Ancient Brachiopod Fossils Reveal How Hot Earth’s Oceans Were Half A Billion Years Ago

Measuring what sea temperatures were during the Cambrian Period is an impossible task unless you rely on proxy data. That’s exactly what a team of researchers has done in a new study, published yesterday in Science Advances.

The international team, led by the University of Leicester in the U.K., investigated Earth’s climate from more than half a billion years ago by looking at fossil shells found in England’s West Midlands.

According to Science Daily, the researchers combined chemical analyses of the fossils with climate models to gauge the temperatures of Earth’s oceans 540 million to 490 million years ago — also known as the Cambrian Period.

What they discovered was that, during the early Cambrian, our planet’s climate was in a “typical” greenhouse state, similar to the ones from the late Mesozoic and early Cenozoic eras.

For the first part of their research, the scientists traveled to Shropshire in the U.K. and extracted brachiopod fossils from the area’s iconic limestone. These tiny fossils, dated to between 515 and 510 million years old, were analyzed using electron microscopy, which enabled the team to study their oxygen isotope ratios — “a commonly used paleothermometer,” notes study lead author Thomas Hearing, from the University of Leicester.

“Many marine animals incorporate chemical traces of seawater into their shells as they grow. That chemical signature is often lost over geological time, so it’s remarkable that we can identify it in such ancient fossils,” explains study co-author Dr. Tom Harvey, Hearing’s colleague at the university’s School of Geography, Geology, and the Environment.

Chemical analyses of the millimeter-long brachiopod fossils revealed that high latitude sea temperatures were surprisingly high during the Cambrian and ranged between 20 and 25 degrees Celsius (or between 68 to 41 degrees Fahrenheit).

The team then performed climate model simulations for the early Cambrian, which confirmed the results of the fossil analysis.

“Our results support an early Cambrian greenhouse climate comparable to those of the late Mesozoic and early Cenozoic,” the authors write in their paper, which Hearing hopes will help “build up a clearer picture of ancient climates” for other scientists who don’t have access to conventional climate proxy data.

In addition, the study helps us better understand the early animals that emerged during the Cambrian and shed more light into the environment in which they lived, Science Daily notes.

This particular time in Earth’s history is known as the “Cambrian explosion” and has given rise to most of the major animal groups on the planet. This includes the earliest arthropods, such as the brachiopods used for this study and the trilobite fossil recently found in Tennessee by an 11-year-old girl.