Adam as first human and prophet?

My question is about Adam (AS). 1) How do we know Adam(AS) as the first person of a upbringings even mentions in Quran that Adam (AS) was the first human being? 2) If Adam (AS) is a messenger of Allah, then who are their Followers? Because Prophets send to a group of people. 3) Quran mention Adam (AS) as a Khalifa but I never saw in Quran He was mentioned as a first human too (May be I am wrong). These question has no any intention about Islam, just ask for knowledge sake.