The first organisms that inhabited Earth's surface were bacteria. This is supported by several lines of evidence.

Fossil Record:
The oldest fossils found on Earth are of bacteria-like organisms. These fossils date back to 3.5 billion years ago. These bacteria were anaerobic, which means that they did not require oxygen to survive.

Chemical Evidence:
The chemical composition of rocks that are 3.8 billion years old suggests that they were formed by bacteria. These rocks contain isotopes of carbon that are only produced by living organisms.

Evolutionary History:
Bacteria are the most ancient and diverse group of organisms on Earth. They have been evolving for billions of years and have adapted to almost every environment on the planet.

Autotrophs and Mixotrophs:
Autotrophs are organisms that can produce their own food using energy from the sun or from inorganic compounds. Mixotrophs are organisms that can switch between being autotrophic and heterotrophic (consuming other organisms for food). While these types of organisms are important in the history of life on Earth, they did not appear until much later in evolution.

Chromatotrophs:
Chromatotrophs are bacteria that use chemicals as their source of energy. While these types of bacteria are also ancient, they are not believed to be the first organisms on Earth.

In conclusion, the first organisms that inhabited Earth's surface were bacteria. They have been evolving for billions of years and have adapted to almost every environment on the planet.

Bacteria is first inhabited in earth and so bacteria is heterotroph option C is correct.