Q 01/05

Where does more water evaporate than falls back as rain or snow?

A) Oceans

B) Rainforests

C) Ice caps

D) Mountains

Answer · why

A) Oceans

Oceans: they give up about 86% of the world's evaporation but catch only about 78% of its rain and snow. Winds carry the surplus over land, and rivers...

Q 02/05

What powers the water cycle?

A) Solar radiation

B) Earth’s rotation

C) Ocean tides

D) Volcanic heat

Answer · why

A) Solar radiation

Solar radiation: the sun's heat lifts water into the air as vapour, then gravity takes over, pulling it back down as rain and snow and draining it dow...

Q 03/05

After evaporating, about how long does water typically stay in the atmosphere?

A) 9 hours

B) 9 days

C) 9 weeks

D) 9 months

Answer · why

B) 9 days

9 days: all the vapour in the sky would cover the globe only about an inch deep, yet roughly a metre of rain falls each year, so the air is emptied an...

Q 04/05

Deep groundwater that rain no longer refills, like the store beneath the Sahara, goes by what name?

A) Hard water

B) Fossil water

C) Heavy water

D) Grey water

Answer · why

B) Fossil water

Fossil water: Libya's supply soaked in before the last ice age ended, when the Sahara was far wetter. Crews drilling for oil struck it in the 1950s, a...

Q 05/05

Each year, how does the world's precipitation compare with its evaporation?

A) Half as much

B) About the same

C) Twice as much

D) Far more

Answer · why

B) About the same

About the same: some half a million cubic kilometres rise and fall each year, and the sky can never bank the difference, because at any moment it hold...