7.12 Origins of Life on Earth

Describe the scientific evidence that supports models of the origin of life on Earth.

• The origin of life on Earth is supported by scientific evidence.
  • i. Geological evidence reinforces models of the origin of life on Ear th.
  • ii. Earth formed approximately 4.6 billion year s ago (bya). The environment was too hostile for life until about 3.9 bya, and the earliest fossil evidence for life dates to 3.5 bya. T aken together, this evidence provides a plausible range of dates for the origin of life.
• The RNA world hypothesis proposes that RNA could have been the earliest genetic material. There are three assumptions:
  • i. At some point in time, genetic continuity was assured b y the replication of RNA.
  • ii. Base-pairing is necessary for replication.
  • iii. Genetically encoded proteins were not inv olved as catalysts.