Lynn Margulis, a famous evolutionary biologist died recently. Here’s a sentence from an article about her.
She was also a major contributor to the Gaia theory, which posits that Earth is a self-regulating complex system, and was once married to astronomer Carl Sagan.
The rule in English is that you never separate a subject from its verb with an odd number of commas. This sentence has a compound predicate, so you have a subject and verb before you get to the first comma. So the sentence is grammatical as it stands.
I’ll get into this more in a future post about the sin of pretentiousness in writing, but you need to have a comma before “which.” “Which” and what comes after it is really an aside, supplying extra information about the Gaia theory.
After the second comma you find a verb but no subject. What’s the subject? Normally you go back to the first suitable noun, in this case, Earth. Carl Sagan was an unusual person, but I doubt the earth was married to him! That second comma to the rescue—it ends the aside and makes you jump clear to the front of the sentence.She and Carl were married. Still a pretty interesting situation, but at least possible.
Editorial comment: That aside is so long, it somewhat separates the second verb from its subject, even with the comma. Maybe they should have changed that last comma to a period and made a second sentence starting with “She.”