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sickle-cell anemia


a painful, inherited disease that causes red blood cells to
become curved

 

grueling


very demanding and tiring

 

donate


give

 

transplant


an operation in which an organ or other part of the body
is replaced

 

bone marrow


a substance, found inside bones, that makes a body’s
red blood cells

 

fossils


the remains of plants or animals that have been preserved
in rock

 

theories


ideas that try to explain how or why something happens; they
may be based on facts, but are not yet proven

 

minerals


substances found in the earth that do not come from a plant
or an animal

 

excavation


the digging up of an area to find buried remains

 

ice age


a period of time, long ago, when large parts of Earth were
covered with ice