Q 01/05

By volume, roughly 78% of dry air is which gas?

A) Nitrogen

B) Argon

C) Hydrogen

D) Oxygen

Answer · why

A) Nitrogen

It became the dominant component of Earth's 'second atmosphere' about 3.4 billion years ago, long before oxygen showed up.

Q 02/05

About what percentage of dry air is oxygen?

A) 35%

B) 65%

C) 21%

D) 50%

Answer · why

C) 21%

That share is not fixed forever: it has swung over the past 600 million years and once peaked around 35%, high enough to feed giant dragonflies.

Q 03/05

After the two dominant gases, what is the third most abundant gas in dry air?

A) Carbon dioxide

B) Water vapor

C) Neon

D) Argon

Answer · why

D) Argon

At 0.93% it outweighs CO2 more than twenty to one. Neon, helium and krypton are also present in trace amounts.

Q 04/05

CO2 makes up roughly what fraction of dry air by volume?

A) 4.0%

B) 0.04%

C) 0.40%

D) 14%

Answer · why

B) 0.04%

Small as it is, that trace of CO2 with water vapor keeps the surface roughly 33 °C warmer than it would otherwise be.

Q 05/05

At what altitude is the Kármán line, the conventional edge of space?

A) 200 km

B) 50 km

C) 100 km

D) 400 km

Answer · why

C) 100 km

Theodore von Kármán actually calculated an aeroplane flight limit of 83.8 km; the round-number line above it was fixed in the 1960s and has no distinc...