Sedimentary rocks are useful records of past time because of
1.their unique colors
2.the minerals found in them
3.their volcanic origin
4.their layered structure

Sedimentary rocks are useful records of past time because of their layered structure. Hope this helps!

When a lake, river or other aquatic  system  becomes  eutrophic, it can have serious negative effects on other organisms like fish, birds and even people.if an algal bloom is so bad that it causes wide-spread death  in  the  water, the organisms that die will all sink to the bottom and start to decompose.