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Tiny fossils reveal secrets about Earth’s climate half a billion years ago

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Sea fossils as long as one millimetre have unlocked climate secrets of the period known as the Cambrian explosion, when the first animal groups appeared.

Reflected light microscope images of some of the brachiopod fossil

s used in this study

Reflected light microscope images of some of the brachiopod fossil

s used in this study

Reflected light microscope images of some of the brachiopod fossils used in the study

Using data from such fossils and climate models, an international team of scientists led by the University of Leicester have measured sea temperatures on Earth half a billion years ago to be more than 20°C.

The research published in Science Advances on May 9 proposes that early animals appeared and diversified in a climate that is quite similar to the one during which dinosaurs thrived.

The earliest animals appear in fossil records from 570-500 million years ago, the period known for the “Cambrian explosion”. Those include the first animals to produce shells, which now hold valuable data from that era.

 Electron microscope images of some of the brachiopod fossils used in the study

The early Cambrian period has long been believed to be a greenhouse interval in Earth’s climate history, when there has been no polar ice caps. Up until now, scientists used rocks which were deposited at that time to get an idea of the climate, and as such, specific details on the climate have remained a mystery.

Data from the tiny fossil shells and new climate models runs have shown that high latitude sea temperatures were 20°C and above, similar to more recent, better understood, greenhouse climates like that of the Late Cretaceous Period.

The oxygen isotopes of these fossils suggest very warm temperatures for high latitude seas, probably between 20°C to 25°C. To test this hypothesis, the team ran climate model simulations, which suggested Earth’s climate was a 'typical' greenhouse state at the time. Temperatures at the time were similar to other more recent, and better studied, greenhouse periods in Earth's climate history, like the late Mesozoic and early Cenozoic eras.

These findings have helped us better understand the earliest animals and the environment in which they lived.

The research was carried out by an international collaboration involving scientists from the University of Leicester (UK), British Geological Survey (BGS; UK), and CEREGE (France). Experts in geochemistry, palaeontology and climate modelling came together to tackle this longstanding question.

The paper is publicly available in the journal Science Advances.

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