Scientists say the excess heavy nitrogen could have come from a comet.

科学家认为过量的重氮来自彗星。

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Scientists say the excess heavy nitrogen could have come from a comet. And the heavier oxygen from a natural process that left more of the light isotope in the part of the nebula that made the sun.

科学家认为重氮来自一颗彗星，而重氧则是来自行星形成的自然过程，这一过程把更轻的氧同位素留在了星云中，形成了太阳。

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In areas with heavy automobile traffic, however, the seed germinates in the absence of fire, with automobile exhaust supplying the required nitrogen dioxide.

然而，在汽车交通繁忙的地区，种子在没有火灾的情况下借助汽车尾气提供所需的二氧化氮发芽。

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What ails Modesto is what ails Bakersfield (No. 1), Hanford (No. 3), Fresno (No. 4) and other small Central Valley cities (the Valley accounts for all the California cites on the list aside from Los Angeles): heavy doses of nitrogen oxide and hydrocarbons stemming from gasoline, chemical processing, paints and other industrial byproducts that harm the ozone and release particle pollution into the air.

FORBES: The Worst Cities In America For Your Lungs

The Anthropocene's equivalent of iridium is nitrogen - although there will be other candidates (such as heavy metals, and carbon isotope ratios characteristic of fossil fuel emissions) for geochemists of the far future to identify as the chemical signature of the new epoch's dawn.

BBC: Leaving our mark: Fossils of the future