Drilling Into Ancient Rock to Learn About Earth’s Past

Geologists are curious to learn what the Earth was like when the planet was young. We want to know about temperature, beaches, soils, climate, rivers, meteorite impacts, and volcanic activity because these factors determined how and where early life could exist. Only the oldest sedimentary rocks have this information, but these are usually covered by younger rocks. Old sedimentary rocks that still “tell a good story” about the history of the Earth are rare. We studied some of these. They are an unimaginable 3.2 billion years old and are found in the Makhonjwa Mountains near South Africa’s border with Eswatini. We had to drill into the Earth to get to them because the surface is covered by forest and grassland. Sedimentary rock layers in these mountains do not lie flat anymore but are vertical, and sometimes even flipped over. To drill through as many layers as possible, we had to drill sideways!