Tiny fossils unlock clues to Earths climate half a billion years ago

An international collaboration of scientists, led by the University of Leicester, has investigated Earth’s climate over half a billion years ago by combining climate models and chemical analyses of fossil shells about 1mm long.

The research, published in Science Advances, suggests that early animals diversified within a climate similar to that in which the dinosaurs lived.

This interval in time is known for the ‘Cambrian explosion’, the time during which representatives of most of the major animal groups first appear in the fossil record. These include the first animals to produce shells, and it is these shelly fossils that the scientists used.

Thomas Hearing, a PhD student from our School of Geography, Geology and the Environment, explained: “Because scientists cannot directly measure sea temperatures from half a billion years ago, they have to use proxy data – these are measurable quantities that respond in a predictable way to changing climate variables like temperature. In this study, we used oxygen isotope ratios, which is a commonly used palaeothermometer.

“We then used acid to extract fossils about 1mm long from blocks of limestone from Shropshire, UK, dated to between 515 – 510 million years old. Careful examination of these tiny fossils revealed that some of them have exceptionally well-preserved shell chemistry which has not changed since they grew on the Cambrian sea floor.”

Analyses of the oxygen isotopes of these fossils suggested very warm temperatures for high latitude seas (~65 °S), probably between 20 °C to 25 °C.

To see if these were feasible sea temperatures, the scientists then ran climate model simulations for the early Cambrian. The climate model simulations also suggest that Earth’s climate was in a ‘typical’ greenhouse state, with temperatures similar to more recent, and better understood, greenhouse intervals in Earth’s climate history, like the late Mesozoic and early Cenozoic eras.

The research was covered by national media outlets including the Independent, the Daily Mail and Sky News.

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