Dirt Crawlspace
Mold and mildew grow on organic materials, moisture accelerates this growth.
Post
The posts are rotting out, stacks of wooden blocks have been stacked to try and help support the home.
Mold
You can see the growth is on the ground and on the floor joists. These spores find their way into your home.
Unstable
We see this a lot in crawlspaces. stacking wood is not a good way to support your home. They are unstable and will just rot out like the rest of the posts did.