Question

1st life on earth was
A) Cyanobacteria
B) Chemoheterotrophs
C) Autotrophs
D) Photoautotrophs

Answer 1

Hint: Earth was formed almost 3.8 billion years ago and at the beginning of the earth, the environment was very hot with extreme temperatures, and no gases like O2 and Co2 and there were no organic molecules at that time.

Complete answer:
Life on the earth was started some billions years ago, on average it was 3.8 billion years, before that there was no life on the earth, and no biomolecules was found, and after some years there are some chemical changes that was happened on the earth that leads to formation of some organic molecules such as proteins, nucleic acids and all where this leads to the formation of biomolecules such as genes, that are DNA and RNA.
At that time there was no oxygen and carbon dioxide was found on the earth, the biomolecules that lead to the formation of primitive life, and they are autotrophs, but at that period, as there was no carbon dioxide to obtain the organic products, they utilize the chemical substances such as iron, sulfur, and magnesium, etc and this process was called as chemo synthesizes and the organisms are called as chemoautotrophs.
And there are also heterotrophs which depend on the autotrophs and these organisms are anaerobic as the earth does not have oxygen at that time, as these organisms are dependent on chemoautotrophs those are called as anaerobic chemoheterotrophs.
Later after so many years there was development of some gases on the earth, and this led to the production of first photoautotrophs, where they are called as blue green algae, slowly there was development of little developed organisms.

The correct option is B.

Note: The first genes are produced and later that lead to the development of chemoautotrophs as they do not have oxygen and $Co_2$ at that time and the heterotrophs which were present at that time was called as chemoheterotrophs so from the order of given options if is the first one that was formed on earth.