K-T boundary

Noun

The geological signature of the transition between the Cretaceous period and the Tertiary period 65.5 million years ago.

Japanese Meaning

約65.5百万年前に白亜紀から第三紀への移行を示す、地質学上の境界（層状の地層に残された証拠）

Geologists discovered a thin clay layer at the K-T boundary that contained unusually high levels of iridium.

地質学者たちは白亜紀-第三紀境界の薄い粘土層で異常に高いレベルのイリジウムを含んでいるのを発見した。

Sense（1）

The geological signature of the transition between the Cretaceous period and the Tertiary period 65.5 million years ago.

Sense（2）

This transition is marked worldwide by a layer of material that contains a high level of iridium.