香港六合彩

The findings, published in Science Advances, support the theory that darkness drove the global extinctions, after an asteroid impact, as plankton and plants would not have been able to use photosynthesis to get their energy from the sun.

Co-lead author Professor Paul Bown (香港六合彩 Earth Sciences) said: 鈥淲e found that before the dinosaurs went extinct, plankton were similar to modern-day plankton as they got their energy directly from the sun 鈥� but that all changed very suddenly.鈥�

鈥淎fter a massive asteroid strike, most of the plankton that persisted used a different survival strategy, by hunting and ingesting food.

鈥淥ur findings add to a growing body of evidence that the last global mass extinction was driven by a global darkness, and was probably the only truly geologically instantaneous mass extinction event.鈥�

The research team used an exceptional record of plankton fossils and eco-evolutionary modelling techniques to examine how organisms behaved before and after this event, which killed three quarters of life on earth 鈥� and why some survived and some didn鈥檛.

The team found that prior to the asteroid impact, species of nannoplankton 鈥� microscopic algae 鈥� were exclusively reliant on harnessing energy from sunlight (photoautotrophs), but those living afterwards were capable of capturing food and eating it in addition to using photosynthesis to feed (mixotrophs). This suggests the blocking of light from the sun played an important role in killing off some species and over time, encouraging others to evolve and adapt.听 听

The research team鈥檚 breakthrough came when they found that many of the nannoplankton skeletons (coccospheres) post mass-extinction included a large hole, indicating the position of flagella 鈥� tiny tail like structures used by the algae for movement and feeding. This indicates these microscopic organisms, which survived the asteroid strike, were capable of hunting and ingesting food.

Co-lead author Dr Samantha Gibbs (University of Southampton) said: 鈥淭hose species that were lost at the mass extinction show no evidence of a mixotrophic lifestyle and were likely to be completely reliant on sunlight and photosynthesis. Fossils following the Cretaceous鈥揚aleogene (K鈥揚g) extinction show that mixotrophy dominated and our model indicates this is because of the exceptional abundance of small prey cells 鈥� most likely surviving bacteria 鈥� and reduced numbers of larger 鈥榞razers鈥� in the post-extinction oceans.鈥�

Opposing evolutionary forces led to the emergence of more diverse feeding strategies and eventually a return to greater reliance on photosynthesis in open ocean nannoplankton. Most nannoplankton today only photosynthesise.

The K/Pg event was triggered by an asteroid impact that formed the Chicxulub crater in Mexico, and is well known for the extinction of dinosaurs, plesiosaurs, ammonites and many other groups.

Professor Bown said: 鈥淭his huge impact flung vast amounts of debris, aerosols and soot into the atmosphere, causing darkness, cooling and acidification over days and years.

鈥淭he significant bias found in the nannoplankton extinctions 鈥� removal of open-ocean photoautotrophs but survival of mixotrophs that could hunt and feed 鈥� can only be fully explained by the darkness caused by the asteroid impact acting as a kill mechanism.鈥�

Dr Gibbs added: 鈥淭his 鈥榖lackout鈥� or shutdown of primary productivity would have been felt across all of Earth鈥檚 ecosystems and reveals that the K/Pg event is distinct from all other mass extinctions that have shaped the history of life, both in its rapidity, related to an instantaneous impact event, and its darkness kill mechanism, which shook the foundations of the food chains.鈥�

The study was conducted by researchers at 香港六合彩 and University of Southampton alongside colleagues in Paris, California, Bristol and Edinburgh.

Links

• 香港六合彩 Earth Sciences
• 香港六合彩 Faculty of Mathematical & Physical Sciences

Source

Image

• Prehistoric plankton with flagellar openings that would have been used for feeding. (Gibbs, Bown et al 2020)

Media contact

Chris Lane

Tel: +44 (0)20 7679 9222

Email: chris.lane [at] ucl.ac.uk