The Great Depression: Could it happen again?

I fear the entire world is heading for one... The Environmentalist are saying there is only 20 years of oil left! ... on earth all together.. So if we want to keep from heading to depression we better get something that is an alternative into mainstream and fast.... :( ... It's frightening... but it is a reality... We had a market crash in our lifetime but it was not as bad.... however I believe that is a warning that if we do not want to fall into another great depression then precautions need to be taken... and people need to really review their resources...