World Geography
The major events of Pre-Cambrian era include

formation of present day atmosphere
formation of crust, birth of oldest known rock, origin of life
formation of crust, continents and oceans
All of these

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World Geography
The Penumbra is

formed by the tangent that intersects between the sun and the moon
both (a) and (b)
None of these
the outer portion of the moon's shadow

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