I'm sorry this might need background knowledge of economics, which I lack.
1. What does "the gold ever mined still exists" mean? Does it mean every type of gold mined even from 1960s to 1990s still exists, which make them still valuable?
2. This needs some economic theory. I guess money value in real estate and cash can drop down due to inflation or something. So if you had $400,000 of a house, can it be depreciated to $300,000, causing owners seek more gold? Do you know the process of depreciation?

gu72)Everyone knows that gold is valuable, but few people understand how its price is set. For investors, however, it is essential to understand what can influence rising gold prices. As with most investments, the price of gold depends of supply and demand. But the gold market is unique - nearly all of the gold ever mined still exists. Therefore, during times of depression, gold prices rise as people lose faith in money and view gold as an asset that can always be used to purchase necessities. Another common factor influencing gold prices both inside and outside of the country is the real estate market. When real estate values drop, the demand for gold is generally expected to increase.