In the rocks there were brown layers which came from old riverbeds.
Above this were grey layers made up of lake muds.
These two layers seemed to be evidence for a very wet climate,
but nearby in the same formation there were very different rocks, fossilised sand-dunes.
This was evidence for a very dry climate. It didn't seem to make sense.
You might see one report that said it was desert
and then you might see another report that said it was tropical rainforest in the same place,
but clearly both of those can't be right.
Well you wouldn't think they could both be right
and so it was just sort of trying to figure out what that all meant,
how you could, how these two radically different signals in the same piece of geology that,
that really was one of the things that made this so interesting and surprising.
But as she studied these contradictory signals,
Judy realised there was one answer that would solve the riddle.
The climate had to be two things at once, a hot, dry season and a short but very intense wet season.
This would explain how rivers and deserts could appear at the same time.