does all verbs in a sentance must in the same time?

I know , it must all verbs in a sentance at the same time ; but here is not:
_______ that the American Indian crossed a land bridge into North America from what is now Russia.


1- It is thought
2- it was thoughtthe
best choice is 1 whereas I think the 2 is best because it is past and the time in a sentance is past.

I always confuse with that topic .
thanks in advance

No, Huda, you have the wrong idea. A sentence may have verbs in different tenses. It depends both on the time of each action and on the relationships between the actions.

In your example: ‘It is thought (NOW) that American Indians crossed (A LONG TIME AGO) a land bridge.’