the earth core
the earth core consists of core and outer core, and kernel is a solid iron nickel alloy, the thickness is about 1200 km.and outside nucleus is the core of liquid iron nickel, thickness is about 2200 km.geologists for a long time, think that the earth's core formed about 1 billion years ago.due to temperature drop, at the center of the earth's molten liquid metal began spontaneously rapid crystal growth, has been achieved now is about 1200 kilometers in radius.however, a recent study put forward the paradox of the nucleation of earth's core, show that contradiction about the formation of the earth's core theory.
kernel nucleation paradox earth
in the past 80 years, scientists already know that there are, a crystallization of the earth's core.but scientists at case western reserve university, points out that the widely accepted view ignores a key point, as long as considering the key point, would suggest that there should be no kernel earth.
it is well known that under a certain pressure, the temperature of the material must be less than or equal to its freezing point temperature to stay solid.but it turns out that when initially formed from liquid metal crystal need extra energy.this additional energy is nuclear energy base, can only overcome this barrier, liquid crystal is possible.initially, however, the formation of the earth's core model without considering this factor.
heterogeneous material can be used as a point of nucleation
in order to overcome the nucleation energy barrier to form crystals, the liquid temperature below freezing point, form a"cold"state.or add some other substance in liquid, making it a point of nucleation, this can reduce into nuclear power base, thus easier to crystallization.
one of the study's lead author dr.steven hauck professor said:"previously, we included all of the people seem to have ignored the problem, the start of the crystallization of liquid metal will not immediately, unless something can greatly reduce the energy barrier."
however, in the center of the earth, under the great pressure of metal into nuclear power base is quite high.core temperature of 5700 degrees kelvin, the pressure is up to more than 300 ten thousand times earth's atmosphere.under this pressure, in order to make the kernel crystallization, need to make the liquid metal temperature below the freezing point(or melting temperature up to 1000 degrees.if the center of the earth to the temperature, almost all of the core should be rapid crystallization, but in fact is not.in fact, the temperature of the earth every 1 billion years to 100 degrees, 1000 degrees so impossible much colder.
as a result, if the core is a homogeneous liquid, so solid kernel should not exist, because it can't be too cold to this extent.so, if the core is not homogeneous liquid, how did it evolve into this?this is the earth's core nucleation paradox.
earth solid kernel may cause
as mentioned above, the liquid crystal or too cold, either need nucleating agent, the former in the earth's core is impossible, only the latter is possible.the research team believes that chunk of solid metal fell from the slowly in the upper mantle of the earth's core, into the liquid core to reduce into nuclear power base, triggering crystallization.however, this requires a large metal pieces, like a big city, only through the mantle, the weight of the big enough to enter the core, make it a point of nucleation, but not completely melt.
is the kernel of the solid earth
this, another scientist professor van orman said:"if it really is the case, we need to figure out what the hell happened.in addition, the core of whether there is something we've never thought of the general characteristics, can make its overcome into nuclear power base?solid earth kernel exists, now we are going to find out exactly how it formed."
at present, the study is published in the"earth and planetary science letters(earth and planetary science letters).