The Bible is the Word of God. Written by man, because God has wonderfully chosen to work through man since He created the dawn of time. How do we know it's the Word of God? Well I suggest you try reading it with the perspective that this is one huge book all about Jesus Christ - God incarnate, man's only hope! Take a step of faith! Expect the living God to speak to you!
Many people seem to think that there are contradictions in the Bible which prove it invalid. An example of which is the following:
'GEN6V3 "THEN THE LORD SAID, "I WILL NOT ALLOW PEOPLE TO LIVE FOREVER; THEY
ARE MORTAL. FROM NOW ON THEY WILL LIVE NO LONGER THAN 120 YEARS."
BUT:
GEN7V6: "NOAH WAS 600 YEARS OLD WHEN THE FLOOD CAME ON THE EARTH"
ADMITTEDLY NOAH WAS MENTIONED BEFORE GEN6V3, BUT AFTER THE FLOOD HE STILL
LIVED ANOTHER 350 YEARS - GEN9V28.
THROUGHOUT GEN11 ALL NOAH'S DESCENDANTS ARE RECORDED AS ALL LIVING LONGER
THAN 120 YEARS AS WELL'
The truth is the people of that age were following their fleshly lusts in their marriages. They were resisting God. However, God in His mercy granted people a reprieve: "yet his days shall be one hundred and twenty years."
The people of this age knew not of everlasting life. This had not yet been revealed to them by God. People like Noah must have had a wonderful surprise when they died!!! This of course leaves us in New Covenant 21st Century Biblically provided post-modern western culture with NO EXCUSE! So the people of Noah's age just thought that life was all about life, and God's judgement would be within life and indeed death itself. God, in His mercy, had promised to grant the people 120 years of deferring His judgement on them. By this He was giving the people time and space to prevent this judgement by their repentance and reformation. In other words, the minimum amount of years anyone had at this time was 120! No wonder many older people are found after this promise was made.
Older people like Noah had repented, and received the Spirit of God for new life in service to Him. Their days were long (present grace), their judgement was taken out on Jesus (penal substitution) who was crucified before the creation of the world (Rev 13:8), and they are still alive now! (future grace)
What can we learn from this? Well the time of God's patience and forbearance towards provoking sinners is sometimes long, but always limited (then it was 120 years - Everything that happened back then was, for His glory, to teach us (1 Cor 10:6-13)). By God handing the people a repreive, He was not pardoning them! God bears with sinners for a great while....but he will not bear always.
I would very much like to answer some of your questions on the truth about life revealed in The Bible.