Now here's a weird thing - when plants do photosynthesis, they prefer to suck in carbon 12, and so this leaves a slight excess of carbon 13 in the environment. So if you dig down in the dirt, and look at the ratios of carbon 12 and 13, you can work out how many plants are doing photosynthesis. Well, it's because 700 million years ago, the continents were all clustered around the Equator. This is quite different from the situation we have today, where there are continents scattered mostly over the whole planet. Well, continents have an on-going contract with that famous Greenhouse Gas, carbon dioxide.
Continents help take carbon dioxide out of the atmosphere.
Clouds form over mountains, and rain falls down through the atmosphere - and as it falls, it dissolves carbon dioxide and dumps it into the ocean. So rain helps take carbon dioxide out of circulation. But rain also falls on stony ground, and weathers the rocks - and this, carbon goes into the ocean as carbonate rocks. So continents take carbon dioxide out of the atmosphere. But they don't do this when they're covered with ice - look at Greenland.