3. The end of life on Earth?

Part 3

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提醒：於閱讀中您可以使用下表中的學習資源查詢您於閱讀中所想多了解的字彙或是您認為對閱讀該段落重要的單字。

The Earth has been kept fairly safe for the last 65 million years by good fortune and the massive gravitational field of the planet Jupiter. Our cosmic guardian, with its stable circular orbit far from the sun, sweeps up and scatters away most of the dangerous comets and asteroids which might cross Earth’s orbit. After the Chelyabinsk meteorite, scientists are now monitoring potential hazards even more carefully but, as far as they know, there is no danger in the foreseeable future.

Types of space rocks

• Comet – a ball of rock and ice that sends out a tail of gas and dust behind it. Bright comets only appear in our visible night sky about once every ten years.
• Asteroid – a rock a few feet to several kms in diameter. Unlike comets, asteroids have no tail. Most are too small to cause any damage and burn up in the atmosphere. They appear to us as ‘shooting stars’.
• Meteoroid – part of an asteroid or comet.
• Meteorite – what a meteoroid is called when it hits Earth.

學習資源：

No.	Learning Resources	Link
1.	Cambridge Dictionary	https://dictionary.cambridge.org/
2.	String Net	http://nav.stringnet.org/
3.	Longman English Dictionary Online	https://www.ldoceonline.com/
4.	Wiktionary	https://www.wiktionary.org/
5.	Collins Dictionary	https://www.collinsdictionary.com/

恭喜你完成了第三部分的閱讀！！

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謝謝您這次的研究參與！