The first living organisms were presumably................. and heterotrophs, some of which might have evolved into …................... and autotrophs,

Explanation

**Step-by-Step Text Solution:**

1. **Understanding the Environment of Early Earth:**
- The early Earth had a primitive atmosphere that was reducing, meaning it lacked oxygen. This environment was crucial for the emergence of the first living organisms.

2. **Identifying the First Living Organisms:**
- The first living organisms are believed to be **anaerobic**. Anaerobic organisms can survive in environments devoid of oxygen.

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