First life form on earth was a

Options

A. Cyanobacteria
B. Chemohetrotrophs
C. Autotrophs
D. Photoautotrophs

Answer

To determine the first life form on Earth, we can follow these steps:

### Step 1: Understand the Environment
The first life forms are believed to have evolved in an aquatic environment. This setting was rich in organic substances, which played a crucial role in the development of early life.

**Hint:** Consider the conditions of early Earth, particularly the presence of water and organic materials.

### Step 2: Identify Nutritional Modes
The early organisms likely absorbed organic substances from their environment for nutrition. This leads us to categorize them based on their nutritional modes.

**Hint:** Think about how organisms obtain energy and nutrients from their surroundings.

### Step 3: Classify the Organisms
The organisms that absorbed organic substances for nutrition can be classified as chemoheterotrophs. These organisms do not have the ability to fix carbon to create their own organic compounds. Instead, they rely on existing organic molecules.

**Hint:** Recall the definitions of different types of nutrition, especially heterotrophic nutrition.

### Step 4: Understand Chemoheterotrophs
Chemoheterotrophs can be further divided into two categories:
- Chemolithoheterotrophs, which use inorganic energy sources.
- Chemoorganoheterotrophs, which utilize organic energy sources.

**Hint:** Differentiate between the types of heterotrophs based on their energy sources.

### Step 5: Conclusion
Based on the understanding that the first life forms absorbed organic substances and were classified as chemoheterotrophs, we conclude that the first life form on Earth was a chemoheterotroph.

**Hint:** Reflect on the characteristics of the options provided and how they relate to the nutritional strategies of early life forms.

### Final Answer
The first life form on Earth was a **chemoheterotroph**.