The high degree of carbon in the atmosphere afforded the new land varieties of life opportunity for speedy and luxuriant growth. 
950,000,000 years ago the atmosphere was clearing up, but the amount of carbon dioxide continued large. 220,000,000 years ago the land was overrun by luxurious vegetation; this was indeed the age of ferns. Carbon dioxide was still present in the atmosphere but in lessening degree. 
Much of the carbon of the atmosphere was abstracted to form the carbonates of the various metals which abounded in the superficial layers of the planet.