Which type of nutrition is believed to have come first?

I believe the type of nutrition that is believed to have come first is Heterotrophic mode of nutrition. Heterotrophic mode of nutrition is a type of nutrition in which animals or organisms depend upon other organisms to survive. All animals and non green plants are heterotrophic organisms. These organisms have to acquire and take in all the organic substances they need  for their survival. 

The basic building blocks of dna and rna are nucleotides