Read the following paragraph and answer the question. Give ONLY the answer, no other words or explanation.

For example:

Answer: <most likely answer, as short as possible>.

Paragraph: 
Ozone near the ground harms human health. Ground-level ozone is a pollutant. But the ozone layer in the stratosphere protects us from harmful solar rays. That’s why people were alarmed in the 1980s to learn that there was a hole in the ozone layer.


Question: When did we learn there was a hole in the ozone layer?
1980s
1980s.