These two organelles support the theory in that both have 70S ribosomes, the presence of a circular DNA within, and similar size. They can undergo division within the eukaryotic cyptoplasm. Both of these organelles are surrounded by a double membrane, which in the case of chloroplast is known to originate from ancient bacteria that lost its peptidoglycan component. Mitochondria and chloroplast both evolved from ancient free living bacteria that entered into larger cells, which in the case of mitochondria is known to be archaea and in the case of chloroplast is a eukaryotic cell. With this, these cells became dependent on it in a manner that it could not exist without it.
There was no life on Earth for the first billion years because the atmosphere was not suitable for life. Earth's first atmosphere had lots of water vapor but had almost no oxygen. Later, frequent volcanic eruptions put several different gases into the air.
A purine is a nitrogenous base found in nucleic acids, and contains a 6-membered pyrimidine ring fused to the 5-membered imidazole ring. The most common examples of purine bases are adenine and guanine.
Thus, the nitrogen base pictured is adenine, and the nucleotide considered is a purine
