Hoth as Earth: the Carbon Cycle before 500MBP

The carbon cycle.

The water cycle is taught to children and is fairly simple and so most people remember it into their adult life.  Basically the water is evaporated from the oceans into the air, the air forms clouds and this causes rain and snow.  The rain fills rivers and the rivers fill the ocean.  Cycle complete.  In later years this cycle is filled out a little more, bringing in ground water and plant transpiration into the mix, but it is still basically the same thing.

The Carbon Cycle is a little more complicated.  On one level, carbon is in the air and is brought into plants.  The plants are eaten and the carbon is released into the air.  Plants decompose, animals decompose and release carbon.  Buried plants and animals turn into fossil fuels, be burn them and release them to the air.  The carbon cycle is already now much more complicated.  Bring in that Volcanoes beltch out a lot of carbon and this carbon comes from the ground, limestone.  Limestone is a sedimentary rock and it relies on water.

Limestone and volcanoes were the only parts of the carbon cycle before the Cambrian Explosion, so for about four billion four hundred million years.  It works like this.  Carbon in the air is Carbon Dioxide.  The carbon in the air is dissolved into the water.  Water and CO2 makes a weak acid, carbonic acid, CO3H2 or 

        OH              O-                    O
OC         ->   OC         ->   OC    Ca
        OH              O-                    O

The acid then stablizes by adding dissolved Calcium to the acid and this forms CaCO3H2, calcium carbonate, which accumulates on the ocean floor as limestone, eventually.  The calcium comes from the land, dissolved from the ground by the rains and rivers.  Calcium carbonate is also formed, after the Cambrian Expolsion, in seashells that make chalk eventually and coral reefs, but limestone was the only way to remove carbon from the air before that time.

Limestone sinks in to the Earth's crust.  The plates subduct into the mantle and volcanoes release the carbon back into the Atmosphere.  Carbon cycle complete prior to half a billion years ago.

Carbon is the driving force in the earth's climate.  There have been at least two world wide ice ages, where the entire earth was covered with two or more kilometers of ice.  This stopped one end of the carbon cycle, with no exposed water, carbon could not enter the oceans and then could not become limestone, but at the same time plate tectonics did not stop and the volcanoes continued to release stored carbon into the air.  This created a run-away greenhouse effect which melted the ice.

This is the nature of cycles, interrupting them often is not a permanent situation.  The Hoth like snowball earth probably lasted millions of years, so it is always a slow process.