Parallel structure

[sumeettak]

This is a made up from ans. choice of question similar to #8 of OG Sentence Correction. The below is the corrected sentence after applying the correct answer.

The widely accepted theory holds that the solar system began in an explosive instant billions of year ago and has been expanding ever since.

I am trying to understand whether verb form "began" and "has been expanding" on either side of parallel marker "and" are considered as parallel structure. Note that the former is Simple Past and the latter is Past Perfect. If not, will it make the above sentence incorrect ?

Also trying to understand if there is a reason because of which I should avoid looking for parallelism in this sentence ?

[piccolino]

Chronology?!

[mschwrtz]

Parallel verbs need not have the same tense. Even the parts of a compound verb need not have the same tense. For instance, "Sam has studied diligently and will do well." No trouble, the studying and the doing well happen at different times, so different tenses are appropriate.