The diaphragm is the large flat muscle. hope that helps :)
Half-life = time in which half of material is lost
1/4 = 1/2 x 1/2 so 2 half lives have gone by if only 1/4 of it is left.
age of rock = 2 x half life = 2x1.3 = 2.6 billion years.
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Ur welcome ;) (Even tho I uploaded it from the web lol)
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