Every rock tells a story of Earth

Siim Sepp is a geologist from Estonia who blogs about rocks, minerals, sand and other facets of the world of geology at Sandatlas ( There, you can read about everything from moss-covered lava to a glacier so large it can only be photographed from space.

Q. Your posts explain a lot of geology basics, such as how various kinds of rocks are formed. What do you think most confuses the public about geology?

A. I am not even sure that “confuses” is the right word, but people generally just do not know much about rocks. Lots of people recognize hundreds of species of birds or plants but few are experts in the rocky world. I have tried to give my best to demonstrate that rocks are beautiful and full of interesting stories. This part of geology fascinates me perhaps more than anything else – that there are stories in every rock. It just takes time and practice to learn how to read them.

Q: What are some of the most interesting areas of research underway in geology?

A: A very interesting period in Earth’s history is known as the “Snowball Earth.” During that time, about 650 million years ago, Earth was nearly entirely frozen. This roughly coincides with the time when the oxygen concentration in the atmosphere rose to about the current level and it was also when life forms went through dramatic diversification. It is a crucial and immensely interesting period in Earth’s history that is still relatively poorly understood.

Q: Your blog covers some geological oddities, such as “squeaking sand,” meteorite craters and sandstone mazes. What are a few of the rock, mineral and sand features that are still mysteries to scientists?

A: Geologists are supposed to know a lot about Earth, but we actually know surprisingly little about the interior of our planet. The deepest drill holes penetrate only a very small fraction of Earth. We believe that the outer core is in liquid state. However, the pressure that deep below is so enormous that we may have something else that is not correctly described in terms as liquid or solid. We just don’t know exactly.

Q: You have traveled extensively. Do you have some spots that are your favorites for their geological interest?

A: I really like islands. They are usually interesting geologically because coastal areas have a lot of interesting exposures of rocks. My favorite example may be a bit surprising – Cyprus. There, a relatively small area of land hosts large variety of rock types and geological phenomena.