On a mild summer day just outside of Copenhagen, Denmark,
a woman sits in her garden surrounded by oatmeal boxes.
Stored within are hundreds of cards containing handwritten notes which would be incomprehensible to most.
But for the woman pouring over them, one card at a time,
this is the key to finding out what lies thousands of kilometres beneath her feet.
I'm Ella Hubber.
And I'm Julia Ravey.
We're both scientists turned radio presenters.
And these are the stories we wished we'd known when we were starting out as scientists.
This is Unstoppable for Discovery on the BBC World Service.
Julia,
today I'm going to tell you the story of how one woman with a keen eye for detail and apparently magical mathematical abilities challenged the theory of what is at the centre of the Earth.
And she did it in her spare time.
Her name was Inga Lehman.
Right, so where are we starting today, Ella?
Let's start with a quote.
I may have been 15 or 16 years old when, on a Sunday morning,
I was sitting at home together with my mother and sister and the floor began to move under us.
The hanging lamp swayed.
It was very strange.