Q 01/05

What kind of rock is coal?

A) Sedimentary

B) Volcanic

C) Igneous

D) Metamorphic

Answer · why

A) Sedimentary

It forms in layers called seams as buried peat is cooked by heat and pressure over millions of years.

Q 02/05

What do decaying plants become first, before heat and pressure turn them into coal?

A) Tar

B) Peat

C) Shale

D) Charcoal

Answer · why

B) Peat

Most modern peat bogs formed about 12,000 years ago after the last ice age.

Q 03/05

Which geologic period is literally named 'coal-bearing'?

A) Jurassic

B) Devonian

C) Carboniferous

D) Permian

Answer · why

C) Carboniferous

The name comes from the Latin carbo and fero, coined by William Conybeare and William Phillips in 1822.

Q 04/05

Roughly what share of all coal beds were laid down in just two geologic periods?

A) 30%

B) 50%

C) 70%

D) 90%

Answer · why

D) 90%

Atmospheric oxygen above 30% and forests full of slow-rotting lignin helped pile up the peat.

Q 05/05

Which is the highest rank of coal?

A) Anthracite

B) Lignite

C) Sub-bituminous

D) Bituminous

Answer · why

A) Anthracite

It has the most carbon, the fewest impurities and the highest energy density, and is mostly burned for heating.