The first sentence should be like this "I think I would be safe if I come to Earth." I think there is no need of "the". #2- "At that time I thought I would be safe if I came to Earth" thankyou. (correct me if wrong)
I disagree with shawez. I believe that the first sentence is correct. If you wanted to switch "came" to "come", you would have to change "would" to "will" as well:
"I think I will be safe if I come to Earth."
Note that I also removed "the" before "Earth" and capitalized "Earth" as well. Earth, in this case, if a proper noun, referring to the planet, not the ground, so it must
Did you mean to write this sentence in conditional construction? It will depend on what exactly you intend to do. Condition 1: I think I will be safe, if I come. Helpful link: http://www.edufind.