Springing to Extinction in Spring春季中的寂灭

Imagine a warm spring day about 66 million years ago. Fish would have been swimming in the rivers in an area that’s now North Dakota in the US. Seconds later， the serenity was ended by destruction.

These could have been the very last moments of the dinosaur era when a city-sized asteroid struck Earth， killing off three quarters of all species on the planet. According to a study published in Nature on Feb 23， 2022 the asteroid hit in springtime.

Scientists have long been confused over the time of year the asteroid hit， and how some animals managed to survive while dinosaurs didn’t.

Researchers in 2019 discovered fossilized fishes in North Dakota that died shortly after the asteroid hit Earth. They examined the fossils with a particle accelerator and found out there was seasonal growth on the bones. All fish bone cell densities and volumes can indicate the season.

想象一下大约6 600万年前一个温暖的春天，在位于现今美国北达科他州区域的河流中，鱼儿畅游着，几秒钟后，毁灭终结了这份宁静。

这也许是恐龙时代的最后时刻，因为一颗城市大小的小行星撞击地球，杀死了地球上四分之三的物种。根据2022年2月23日《自然》杂志上发表的一项研究，小行星撞击地球是在春季。

长期以来，科学家们一直对小行星撞击地球的时间困惑不清，也不清楚为何一些动物能存活下来，而恐龙却未能活命。

2019年，研究人员在北达科他州发现了鱼类化石，这些鱼类在小行星撞击地球后不久死亡。研究人员用粒子加速器检查了化石，发现鱼骨上显示出季节性生长。所有的鱼骨细胞密度和体积都可以表明季节。

The timing of the collision， at least for the Northern Hemisphere， came at a particularly sensitive stage. “I think spring puts a large group of the late Cretaceous biota in a very vulnerable spot because they were out and about looking for food， tending to offspring and trying to build up resources after the harsh winter，” Melanie During， the main author of the study， said at a news briefing.

In the Southern Hemisphere， it was autumn， a season when many creatures prepare for winter. Therefore， life in the Southern Hemisphere was a lot more prepared for this event.

It is unclear whether small animals in the Northern Hemisphere actually did worse than those in the south. There is evidence that Northern Hemisphere turtles were wiped out in the asteroid strike， after which their habitats were later repopulated by turtles from the south， Dennis Voeten， a researcher at Uppsala University in Sweden told The Guardian.

Nothing much larger than a house cat survived the asteroid impact and many species would have been doomed whenever it hit， Daniel Field， an assistant professor at the University of Cambridge in the UK， told The Guardian.

小行星撞击地球的时间，至少对于北半球来说，是一个特别敏感的阶段。这项研究的第一作者梅勒妮·杜林在一次新闻发布会上说：“我认为春天令一大群白垩纪晚期生物处在了一个非常脆弱的境地，因为它们忙着外出寻找食物，照顾后代，以及在严冬后累积物资。”

南半球正值秋天，这是许多生物准备过冬的季节。因此，南半球的生物对这一事件有了更充分的准备。

目前尚不清楚北半球的生物是否真的比南半球的生物表现得更糟。瑞典乌普拉大学研究员丹尼斯·沃滕在接受英国《卫报》采访时表示，有证据表明，北半球的海龟在小行星撞击地球时灭绝了，之后它们的栖息地被来自南半球的海龟所占据。

英国剑桥大学助理教授丹尼尔·菲尔德在接受《卫报》采访时表示，体型比家猫大的动物没能在小行星撞击地球时幸存下来，无论何时，撞击一旦发生，许多物种就难逃厄运。

Word Bank

serenity /sə'renəti/ n. 平静；宁静

fossilized /'fɒsəlaɪzd/ adj. 石化的

sensitive /'sensətɪv/ adj. 敏感的

My teeth are very sensitive to cold food.

offspring /'ɒfsprɪŋ/ n. 后代；（动物的）幼崽

evidence /'evɪdəns/ n. 證据；证明