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Actually, main thing that kelvin got wrong is that the Earth has a liquid mantle. Convection in the mantle means that the surface receives more heat from the in

by ufo 7y ago

Actually, main thing that kelvin got wrong is that the Earth has a liquid mantle. Convection in the mantle means that the surface receives more heat from the interior and takes longer to cool down to the present temperatures. Radioactive decay inside the earth also adds to the age of the earth but not as much as the convection in the mantle does.

tialaramex 7y ago
That's fair, a "convective mantel" model which accepts Kelvin's other assumptions gives 2-3 billion years, so it's at least ballpark compatible with biology. I think you'd have struggled to hide the mismatch eventually but it does pass a laugh test unlike 20 million years. Unlike radioactivity, Kelvin could have considered convection and so that's his fault.
adrianN 7y ago
I don't understand how convection can increase the time to cool down. It seems to me that the higher temperatures closer to the surface facilitated by convection would lead to faster cooling.
- jaggederest 7y ago
  Faster cooling, but smoother gradients. It means that if you go down a hundred miles, it will be warmer, but the entire center of the earth will be closer to the same temperature. If you assume a solid, you assume a certain constant thermal conductivity, as Kelvin did, even though with a liquid, that's not true. Basically, he assumed that the heat was diffusing slowly, and that it couldn't go above a certain temperature at the core (i.e. not a gas or liquid), and so you had hard limits on the total reservoir of heat in the planet and could calculate a linear fit on it. It turns out the effective thermal conductivity of the center of the earth is much higher than the thermal conductivity of e.g. continental crust.
  - im3w1l 7y ago
    > If you assume a solid, you assume a certain constant thermal conductivity, as Kelvin did, even though with a liquid, that's not true I think the liquid is a red herring here. The important thing is a that there are two layers with different properties. Would work just as well with an inner highly conductive solid.
- ufo 7y ago
  WIthout convection the earth as a whole takes longer to cool down but the surface layer cools faster. In an earth with a convective mantle the earth as a whole cools faster but the surface layer cools slower (because it is receiving more heat from the core). This article helped me understand that back in the day: www.blc.arizona.edu/courses/schaffer/449/England%20-%20Perrys%20Neglected%20Critique.pdf
pfdietz 7y ago
The mantle is (mostly) not liquid. It can transmit shear waves, which a liquid cannot do. The convection is occurring in a solid, by plastic deformation. What's sad is that Kelvin could have used his reasoning to determine that this convection must have been occurring, and from that inferred that continents likely drift around, driven by convection. But he was driven by religious convictions to try to demonstrate evolution couldn't have occurred because there wasn't enough time.

by ufo 7y ago

tialaramex 7y ago

That's fair, a "convective mantel" model which accepts Kelvin's other assumptions gives 2-3 billion years, so it's at least ballpark compatible with biology. I think you'd have struggled to hide the mismatch eventually but it does pass a laugh test unlike 20 million years. Unlike radioactivity, Kelvin could have considered convection and so that's his fault.

adrianN 7y ago

I don't understand how convection can increase the time to cool down. It seems to me that the higher temperatures closer to the surface facilitated by convection would lead to faster cooling.

jaggederest 7y ago
Faster cooling, but smoother gradients. It means that if you go down a hundred miles, it will be warmer, but the entire center of the earth will be closer to the same temperature. If you assume a solid, you assume a certain constant thermal conductivity, as Kelvin did, even though with a liquid, that's not true. Basically, he assumed that the heat was diffusing slowly, and that it couldn't go above a certain temperature at the core (i.e. not a gas or liquid), and so you had hard limits on the total reservoir of heat in the planet and could calculate a linear fit on it. It turns out the effective thermal conductivity of the center of the earth is much higher than the thermal conductivity of e.g. continental crust.
- im3w1l 7y ago
  > If you assume a solid, you assume a certain constant thermal conductivity, as Kelvin did, even though with a liquid, that's not true I think the liquid is a red herring here. The important thing is a that there are two layers with different properties. Would work just as well with an inner highly conductive solid.
ufo 7y ago
WIthout convection the earth as a whole takes longer to cool down but the surface layer cools faster. In an earth with a convective mantle the earth as a whole cools faster but the surface layer cools slower (because it is receiving more heat from the core). This article helped me understand that back in the day: www.blc.arizona.edu/courses/schaffer/449/England%20-%20Perrys%20Neglected%20Critique.pdf

pfdietz 7y ago

The mantle is (mostly) not liquid. It can transmit shear waves, which a liquid cannot do. The convection is occurring in a solid, by plastic deformation. What's sad is that Kelvin could have used his reasoning to determine that this convection must have been occurring, and from that inferred that continents likely drift around, driven by convection. But he was driven by religious convictions to try to demonstrate evolution couldn't have occurred because there wasn't enough time.