| Answer | Crossword Clue |
|---|---|
| COLOSSEUM | Structure dating from 72 A. D. |
| stromatolite | a rounded, multi-layered structure, found in rocks dating back at least 2800 million years, having present-day equivalents that result from the growth, under special conditions, of blue-green algae |
| stromatolites | STROMATOLITE, a rounded, multi-layered structure, found in rocks dating back at least 2800 million years, having present-day equivalents that result from the growth, under special conditions, of blue-green algae |
| MUSLIMERA | Religious period dating from A.D. 622 |
