Up until about 2 billion years ago, the sun was 30 percent dimmer than it is now. If the sun were that dim now, our oceans would be completely frozen. According to fossil evidence, however, life and liquid water were both present as early as 3. 8 billion years ago. Which one of the following, if true, most helps to resolve the apparent discrepancy described above? ['Evidence suggests that certain regions of ocean remained frozen until much more recently than 2 billion years ago.', 'Our atmosphere currently holds in significantly less heat than it did 3. 8 billion years ago.', "When large portions of the globe are ice-covered, more of the sun's heat is reflected and not absorbed by the earth than when only the poles are ice-covered.", 'The liquid water present 3. 8 billion years ago later froze, only to melt again about 2 billion years ago.']