# Is weathering of rock a primary means of $\text{CO}_2$ scrubbing on primordial Earth?

I read somewhere that the reason Venus has a runaway greenhouse effect and Earth doesn't is because Venus failed to develop tectonic plates and instead formed a full tectonic plate enveloping the entire planet. And as such, Venus cannot scrub $$\mathrm{CO}_2$$ from its atmosphere by burying the weathered rock back into the mantle while Earth can, which eventually caused a positive feedback loop of high temperature softening plate preventing fracture which prevents burying of $$\mathrm{CO}_2$$, which puts more $$\mathrm{CO}_2$$ in the atmosphere, which raises the temperature even more. Regardless of the truthfulness of this theory, is the weathering of rock a primary mechanism of $$\mathrm{CO}_2$$ scrubbing on red-hot primordial Earth long before life occurred?

• It would be great if you can add the source where you did read all that. – Camilo Rada Mar 13 '19 at 23:12
• Looks like OP has long given up :-) – user18607 Jan 5 '20 at 20:27

NO, it's not a very major sink on our planet, red is the extra carbon from human activities: https://jancovici.com/en/climate-change/ghg-and-carbon-cycle/wont-the-carbon-sinks-absorb-the-extra-co2/

Cool theory about Venus. It lacks a strong magnetosphere, so the solar wind carries away more light elements like hydrogen, and water vapor, the solar wind has carried away all the seas of venus since about 2 billion years ago, probably aided by the sun being 30% bigger and hotter there.

So, if Venus had kept it's CO2 levels in check, it would probably have sunk them in limestone, and also weathering if there was tectonic activity. Weathering does account for 0.2 to 1 gigaton of CO2 sink every year, compared to 30 gigatons released every year from fossil fuels.

The primary store of carbon in the earth's surface is in limestone, comprising about 60,000,000 gigatons of carbon, and coal and oil. the total amount of carbon near the surface of the earth is source 120 million GtC. Life exists on our planet since about 3.8 billion years, so it could have survived in Venusian oceans until about 2 billion years ago. That's the same time that the first major limestone layers appear on earth about 2.4-2.8 billion years ago. https://www.skepticalscience.com/weathering.html#significance

The Role of Plate Tectonic-Climate Coupling and Exposed Land Area in the Development of Habitable Climates on Rocky Planets cites a few references for the global carbon cycle model.

The diagram on page 8 seems to imply that subduction is the only sink.

• But there's no plate tectonics on Hadean earth, though surely vigorous convection. It starts late in the Archean. Atmosphere of the short phase of a "red hot earth" at the start of the Hadean is pretty unclear ... hydrogen ? shrug Today, yeah, weathering of a Himalaya can be pretty effective ... though slow. – user18607 Jan 5 '20 at 20:28
• Ah, I missed that red-hot part. The intermediate sinks of the same model (direct weathering of silicates by CO2) would still apply, right? – Andris Birkmanis Jan 5 '20 at 22:41
• Probably. You mean so-called "faint young sun paradox" ? – user18607 Jan 6 '20 at 11:57
• Partially. I guess we can improve the original question by spelling out subquestions. I guess the main question is "Why Earth is not as hot like Venus?". – Andris Birkmanis Jan 6 '20 at 17:31
• 1. Was Earth less hot initially and why? This is not as simple as being further away from the Sun, as the initial temperature was set by accretion energy (with internal fission/fusion likely playing some role, too). 2. What was the mechanism for the runaway greenhouse effect on Venus? Was it initially driven by water vapor? For water the positive feedback is pretty obvious, how about for CO2? 3. If CO2 was important for greenhouse effect, how was Earth able to remove it from the atmosphere more efficiently than Venus before Earth developed tectonic plates? – Andris Birkmanis Jan 6 '20 at 18:31