Related : The history of the world is written in tree rings. Scientists call this particular magnetic reversal the Laschamps excursion. They can date this event by studying the rock record. The Laschamps excursion lasted only a few hundred years, but scientists are interested in it because they think it might help them figure out how a magnetic reversal might have affected creatures living on Earth at the time. But being able to link them to this event is the real trick.
Some of these ancient coniferous trees are still living in New Zealand today and their antecedents have been around since the Jurassic period, millions of years ago, Gramling says. The particular trees in this peat bog date to about 50, years ago. Similarly, reversal patterns do not match patterns in species extinction during geological history.
Some animals, such as pigeons and whales, may use the Earth's magnetic field for direction finding. Assuming that a reversal takes a number of thousand years, that is, over many generations of each species, each animal may well adapt to the changing magnetic environment, or develop different methods of navigation. The source of the magnetic field is the iron-rich liquid outer core of the Earth.
This liquid moves in complex ways as a result of the convection of the heat deep within the core and of the rotation of the planet. The motion of the core fluid is continuous and never stops, even during a reversal. It can only stop when the energy source fails. Heat is produced at least partly because of the solidification of the liquid core onto the solid inner core that sits at the centre of the Earth. This process has operated continuously over billions of years.
At the top of the liquid core, some km beneath our feet and below the rocky mantle, the fluid may travel at horizontal speeds of tens of kilometres per year. The motion of this metal fluid across existing magnetic field lines of force produces electrical currents and these, in turn, generate more magnetic field. This is a process known as advection. To balance any growth of the field, and thus stabilise what we call the 'geodynamo', we need diffusion, where field 'leaks' away from the core and is destroyed.
Ultimately, the core fluid flow produces a complicated magnetic field pattern at the Earth's surface with a complicated time variation. Simulations of the geodynamo on supercomputers have demonstrated the complex nature of the field and its behaviour over time. Simulations have also revealed reversals in the polarity, where the magnetic North pole is replaced by a South pole, and vice versa. The solid iron inner core of the Earth has been shown in these simulations to be important in controlling the reversal process.
Because it is a solid, the inner core can't generate magnetic field by advection, but any field that is generated in the fluid outer core can diffuse, or spread, into the inner core. The field generation process advection in the outer core seems to regularly attempt to reverse. But unless the field locked into the inner core first diffuses away, a true reversed field cannot become established throughout the core.
Essentially the inner core resists any 'new' field diffusing in and perhaps only one in every ten such reversal attempts is successful. It is worth stressing that these results, while fascinating in themselves, are not known to be strictly true of the 'real' Earth. However, we have mathematical models of the Earth's magnetic field for the last years, with early models based largely on observations made by mariners engaged in merchant and naval shipping.
From these models and extrapolating down into the Earth, it is known that regions of reversed flux at the core-mantle boundary have grown over time.
In a marked reversal from past elections, a majority of Asian-Americans went Republican, as did a third of Latino voters. In the future, the ship could be fitted with futuristic lasers and electro-magnetic rail-guns too. New sanctions now would lead to the collapse of the talks and a reversal of progress already made. Both are the result of magnetic activity on the sun, but a solar flare has more energy than a CME. He went off whistling, and Isabel raised her hand and looked at it meditatively; his own had been unexpectedly warm and magnetic.
This decision meant a complete reversal of Swedish foreign policy and a breach with France. She came with an easy smile into the little group, and immediately her magnetic presence seemed to rivet all attention. Thus, the magnetic telegraph was expected for quite three hundred years before its first tap of the keys announced its presence.
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