumes of molten and vaporized rock careening out into space. Jettisoned material that fails to escape Earth’s gravitational pull cools, condenses and solidifies into spherules. When they return to Earth, these tiny particles coat the planet’s surface in a thin layer known as a spherule bed. Billions of years later, researchers can examine these layers and estimate when a particular spherule bed formed. The layer of spherules found in the rock sample featured here, for example, dates to about 2.63 billion years ago.
Shifting ocean currents can (and do) actually speed up Earth’s rotation
Time just flies by, and that was especially true during the first half of November 2009, when the Earth’s daily spin around its axis became 0.1 milliseconds shorter. You can blame that lost time on the waters around Antarctica.
Back in November 2009, something strange happened the Southern Ocean. The Antarctic Circumpolar Current suddenly slowed down. The change in current was extreme enough to throw off the planet’s angular momentum, and so to compensate, the Earth sped up its rotation. For about two weeks, the days were a tenth of a millisecond shorter than they should be. Then, with just as little warning, the current returned to its normal speed, and the Earth slowed back down.
Such rotation-altering phenomena aren’t unknown, but they usually take the form of changing wind formations instead of ocean currents. It’s also unprecedented to see such a large change from the oceans throw off the Earth’s rotation so quickly, according to Stephen Marcus and fellow researchers at NASA’s Jet Propulsion Laboratory.
The big question is why this happened - as New Scientist reports, it’s possible that the root of all this may be El Niño. The unusual climate pattern could have thrown off wind speeds around Antarctica, which in turn would have driven the current to slow down. That points to a possible link between climate change, which has made El Niño occur more frequently, and these shifts in Earth’s rotation.
While this sort of temporary, tiny rotation change isn’t that big a deal as these things go, some of the other side effects of alterations to the Antarctic Circumpolar Orbit are more of a concern. The frozen continent’s ice sheets and glaciers are linked to the currents, and an unexpected, sudden change in one could impact the other. And, of course, there’s still the little matter of those lost 1.5 milliseconds worth of productivity back in November 2009. Well, at least I now know why I never finished my novel.
