Answer:
Christians and scientists have different ideas about this.
Christians believe, quite simply, that God created everything on the Earth, from the smallest microorganisms to the gigantic redwood trees and blue whales. Christians refute that life could have occurred just by chance.
Scientists have different theories about the origins of life. Many believe in a "big bang" theory, but there are many different theories out there, most of which have life arising from "spontaneous generation".