How far back in time are we going? Well, at our last drilling site, the oldest sediments were over 30 million years old. That is about halfway back to the time of the dinosaurs!
So how do we collect clues from the sediments? Well, the first thing I do is look at the sediment. In fact, when I take my college students out on field trips, often the students are a little unsure how to describe the rocks in front of them. So, the first thing I tell them is to try not to describe the rocks as a geologist might, but rather as an average person would, which typically means describing the color of the rocks. When I lay out the sediment cores in front of me, I first look at the colors of the sediments and how they change, which can tell us a lot about what makes up the sediments.
For example, if they are whitish, the sediment is mainly composed of tiny shells made by one-celled creatures. These shells are so tiny that 100 of the shells could line up in a row, and they would STILL fit within one millimeter. (Go check out a metric ruler and see how small one millimeter is.) I then take a little bit of the sediment using a toothpick and look at it under a regular hand lens. I also feel the sediment, which lets me know how much clay is in it. If you can roll the sediment, then there is clay. If you cannot roll the sediment, then there is no clay. Although the shells are tiny, I also look for larger shells, which are the size of a grain of sand. Afterward, we place the cores through special instruments that can tell us the number of magnetic properties, including their exact color.
So why do we collect all this information like detectives? We do this to figure out the past environmental changes that occurred millions to tens of millions of years ago.
