This week you surveyed many different groups of living things. What Domain of living things is thought to have been the first form of life on Earth? Name one piece of evidence that exists for the claim that these were the earliest living things? Solution Archaea are found in the harshest environments on Earth, and are the oldest known organisms on Earth, appearing in the fossil record over 3.6 BILLION years ago Archaea display unique capacities, such as methanogenesis and survival at temperatures higher than 90 °C, that make them crucial for understanding the nature of the biota of early Earth..