[thedoc (OP)]

Paul James  asked the Naked Scientists:
   Hi Chris, Paul here from Malaysia. Naked Scientists is my favorite podcast and think it's great the show is free and hope it always will be.
My question is which is the following events will most likely cause the end of life on earth first.
1: When the sun becomes a red giant 2: when the inner core of our planet completely cools and the magnetic field disappears.
Kind regards,

Paul

   
What do you think?

[chiralSPO]

I believe that the sun will go red first. There are two reasons that the core is so hot:

1) residual heat left over from earth condensing and fractionating (heat from heavy stuff falling/sinking to core)

2) radioactive decay

The most of the heat from the 1st process was generated more than 4 billion years ago, and it is still cooling off (presumably taking billions more years to do so). The second is generating a significant amount of heat continuously, much of it derived from radioactive decay of uranium 238 (half life 4.4 billion years) and thorium 232 (half life 14 billion years). So the output of the nuclear decay will also last several billion years more.

The sun is expected to go all red gianty in about 5 billion years

[RD]

The sun is expected to go all red gianty in about 5 billion years

But water all will go in <2 billion years ... http://www.sciencemag.org/news/2014/01/earth-wont-die-soon-thought

Dry would be sufficient to extinguish life , [ in 5 Gyr it will be BBQ'd ].