Q 01/05

A thin layer of iridium-rich clay found in rocks around the world helped explain the disappearance of which animals?

A) Woolly mammoths

B) Dinosaurs

C) Trilobites

D) Giant ground sloths

Answer · why

B) Dinosaurs

Dinosaurs died out 66 million years ago, just when that clay was laid down. Asteroids carry far more iridium than Earth's crust, so the layer pointed ...

Q 02/05

Iridium is named after Iris, a winged messenger of the Olympian gods and the Greek goddess of what?

A) The dawn

B) The moon

C) The rainbow

D) The harvest

Answer · why

C) The rainbow

The rainbow suited an element whose compounds turned a striking variety of colours as its discoverer dissolved them. The pure metal itself is a plain ...

Q 03/05

A golf-ball-sized cylinder of platinum and iridium, locked in a vault near Paris, defined which unit until 2019?

A) The litre

B) The carat

C) The troy ounce

D) The kilogram

Answer · why

D) The kilogram

The kilogram was simply whatever that one cylinder weighed, for 130 years. Three separate keys were needed to open its vault, and a definition built o...

Q 04/05

Many long-life versions of which small car engine part are sold with a fine tip of iridium?

A) Spark plugs

B) Fuel injectors

C) Piston rings

D) Valve springs

Answer · why

A) Spark plugs

Spark plugs lose a little metal with every spark, and iridium stands up to that erosion far better than most metals. The same toughness makes iridium ...

Q 05/05

A hard iridium tip, first fitted to gold in 1834, became the traditional wearing point of which writing instrument?

A) Ballpoint pen

B) Felt-tip pen

C) Mechanical pencil

D) Fountain pen

Answer · why

D) Fountain pen

Fountain pen makers still call the tipping material 'iridium', though a modern nib seldom contains any. Cheaper hard metals such as tungsten have take...