List the two main propositions of Oparin and Haldane.

Explanation

To answer the question about the two main propositions of Oparin and Haldane, we can break down the information into clear steps:

### Step-by-Step Solution:

1. **Understanding the Context**: Oparin and Haldane were scientists who proposed theories about the origin of life on Earth. Their work focused on how life could arise from non-living chemical substances.

2. **First Proposition**:
- Oparin and Haldane proposed that life originated from pre-existing non-living organic molecules.
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