60秒科学:Why Didn't Earth Freeze Completely?

Why Didn't Earth Freeze Completely?
Research published in the July 2 issue of Nature reveals one reason our planet didn't succumb¹ to an enveloping² ice sheet during glacial ages. Christie Nicholson reports.

 [The following is an exact transcript³ of this podcast.]

During the last ice age our problem was too little carbon. Unlike today where too much carbon is causing global warming.

Past glacial ages occurred partly because the weathering of rocks, over millions of years, pulls CO2 from the atmosphere, locking it in ocean floor sediment⁴. The rise of global mountain ranges during the last 25 million years should have sucked all the CO2, sending the Earth to an icy death.

But that never happened. CO2 levels stabilized⁵ at about 250 parts per million.

This week in the journal Nature, researchers announce one reason why this happened: plants.

Leafy greens need CO2 to live, and when CO2 levels drop significantly they starve. Researchers say that the plant numbers decreased to a level where volcanoes and other carbon-creating sources produced CO2 faster than the remaining plants could remove it. So the Earth remained somewhat warm.

It may seem that our leafy friends could help us now, this time from overheating. But ultimately we’re producing too much CO2 too fast for natural weathering processes to remove it. Ultimately, we need a way to stop producing CO2 in the first place.

—Christie Nicholson

1 succumb   

v.屈服，屈从；死

参考例句：

• They will never succumb to the enemies.他们决不向敌人屈服。
• Will business leaders succumb to these ideas?商业领袖们会被这些观点折服吗？

2 enveloping   

v.包围，笼罩，包住( envelop的现在分词 )

参考例句：

• Always the eyes watching you and the voice enveloping you. 那眼睛总是死死盯着你，那声音总是紧紧围着你。 来自英汉文学
• The only barrier was a mosquito net, enveloping the entire bed. 唯一的障碍是那顶蚊帐罩住整个床。 来自辞典例句

3 transcript   

n.抄本，誊本，副本，肄业证书

参考例句：

• A transcript of the tapes was presented as evidence in court.一份录音带的文字本作为证据被呈交法庭。
• They wouldn't let me have a transcript of the interview.他们拒绝给我一份采访的文字整理稿。

4 sediment   

n.沉淀，沉渣，沉积(物)

参考例句：

• The sediment settled and the water was clear.杂质沉淀后，水变清了。
• Sediment begins to choke the channel's opening.沉积物开始淤塞河道口。

5 stabilized   

v.（使）稳定， （使）稳固( stabilize的过去式和过去分词 )

参考例句：

• The patient's condition stabilized. 患者的病情稳定下来。
• His blood pressure has stabilized. 他的血压已经稳定下来了。 来自《现代英汉综合大词典》