Venerian tectonics

I caught this yesterday afternoon: Venus once had tectonics. Brown University didn't gather that from the uplands of Venus today, if you can call them continents; those are all push-plateaux like Tibet (Maxwell in particular looking like a himalaya). The present state of Venus looks like it was perma-broken by an impact. Brown got their result, rather, from abundance of the gasses in Venus' atmosphere today, namely nitrogen and carbon-dioxide. These developed from starting-points in Venus' distant past.

I don't know if the Brownies used pre-oxygenated Earth as a proxy. Back in 2020, Lehmer and three others got "Atmospheric CO₂ levels from 2.7 billion years ago inferred from micrometeorite oxidation" - those meteorites being dug out from here. 2.7 Gya, our sun was "20% fainter". They mean: at 1.8 Gy after the end of T Tauri, Sol's luminosity was 0.808, from a 2001 paper's Table 2. CO₂ then was over 70% by volume. Although some claim that green "oxygen oases" existed already.

For Earth, though; that earlier team didn't constrain pressure. Did the Brownies constrain pressure on contemporary Venus? I mean, not quite contemporary; they're more going for 4.5-3.5 Gya when luminosity was ranging 72-7%. Venus then would have incurred some 1900s W/m² which is still quite a bit more baked than Earth's 1361 today. If Venereal atmo was CO₂ (with H₂O vapour?), as later Earth suggests, Venus must have been a greenhouse back then too. If the surface was watery that atmosphere must have been thin. If CO₂, then that layer was not liquid.

I am, however, interested to know if supercritical CO₂ can conduct tectonics as water can.