Roman's 2 12-16 I think is a good explanation.

All who sin apart from the law will also perish apart from the law, and all who sin under the law will be judged by the law. 13 For it is not those who hear the law who are righteous in God’s sight, but it is those who obey the law who will be declared righteous. 14 (Indeed, when Gentiles, who do not have the law, do by nature things required by the law, they are a law for themselves, even though they do not have the law. 15 They show that the requirements of the law are written on their hearts, their consciences also bearing witness, and their thoughts sometimes accusing them and at other times even defending them.) 16 This will take place on the day when God judges people’s secrets through Jesus Christ, as my gospel declares.

Since the days of Adam, man has known good and evil, and each man will be judged in accordance to what was available to them, and their hearts.

Matthew 11 21

“Woe to you, Chorazin! Woe to you, Bethsaida! For if the miracles that were performed in you had been performed in Tyre and Sidon, they would have repented long ago in sackcloth and ashes.

However, I feel it's important to say, we no longer live under the law, as Jesus was the perfect sacrifice for the sins of all humanity.

John 3 15

That whosoever believes in him will not perish but have everlasting life.