61. The climate could warm enough by the end of the next century to make an eventual collapse of the ice sheet inevitable, he said. 62. The date of these artifacts comes from an era shortly after a mile-long ice sheet had retreated northward from present-day New England. 63. The effects of those ice sheets were soon felt in Africa. 64. The ice sheet is a ledger of the past, a readable frozen history stretching back over half a million years. 65. The ice sheet was long thought to be static and immobile. 66. The great East Antarctic ice sheet, in places three miles thick, was formed after the Pliocene. 67. The larger, more stable East Antarctic ice sheet sits atop a single land mass. 68. The net effect of these competing influences varies from one expanse of ice to another and determines whether an ice sheet gets thinner or thicker on balance. 69. The research involved measurements of sea ice thickness made by upward-looking sonar aboard naval submarines operating under the ice sheet. |