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These deposits were believed to be residue of liquid water breaking out of cliffs and crater walls, carrying sediment downhill through the gullies, and later evaporating.

This sentence is the original sentence announced by NASA. The issue here is that one teacher says you can insert "relative pronoun + verb be" before breaking as follows:

These deposits were believed to be residue of liquid water which is breaking out of cliffs and crater walls, carrying sediment downhill through the gullies, and later evaporating.

I don't agree with the teacher because the water in Mars must have evaporated already and "is" is the "present tense".

Also, I don't see any reason why you would want to insert "relative pronoun" before breaking.

I would suggest changing "breaking / carrying / evaporating" as follows if you want to change the present participle into a coordinate or subordinate clause:

These deposits were believed to be residue of liquid water, and it broke out of cliffs and crater walls, carried sediment downhill through the gullies, and later evaporated.

or

These deposits were believed to be residue of liquid water, which broke out of cliffs and crater walls, carried sediment downhill through the gullies, and later evaporated.

What is your opinion on these changes? Thanks.

Sven Yargs
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    Since the form of be in the relative clause is deleted as part of Whiz-Deletion, so is its tense. Consequently no one can ever know whether it would have been is or was; like Schrödinger's cat, it is indeterminate. The rule simply represents an appropriate form of be. Also, the participle phrase is presupposed, since it comes from a relative clause, while joining the clauses by and asserts them instead. That is clearly not the same meaning. – John Lawler Sep 26 '15 at 17:15

1 Answers1

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In the context of the analysis you provide (i.e. evaporation already finished), your instincts are correct and the response you attribute to your teacher is incorrect.

As for your proposed revisions, the second is better as it avoids the broken flow of the first ("and it"). However, the first comma is unnecessary as it turns your phrase into a non-restrictive clause when a restrictive clause is in fact more accurate. (I.e. it's the very water which broke, carried and evaporated that has formed the residue.)

While British English will accept "which" as a relative pronoun here, US styles tend to prefer "that" (and this is also acceptable in BE). The final comma also depends on your style preferences. Thus, a better revision might be as follows.

"These deposits were believed to be residue of liquid water that broke out of cliffs and crater walls, carried sediment downhill through the gullies[,] and later evaporated."

Overall, I find the original sentence preferable as the use of non-finite verbs focuses on the action rather than the water.

Edward Lindon
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