Q 01/05

What force holds Earth's atmosphere to the planet instead of letting the air drift off into space?

A) Magnetism

B) Centrifugal force

C) Air pressure

D) Gravity

Answer · why

D) Gravity

Gravity. The small, hot innermost planet has too weak a pull to do the same job, which is why it is left almost airless.

Q 02/05

Oxygen, dry air's second most abundant gas, is about what percentage?

A) 1%

B) 5%

C) 21%

D) 78%

Answer · why

C) 21%

21%. Almost all of it is a by-product of photosynthesis: before living things began releasing oxygen, the air held practically none.

Q 03/05

After the two dominant gases, which gas ranks third in dry air at nearly 1%?

A) Neon

B) Methane

C) Argon

D) Helium

Answer · why

C) Argon

Argon. Almost all of it was made inside the Earth, by the slow radioactive decay of potassium in rocks, and has been leaking out into the air ever sin...

Q 04/05

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

A) 0.04%

B) 0.40%

C) 4.0%

D) 40%

Answer · why

A) 0.04%

0.04%. Small as that share is, burning fossil fuels had by 2024 pushed it about 50% above its level before the Industrial Revolution.

Q 05/05

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

A) 50 km

B) 100 km

C) 200 km

D) 400 km

Answer · why

B) 100 km

100 km. The round number is a convention: Theodore von Kármán's own sums put the limit of winged flight nearer 84 km, and the US Air Force counts spac...