What's the appropriate tense here? [duplicate]

I know the past tense carries the past tense in every dependent clause, but referring specifically to places or to things that are eternal, like the Earth, seems a bit weird and therefore we sometimes (I believe incorrectly) say

He didn't know that New Jersey was actually on the East Coast.

Because it still is. Or

He thought the Earth was round.

So is it square now?

Logically speaking, would you consider the use of past tense here a bit confusing in a day-to-day speech in these examples? Would you instinctively opt for using the present tense?

Both tenses are OK, but I believe the past tense is a bit more common: it may be somewhat contrary to logic, but it sounds better. Harmony of tenses (if that's what it's called) is a linguistic phenomenon that is not always very logical.

The clauses that New Jersey was actually in the East Coast and the Earth was round are known in functional grammar as 'projected clauses'. They behave in the same way as clauses that contain what is known in traditional grammar as 'reported speech'. As the authors of the ‘Longman Grammar of Spoken and Written English’ explain:

Simple past tense has a special use in reported speech or thought. The original speech or thoughts may have been in present tense, but past tense is usually used for the reports . . . Notice that the circumstances may still be continuing even though past tense is used (My emphasis).