Our previous page showed that Venus does not exhibit global plate tectonics as seen on Earth. However, it does have a very young surface. How was the planet re-surfaced without plate tectonics?
Currently, Venus is showing quite minimal activity, and has since it was re-surfaced 500 m.y.a. However, Venus might also show periods of extreme, catastrophic activity. What might cause such a sudden instability to develop?
Which dominates: increased or reduced mantle viscosity?
Maybe both, but at different times. Perhaps the mantle can absorb a lot of heat, until
it reaches a critical stage and suddenly undergoes vigorous, global convection. This
would devastate the entire surface all at once. Large scale lava flows, faults
and volcanos, would cover the entire planet. The heat, however, would be quickly
lost with all this surface lava, and then the planet becomes dormant again.
What about the Venusian Atmosphere?
There are some very important chemical reactions occurring between the surface rocks
and the atmosphere, which determine atmospheric conditions (Temp, pressure and
chemistry). They involve the two important greenhouse gases, CO2 and
SO2. If these gases react and become deposited in the rocks, this could
substantially reduce the greenhouse effect by reducing their abundance (pressure)
in the atmosphere. It's also possible that an instability would drive the surface
to an even HOTTER and HIGHER pressure environment than it is!
What initiates a possible instability (to cooler or hotter)? VOLCANISM
Right now, Venus is rather dormant. However, 500 m.y.a., it experienced extreme
volcanism. This would drastically alter the amount of CO2 and SO2
in the atmosphere. This would push surface reactions away from current conditions
of 750 K and 90 bars.. Possibly making it worse, or possibly to a
nicer climate!
With no active volcanism today, Venus has achieved equilibrium. However, this equilibrium could be disturbed and lost should global volcanism begin again.