The composition of the early atmosphere of the Earth was dominated by
A) hydrogen (H2)
B) nitrogen (N2)
C) carbon dioxide (CO2)
D) oxygen (O2)
C
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Observations in the infrared have detected dusty nebulae around T Tauri stars
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The mass of 6 million atoms of a diatomic gas is 
What is the atomic mass of this gas?
A. 25.5 u B. 51.0 u C. 2.55 u D. 5.10 u
While yet unseen, some gravitational evidence suggests the existence of dark galaxies
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What is an alpha particle?
a. A hydrogen atom. b. A helium atom. c. A hydrogen atom without its electrons (and therefore having one unit of positive charge). d. A helium atom without its electrons (and therefore having two units of positive charge). e. A deuterium nucleus (with one proton and one neutron).