Final answer:
Bones become brown when exposed and are suitable for fossilization due to their durable nature and ability to last over time, unlike softer tissues that decompose.
Step-by-step explanation:
Bones become brown when exposed with nutrients and minerals; bones make excellent fossils as they can withstand the test of time better than soft tissues. The periosteum layer covering bones provides a shiny appearance, and bones themselves contain bone marrow, necessary for blood cell production. When an organism dies, soft tissues decompose leaving the harder bone tissue behind, which over time may become fossilized and appears brown due to the earthy sediments and the process of mineralization.