July 2, 2018
University of Exeter
The evolution of Earth's first
animals more than 500 million years ago caused global warming, new research
shows.
The evolution of Earth's first
animals more than 500 million years ago caused global warming, new research
shows.
Some 520-540 million years ago,
animal life evolved in the ocean and began breaking down organic material on
the seafloor, leading to more carbon dioxide and less oxygen in the atmosphere.
In the 100 million years that
followed, conditions for these earliest animals became much harsher, as ocean
oxygen levels fell and carbon dioxide caused global warming.
The research, published
in Nature Communications, is from the Universities of Exeter, Leeds and
Antwerp, and the Vrije Universiteit Brussel.
"Like worms in a garden,
tiny creatures on the seabed disturb, mix and recycle dead organic material --
a process known as bioturbation," said Professor Tim Lenton, from the
University of Exeter.
"Because the effect of
animals burrowing is so big, you would expect to see big changes in the
environment when the whole ocean floor changes from an undisturbed state to a
bioturbated state."
"We did indeed see a
decrease in oxygen levels in the ocean around 520 million years ago," said
Professor Filip Meysman, from the University of Antwerp.
"But evidence from the
rock record showed sediment was only a little disturbed."
Professor Simon Poulton, from
the University of Leeds, said: "This meant that the animals living in the
seafloor at that time were not very active, and did not move very deep into the
seabed.
"At first sight, these
two observations did not seem to add up."
Lead author Dr Sebastiaan van
de Velde, of the Vrije Universiteit Brussel, explained: "The critical
factor was to realise that the biggest changes happen at the lowest levels of
animal activity.
"This meant that the
first bioturbators had a massive impact."
The researchers said this
realisation was the "missing piece of the puzzle," and allowed them
to construct a mathematical model of Earth around that time to look to the
changes caused by these early life forms.
Dr Benjamin Mills, also from
the University of Leeds, who led this part of the research, said: "When we
ran our model, we were surprised by what we saw.
"The evolution of these
small animals did indeed decrease the oxygen in the ocean and atmosphere, but
also increased atmospheric carbon dioxide levels to such an extent that it
caused a global warming event.
"We knew that warming occurred
at this point in Earth history, but did not realise it could be driven by
animals."
This process made conditions
worse for these animals, which possibly contributed to a number of mass
extinction events during the first 100 million years of animal evolution.
"There is an interesting
parallel between the earliest animals changing their world in a way that was
bad for them, and what we human animals are doing to the planet now," said
Professor Lenton, director of Exeter's new Global Systems Institute, which aims
to develop transformative solutions to the challenges facing the world today.
"We are creating a hotter
world with expanding ocean anoxia (oxygen deficiency) which is bad for us and a
lot of other creatures we share the planet with."
Story Source:
Materials provided by University of Exeter. Note:
Content may be edited for style and length.
Journal Reference:
Sebastiaan van de Velde,
Benjamin J. W. Mills, Filip J. R. Meysman, Timothy M. Lenton, Simon W.
Poulton. Early Palaeozoic ocean anoxia and global warming driven by the
evolution of shallow burrowing. Nature Communications, 2018; 9 (1)
DOI: 10.1038/s41467-018-04973-4
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