Bridget Wade works with a microscope. A microscope makes very small things look big. Every day she looks into it. She sees very old shells from the sea. The shells are millions of years old. Wade also works with students. She says the students are the best part of her job. Wade did not plan this work. She wanted to study English books at university, but her school marks were too low.
The shells come from plankton. Plankton are very small sea animals. One animal is as small as a grain of sand. The animals die and the shells fall down. They fall on the floor of the sea. There they make a very long record of old time.
Many shells turn like a snail. Some turn to the left. Some turn to the right.
Wade and her team looked at shells from three big oceans: the Atlantic, the Indian and the Pacific. They saw something strange. Many shells changed direction at the same time in all the oceans. One kind of plankton is called Pulleniatina obliquiloculata. It lives today too. For 860,000 years its shells turned to the right. Before that time, the shells changed direction every few thousand years. Wade said this was a big surprise, because a small local change is easier to understand. But the change was not local. It happened everywhere.
Why? Wade thinks there are hidden kinds of plankton in the sea. One kind becomes strong and takes the place of another kind. Kate Darling is a scientist too. She said the change means new kinds of plankton. Julie Meilland is a scientist in France. She grows plankton in her lab. Her shells do not always turn the way the old shells did. She said genes, the sea and also luck can all be important.