When Did Whales Get So Large?
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Three million years may seem like a long time. But when you consider that planet Earth is more than 4.5 billion years old, it is a pretty short period of time.
And it is over that shorter time period that the whales in our oceans today got to be so large.
The blue whale is the largest animal that has ever lived. They weigh more than even the biggest dinosaurs. They can grow to 30 meters long and weigh up to 130,000 kilograms.
Blue whales are part of the baleen whale family. Baleen is a kind of food-filtering structure in the mouths of the whales. The whales developed this system about 30 million years ago.
Other whales in the baleen family include fin whales, bowhead whales, and right whales. Today, these whales can weigh well over 70,000 kilograms.
But for millions of years, they were not nearly that large, scientists say.
"All of a sudden – ‘boom' – we see them get very big, like blue whales," scientist Nick Pyenson told the New York Times. He and other researchers recently published an article on whale size in the British research journal Proceedings of the Royal Society B.
"It's like going from whales the size of minivans to longer than two school buses," Pyenson added.
The researchers -- Pyenson, Jeremy Goldbogen and Graham Slater -- believe that a change in the Earth's climate caused whales to get so large only about 3 million years ago.
This change led to food becoming more easily available.
An oncoming ice age made the ocean water cold. High winds mixed the water in the ocean faster than before. Rain and snow made more nutrients run off from the land into the water. The nutrients resulted in algae. That attracted small fish and shrimp called krill.
The mixture of nutrients resulted in more food for large whales to eat.
Whales that were able to quickly eat a lot of food survived. And they got larger. Whales that had teeth instead of baleen, however, did not survive.
The largest baleen whales then produced other large whales.
Over the next three or four million years, the baleen whales grew 10 times bigger than they had been, the researchers say.
It is possible that the largest whales are gone, the researchers said. But, as they told the BBC, blue whales could grow even bigger -- or they could slowly die – depending on Earth's changing climate.
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1.depending on 根据；取决于
I tend to have a different answer, depending on the family.
2.instead of 代替
Instead of snacking on crisps and chocolate, nibble on celery or carrot.
3.run off 逃跑
The last thing I'm going to do is run off with some-body's husband.
4.High winds 狂风
High winds have knocked down trees and power lines.
1.But when you consider that planet Earth is more than 4.5 billion years old, it is a pretty short period of time.
a short period of time 短时间；短期内
I have never seen such a seismic shift in public opinion in such a short period of time.
How could you do it in such a short period of time?
2.The mixture of nutrients resulted in more food for large whales to eat.
resulted in 导致
The speech has resulted in a firestorm of controversy.
The boom in building has resulted in the local land being more valuable now for houses.
蓝鲸是有史以来体型最大的动物，它们的体重甚至超过最大的恐龙 。蓝鲸身长可达30米，体重可达130吨 。
蓝鲸属于须鲸 。鲸须可以过滤鲸鱼口腔内的食物 。3000万年前，鲸鱼进化出这一过滤系统 。
其它须鲸类鲸鱼还包括长须鲸、弓头鲸和露脊鲸 。现如今，这些鲸鱼的体重远超过70吨 。
科学家尼克·派森（Nick Pyenson）对《纽约时报》表示，“突然之间，它们的体型像蓝鲸一样发生了巨变 。”近日，派森和其它研究人员在《英国皇家学会会刊B辑》上发表了一篇关于鲸鱼体型变化的研究 。
研究员派森、杰里米·葛保根（ Goldbogen）和格雷厄姆·斯莱特（Graham Slater）指出，大约300万年前，地球的气候变化导致鲸鱼体型发生巨变 。
即将来临的冰河时代导致海水温度骤降 。狂风使海水流动得更快 。雨雪夹带着陆地上的营养物质流入大海 。这种养分滋生了藻类，进而吸引了鱼虾 。
那些快速补充大量食物的鲸鱼得以存活，它们的体型也愈加庞大 。而那些有牙齿但没有鲸须的鲸鱼被环境淘汰 。
研究人员表示，这种最大的鲸鱼有可能消失 。不过正如他们对英国广播公司所说，蓝鲸是继续进化还是逐渐灭绝皆取决于地球的气候变化 。