‘90s

[Odessa Dawn]

"Over 800 exoplanets have been discovered since the early ‘90s with many of them having Earth-like traits. The high number of discoveries is making scientists believe that it is more likely extraterrestrial life will be found."

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What is the purpose of the single opening in the underlined part?

[Rover_KE]

If anything, it should be an apostrophe (like a closing inverted comma) signifying the omission of '19' (presumably), though it's normally omitted altogether.

Rover