Scientists probe link between magnetic polarity reversal and heat in planet’s interior

August 3, 2012 – EARTH - Scientists at the University of Liverpool have discovered that variations in the long-term reversal rate of the Earth’s magnetic field may be caused by changes in heat flow from the Earth’s core into the base of the overlying mantle. The Earth is made up of a solid inner core, surrounded by a liquid outer core, in turn covered by a thicker or more viscous mantle, and ultimately by the solid crust beneath our feet. The magnetic field is generated by the motions of the liquid iron alloy in the outer core, approximately 3,000 km beneath the Earth’s crust. These motions occur because the core is losing heat to the overlying solid mantle that extends up to the crust on which we live. The mantle itself is also in motion but at much slower speeds of millimetres per year as opposed to millimetres per second in the core. This mantle motion is responsible for the drifting of the continents at the surface as well as earthquakes, volcanoes, and changes in the climate over millions of years. At intervals of hundreds of thousands of years, the North and South magnetic poles reverse and scientists can tell from rock formations precisely at what periods in the past this took place. The most recent reversal happened 780,000 years ago. Magnetic field variations happen on timescales of months to millions of years. Much of the magnetic field’s variation is thought to be sporadic but new research, led by Liverpool scientists, has found that over long timescales, this variability may be related to the changing pattern of heat loss across the core-mantle boundary occurring over millions of years. The team performed a detailed synthesis based on latest findings from a number of different areas including the ancient geomagnetic field and its record in rocks, motions in the mantle caused by motions of the continents and the process responsible for generating the magnetic field in the core. Dr Andrew Biggin, from the University’s School of Environmental Sciences, said: “The magnetic field has undergone big changes in its behavior that might be due to the mantle’s controlling influence on the core. In particular, we focused on the time interval between around 200 and 80 million years ago – when dinosaurs were still around – when the magnetic field initially started reversing its polarity very frequently. During this period the polarity was reversing up to 10 times every million years; however 50 million years later, it stopped reversing altogether for nearly 40 million years. “When these changes in the magnetic field were taking place, the whole of the Earth’s crust and mantle, including all of the continents, were undergoing a big rotation with respect to the geographic and time-averaged geomagnetic poles – the points defining the Earth’s axis of rotation. We suspect that this process, called True Polar Wander and caused by the changing density distribution in the mantle, will have changed the pattern of heat flowing out of the core in such a manner as to cause the magnetic field to first become less stable, with lots of reversals, and then become much more stable – and stop reversing.” –Terra Earth

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Why did Earth thrive and our sister planet, Venus, died? From the fires of a sun's birth... twin planets emerged. Then their paths diverged. Nature draped one world in the greens and blues of life. While enveloping the other in acid clouds... high heat... and volcanic flows. Why did Venus take such a disastrous turn?

For as long as we have gazed upon the stars, they have offered few signs... that somewhere out there... are worlds as rich and diverse as our own. Recently, though, astronomers have found ways to see into the bright lights of nearby stars.

They've been discovering planets at a rapid clip... using observatories like NASA's Kepler space telescope... A French observatory known as Corot ... .And an array of ground-based instruments. The count is approaching 500... and rising. These alien worlds run the gamut... from great gas giants many times the size of our Jupiter... to rocky, charred remnants that burned when their parent star exploded.

Some have wild elliptical orbits... swinging far out into space... then diving into scorching stellar winds. Still others orbit so close to their parent stars that their surfaces are likely bathed in molten rock. Amid these hostile realms, a few bear tantalizing hints of water or ice... ingredients needed to nurture life as we know it. The race to find other Earths has raised anew the ancient question... whether, out in the folds of our galaxy, planets like our own are abundant... and life commonplace? Or whether Earth is a rare Garden of Eden in a barren universe?

With so little direct evidence of these other worlds to go on, we have only the stories of planets within our own solar system to gauge the chances of finding another Earth. Consider, for example, a world that has long had the look and feel of a life-bearing planet. Except for the moon, there's no brighter light in our night skies than the planet Venus... known as both the morning and the evening star.

The ancient Romans named it for their goddess of beauty and love. In time, the master painters transformed this classical symbol into an erotic figure. It was a scientist, Galileo Galilei, who demystified planet Venus... charting its phases as it moved around the sun, drawing it into the ranks of the other planets.

With a similar size and weight, Venus became known as Earth's sister planet. But how Earth-like is it? The Russian scientist Mikkhail Lomonosov caught a tantalizing hint in 1761. As Venus passed in front of the Sun, he witnessed a hair thin luminescence on its edge.

Venus, he found, has an atmosphere. Later observations revealed a thick layer of clouds. Astronomers imagined they were made of water vapor, like those on Earth. Did they obscure stormy, wet conditions below? And did anyone, or anything, live there?

NASA sent Mariner 2 to Venus in 1962... in the first-ever close planetary encounter. Its instruments showed that Venus is nothing at all like Earth. Rather, it's extremely hot, with an atmosphere made up mostly of carbon dioxide.

The data showed that Venus rotates very slowly... only once every 243 Earth days... and it goes in the opposite direction. American and Soviet scientists found out just how strange Venus is when they sent a series of landers down to take direct readings.

Surface temperatures are almost 900 degrees Fahrenheit, hot enough to melt lead, with the air pressure 90 times higher than at sea level on Earth. The air is so thick that it's not a gas, but a "supercritical fluid." Liquid CO2. On our planet, the only naturally occurring source is in the high-temperature, high-pressure environments of undersea volcanoes. It comes in handy for extracting caffeine from coffee beans... or drycleaning our clothes.

You just wouldn't want to have to breathe it. The Soviet Venera landers sent back pictures showing that Venus is a vast garden of rock, with no water in sight. In fact, if you were to smooth out the surface of Venus, all the water in the atmosphere would be just 3 centimeters deep. Compare that to Earth... where the oceans would form a layer 3 kilometers deep.

If you could land on Venus, you'd be treated to tranquil vistas and sunset skies, painted in orange hues. The winds are light, only a few miles per hour... but the air is so thick that a breeze would knock you over. Look up and you'd see fast-moving clouds... streaking around the planet at 300 kilometers per hour. These clouds form a dense high-altitude layer, from 45 to 66 kilometers above the surface.

The clouds are so dense and reflective that Venus absorbs much less solar energy than Earth, even though it's 30% closer to the Sun.