Almost all fossils are preserved in sedimentary rocks , rocks that formed when layers of sediment such as clay, mud, silt, or sand became compressed and hardened over millions of years.
(Almost all fossils; are preserved; L:in sedimentary rocks) (rocks; formed; T:when layers of sediment such as clay, mud, silt, or sand became compressed and hardened over millions of years) (layers of sediment such as clay, mud, silt, or sand; became compressed; )
Almost all fossils rocks layers of sediment such as clay, mud, silt, or sand
are preserved formed became compressed
L:in sedimentary rocks
T:when layers of sediment such as clay, mud, silt, or sand became compressed and hardened over millions of years