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460 million years ago, the plates have been moving, again.
4億6000萬年前板塊再度移動，
A new continent now exists, Gondwana.
底下有一塊新大陸叫岡瓦那。
It's 90 degrees and oxygen levels are close to what they are today.
溫度約32攝氏度，氧氣濃度與現在的大氣相仿，
The land should be covered with plants and crawling with creatures.
陸地應該滿是動植物，
But there's not much here,
然而除了幾塊藻，
besides a few patches of algae.
這里什么也沒有。
There's only one explanation, the Sun.
只有一種解釋，就是太陽。
It blasts the surface with deadly radiation,
它用致命輻射照射地面，
so the complex life in the ocean doesn't stand a chance on land.
我們在海里看到的復雜生命，無法在陸地上存活。
But 30 miles up, where the rays enter the Earth's atmosphere, something is happening.
不過往上約50公里，也就是陽光進入地球大氣之處，卻出現奇怪的現象，
When oxygen meets the sun's radiation,
碰到陽光輻射之后，
it turns into another kind of gas, called ozone.
氧變成名為臭氧的氣體。
This gas forms a blanket around the planet and absorbs the lethal radiation.
這種氣體入毯子般包住地球，臭氧層吸收致命輻射。
