Geologists study Earth and its history. Our planet is mainly made up of rocks and water, both of which are important in the work of a glacial geologist. Glaciers form when unmelted snow becomes increasingly dense over hundreds of years. They can become parts of ice sheets, huge collections of glacial land ice that cover more than 50,000 square kilometers (over 20,000 square miles). Glacial Geologist Lauren Miller Simkins studies ancient glaciers and ice sheets. Knowing more about how ice behaved on Earth’s surface in the past can help us better understand what it’s doing now and what we can expect in the future.