 The time was some 480-450 Ma (million years ago), at a period when global paleoclimate was so warm that the planet was all but ice-free.Atmospheric carbon dioxide was fourteen to sixteen times more plentiful than it is today.The Chazy Reef Formation, which built up vertically from a muddy base catching fine dark silt as it grew, began as mounds deposited by bryozoans that stabilized a muddy bottom, then built up into the water column to such an extent that the connected mounds modified their surrounding environment (Mehrtens).