So when spacecraft are sent to other planets, scientists will look for layers of gypsum in hopes of finding similar fossils.

VOA: special.2010.05.25

It describes in detail the huge amount of work involved in carefully examining the many layers of tar and earth.

VOA: special.2010.04.07

And,for people that have no written history, language can be one of the ways that that history can be gotten at just by looking carefully at the different layers in the language."

VOA: special.2009.12.02