Looking through a powerful microscope, the researchers were amazed to see the impressions left by the single-celled plankton or the fossilized nanoplankton, which lived millions of years ago – especially since they were analyzing something else.
“The discovery of ghost fossils was a complete surprise,” said study author Sam Slater, a researcher at the Swedish Museum of Natural History in Stockholm.
“We were actually studying fossil pollen from the same rocks. I had never seen this style of fossil conservation before and the discovery was doubly surprising because the fingerprints were found in abundance on rocks where normal nanofossils are rare or completely absent.”
As researchers examined the pollen under a scanning electron microscope, they found “tiny pits” on the pollen surface, Slater said. When they zoomed in to see the puddles using magnifications thousands of times, they noticed complex structures.
These structures were the impressions left by the exoskeletons of nanoplankton called coccolithophores.
This tiny plankton still exists today and supports marine food tissues, provides oxygen and stores carbon in seabed sediments. A cobblestone surrounds its cell using a cobblestone, or hard limestone slab, which can be petrified into rocks.
Although tiny as individuals, cobblestones can produce clouds that look like clouds in the ocean that can be seen from space. And as soon as they die, their exoskeletons are dragged down to rest on the seabed. As they accumulate, the exoskeletons can turn into rocks like chalk.
Ghost fossils were created as the sediments of the seabed turned to rock. Layers of mud piling up on the seabed pressed hard cobblestones along with other organic matter, such as pollen and spores. As time went on, the acidic water trapped in the rocks dissolved the cobblestones. All that was left was the impression on the stone they once made.
“The preservation of these ghost nano-fossils is truly remarkable,” study co-author Paul Bown, a professor of micro-paleontology at University College London, said in a statement.
“Ghost fossils are extremely small – they are about five millimeters long, 15 times narrower than the width of a human hair! “But the detail of the original slabs is still perfectly visible, pressed against the surfaces of the ancient organic matter, even though the slabs themselves have disintegrated,” Bown said.
Filling a gap
Previous research has shown a decline in these fossils during previous global warming events that affected the oceans, leading scientists to believe that plankton was adversely affected by ocean acidification and climate change as a whole.
Ghost fossils tell a completely different story, providing a record showing that cobblestones were abundant in the ocean during three ocean warming events 94 million, 120 million and 183 million years ago, throughout the Jurassic and Cretaceous periods.
“Normally, paleontologists only look for fossils themselves and if they do not find them, they often assume that these ancient plankton communities have collapsed,” said study co-author Vivi Vajda, a professor at the Swedish Museum of Natural History. .
“These ghost fossils show us that sometimes the fossil record makes fun of us and that there are other ways in which this limestone nanoplankton can be preserved that must be taken into account when trying to understand the reactions to past climate change.”
Researchers first focused on the Toarcian Oceanic Anoxic Event, when volcanoes released increased carbon dioxide into the southern hemisphere and caused rapid global warming 183 million years ago during the Early Jurassic period.
Scientists have discovered ghost fossils in the United Kingdom, Japan, Germany and New Zealand associated with the event, as well as specimens found in Sweden and Italy linked to ocean warming events 120 million years ago and 94 million years, respectively.
Understanding these ghost fossils can help researchers look for them in other fossil gaps and better understand the warming periods throughout Earth’s history.
Plankton were not only resistant to rising temperatures – they actually diversified and thrived, and this may not have been good for other species.
Large plankton flowers are not a sign that an ecosystem is in trouble, but when a bloom dies and sinks to the bottom of the sea, its decomposition uses oxygen and depletes it of water, which can create areas where most species can not. to survive.
“Instead of being victims of these previous warming events, our records show that plankton multiplication contributed to the expansion of marine dead zones – areas where seabed oxygen levels were too low for most species to survive,” he said. Slater.
“These conditions, with the expansion of dead zones and the flowering of plankton, may become more prevalent in our warming global oceans,” he added.
Current global warming is happening faster than these historical events, and Slater believes this study shows that scientists need a more subtle approach to predicting how different species will react as the global climate shifts, because they will not respond. all in the same way.