Romans 1:19 - 1:21
19 because that which is known about God is evident within them; for God made it evident to them. 20 For since the creation of the world His invisible attributes, both His eternal power and divine nature, have been clearly seen, being understood through what has been made, so that they are without excuse. 21 For even though they knew God, they did not glorify Him as God or give thanks, but they became futile in their thoughts, and their foolish heart was darkened.
Romans 2:14 - 2:15
14 For when Gentiles who do not have the Law naturally do the things of the Law, these, not having the Law, are a law to themselves, 15 in that they demonstrate the work of the Law written in their hearts, their conscience bearing witness and their thoughts alternately accusing or else defending them,