1. Abiogenesis -- the creation of life from nonlife -- that's the second barrier.

2. ABiogenesis, the idea that life arose from nonlife more than 3.5 billion years ago on Earth. ABiogenesis proposes that the first life-forms generated were very simple and through a gradual process became increasingly complex.

3. Abiogenesis, the idea that life arose from nonlife more than 3.5 billion years ago on Earth. Abiogenesis proposes that the first life-forms generated were very simple and through a gradual process became increasingly complex.