3First of all, you must understand that in the last days scoffers will come, scoffing and following their own evil desires. 4They will say, "Where is this 'coming' he promised? Ever since our fathers died, everything goes on as it has since the beginning of creation." 5But they deliberately forget that long ago by God's word the heavens existed and the earth was formed out of water and by water. 6By these waters also the world of that time was deluged and destroyed. 7By the same word the present heavens and earth are reserved for fire, being kept for the day of judgment and destruction of ungodly men.
This text is future oriented, teaching believers to be certain of Christ's second coming, even in the face of scoffers. However, Peter points to 2 events from the beginning of Genesis, linking their reality to the reality of the second coming. Those events are: the creation of the world by the mere word of God (He spoke it into existence and He did this by dividing the land from the waters, exactly as it is described in Genesis 1) and the destruction of the world by a global flood. It seems clear that Peter believed these events to be historical fact, interpreting Genesis as history and not fable or parable.
Peter also clearly is addressing an argument we now understand as a bedrock of Naturalism - that all things have gone on like they are now since the beginning (if there was one). This is known as Uniformitarianism. Peter tells us that those who deny that there will be a second coming of Christ, and the attendant resurrection and judgment, will also deny the creation and the flood. (Concepts remarkably like modern ideas of evolution existed in some Greek philosophy well before the time of Christ.) Interestingly, Darwin, in his On the Origin of Species, claimed that evolution would inexorably lead to a perfection of humankind that negates the need for Christ's second coming, and, in the same breath, he denies that any cataclysm like the biblical flood has ever occurred. This would also lead to a destruction of any meaningful understanding of Genesis.
"As all the living forms of life are the lineal descendants of those which lived long before the Silurian epoch, we may feel certain that the ordinary succession by generation has never once been broken, and that no cataclysm has desolated the whole world. Hence we may look with some confidence to a secure future of equally inappreciable length. And as natural selection works solely by and for the good of each being, all corporeal and mental endowments will tend to progress towards perfection." Charles Darwin, Origin, p459
Now, the second coming of Christ is an absolute necessity for Christian orthodoxy (and just for the faith to make any sense at all). If we reject His coming, what do we have left? Only an ethical rule for today, but certainly no hope of escape from the grave. (Or possibly some sort of heretical thought in which physical matter is considered evil and it is thought that believers will live on only in spirit after death. However, this has been rejected down through the ages and neglects the fact that man was always meant to live in a body - I'll deal with this issue of the nature of man in another post later.)
Also, if you think on it at all, you will easily see that Christ's second coming will eclipse by far these other two events (creation and flood) in enormity and effect on the world. So, if you hold to orthodoxy and believe in His coming again, what could keep you from believing in the Bible's testimony of these lesser events? It is inconsistent to believe in the one and not the other.