For some scientists, an academic career can feel like crawling into a tower of crap. For other scientists, an academic career actually involves crawling into a tower of crap.

Since 1928, thousands of chimney swifts have roosted at Fleming Hall, a university building in Kingston, Ontario. For decades, they fed on local insects, and excreted the remains down one of the building’s chimneys. Around 2 centimetres of droppings, or ‘guano’, built up every year until the chimney was finally capped in 1992. To this date, Fleming Hall contains a hardened guano tower, two metres tall and 64 years in the making, which preserves a layered record of the swifts’ meals.

Now, a team of scientists, led by Joseph Nocera, have used