<P> The growth of the inner core may be expected to consume most of the outer core by some 3--4 billion years from now, resulting in a nearly solid core composed of iron and other heavy elements . The surviving liquid envelope will mainly consist of lighter elements that will undergo less mixing . Alternatively, if at some point plate tectonics comes to an end, the interior will cool less efficiently, which may end the growth of the inner core . In either case, this can result in the loss of the magnetic dynamo . Without a functioning dynamo, the magnetic field of the Earth will decay in a geologically short time period of roughly 10,000 years . The loss of the magnetosphere will cause an increase in erosion of light elements, particularly hydrogen, from the Earth's outer atmosphere into space, resulting in less favorable conditions for life . </P> <P> The energy generation of the Sun is based upon thermonuclear fusion of hydrogen into helium . This occurs in the core region of the star using the proton--proton chain reaction process . Because there is no convection in the solar core, the helium concentration builds up in that region without being distributed throughout the star . The temperature at the core of the Sun is too low for nuclear fusion of helium atoms through the triple - alpha process, so these atoms do not contribute to the net energy generation that is needed to maintain hydrostatic equilibrium of the Sun . </P> <P> At present, nearly half the hydrogen at the core has been consumed, with the remainder of the atoms consisting primarily of helium . As the number of hydrogen atoms per unit mass decreases, so too does their energy output provided through nuclear fusion . This results in a decrease in pressure support, which causes the core to contract until the increased density and temperature bring the core pressure into equilibrium with the layers above . The higher temperature causes the remaining hydrogen to undergo fusion at a more rapid rate, thereby generating the energy needed to maintain the equilibrium . </P> <P> The result of this process has been a steady increase in the energy output of the Sun . When the Sun first became a main sequence star, it radiated only 70% of the current luminosity . The luminosity has increased in a nearly linear fashion to the present, rising by 1% every 110 million years . Likewise, in three billion years the Sun is expected to be 33% more luminous . The hydrogen fuel at the core will finally be exhausted in five billion years, when the Sun will be 67% more luminous than at present . Thereafter the Sun will continue to burn hydrogen in a shell surrounding its core, until the luminosity reaches 121% above the present value . This marks the end of the Sun's main sequence lifetime, and thereafter it will pass through the subgiant stage and evolve into a red giant . </P>

Will the amount of hydrogen in our sun increase or decrease over the next few million years