Based on evidence, scientists believe Earth is over four billion years old. Indirect evidence, such as radioactivity of certain elements found in rocks, as well as direct evidence, such as observations of Earth's rock layers, are used to help scientists make these calculations. Rock formations and the fossils within them can help scientists establish relative ages of major events in Earth's history. Which statement describes the most accurate conclusion scientists can make based on the evidence given? A) Scientists conclude sandstones with ripple marks might indicate a shoreline habitat or a riverbed. B) Upon discovering pieces of cracked limestone, a scientist concludes an earthquake happened in that area. C) After discovering a thick layer of igneous rock, scientists conclude that area was once part of an ocean. D) A scientist discovers a layer of dark metamorphic rock and concludes a volcano had erupted in that location.