臭氧层破坏可导致生物大灭绝
We used to think that it would take something as 1. ____________(power) as an asteroid (小行星) impact or large-scale volcanic eruptions to wipe out life on Earth. In fact, these two forces did lead to four of the five “mass extinctions” in Earth’s history, including the one 2. ______killed the dinosaurs 66 million years ago. But the cause of the Late Devonian extinction, which happened 360 million years ago, remained a mystery – until now. The cause turned out to be neither asteroids(小行星)4. ______volcanoes, but something much 3. __________(close) to home – a broken ozone layer (臭氧层).
Researchers from the University of Southampton, UK, collected ancient rock samples from both polar regions and places along the equator (赤道), and extracted (提取) fossilized (石化的) plant spores (孢子) from the rocks.
In the study, John Marshall, a paleontologist (古生物学家) at the University of Southampton, wrote: “All of the ozone protection was gone.”
Researchers believed that it was only a “brief breakdown” that 5. _________(occur) immediately after an ice age. The melting ice sheets 6. __________(quick) released a large amount of heat into the air, pushing more naturally generated ozone-destroying chemicals into the atmosphere.
But no matter 7. ________brief it was, the temporary absence of the ozone layer – which normally shields (防护) Earth from the damaging UV radiation – still killed much of the Earth’s plants and freshwater animals back then.
“A similar collapse (崩溃) of the ozone layer could occur again, exposing surface and shallow sea life 8. ______deadly radiation,” Marshall told Science Daily. “This would move us from the current state of climate change to a climate emergency.”
It’s time that we 9. ________(start) taking the protection of the ozone layer 10. ____________(serious) , so that Earth doesn’t experience its sixth mass extinction – one that we humans may not escape from.
1. powerful 2. that 3. nor 4. closer 5. occurred 6. quickly 7. how 8. to 9. started 10. seriously
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