Every day Bridget Wade looks into a microscope. She sees very old shells from the sea. They come from animals that lived millions of years ago. Wade also works with students from many countries. She never planned this job. She wanted to study English literature at university, but her grades were not good enough. Now she says this was the big moment of her life. She still reads and writes every day.
The shells come from planktonic foraminifera. These are very small sea animals with only one cell. They are about as big as a grain of sand. When the animals die, their shells fall down and make thick layers on the sea floor. Scientists drill into these layers and study them. The shells tell us about old seas, about hot times and cold times.
Many of these shells are coiled, like a small snail. Some species always coil to the left, and some always coil to the right. But sometimes a species changes direction. Scientists first saw this about seventy years ago. In 1959 David Ericson looked at shells from the North Atlantic. In cold times the shells coiled left, and in warm times they coiled right. He thought the reason was temperature.
Later, other scientists showed that this idea was wrong. In 2013 Yurika Ujiié studied shells from many oceans. The direction did not follow the temperature.
Then Wade and her team looked at old counts from fifty years of work. They studied shells from the last 56 million years. They found something surprising. Species changed direction at the same time in the Atlantic, the Indian and the Pacific Ocean. One species, Pulleniatina obliquiloculata, changed direction every few thousand years all over the world. Wade said she was very surprised, because a local change would be easier to explain.
Wade thinks one hidden group of animals got better and spread everywhere. It is a little like a Covid-19 variant. Kate Darling agrees, but Ujiié is not sure. Julie Meilland grows these animals in her lab in France. Her results are not always the same as the fossils. She said the answer may be genes, the environment, and also luck.