On 22/02/2021 22:10, Tim Streater wrote:
On 22 Feb 2021 at 21:57:09 GMT, Fredxx wrote:

I thought the issue was more if Earth loses it's magnetic field. Mars
with the lack of a magnetic field is though to have contributed to the
loss of it's atmosphere. High altitude measurements suggest it is an
ongoing process.

Of course Venus lacks a magnetic field, is smaller than earth yet
retains an atmosphere many times than that of the earth. It's upper
atmosphere is said to be Earth-like.

No apo'strophe's needed in any of that.

Agreed, didn't realise I'd put them in.

The magnetic field keeps the solar wind away from the planet. This wind strips
the atmos away, over time.

Venus has/had volcanoes much like the earth, but lacked plate tectonics - not
having been biffed into by a Mars-sized object like the Earth means its crust
is much thicker. So, no life to occupy the non-oceans which meant no building
up of carbonate rocks below the seas. Earth's volcanoes over the aeons are
reckoned to have outgassed as much CO2 as on Venus - 90 Bars worth, but on
Earth life processes have acted to capture nearly all of it.

The biffing the Earth got also meant that the crust melted entirely, allowing
most heavy elements (including the radioactive ones) to sink below the crust.
Their radioactive decay is why the core is molten, just as well as that gives
us the plate tectonics business.

The Venus landscape renews itself every 100-300 million years where the
core accumulates sufficient heat it melts the surface. It is thought
that the lack of water in the crust prevent the formation of plates and
prevent them from slipping.