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Current Events: 7 billion-year-old stardust is the oldest stuff on Earth

By Stacy Palen

I recently stumbled upon this article from The Washington Post about stardust on Earth. Mineral dust in the Murchison meteorite shows traces of neon produced by cosmic rays as the dust traveled through space. The abundance of neon atoms indicates that the dust was formed 7 billion years ago—before the Sun formed.

Here are some questions to ask your students based on the article:

1) What produces neon atoms in grains of interstellar dust?

Answer: Cosmic rays smash into the grain and convert silicon into neon.

 

2) How does the rate of cosmic rays striking the dust change with time?

Answer: It doesn’t. This rate is constant.

 

3) Suppose that one grain of dust has twice as much neon as another grain. What can you conclude about the relative time each grain spent in space?

Answer: The one with twice as much neon was out there twice as long.

 

4) In your own words, describe how astronomers determine the age of a grain of interstellar dust.

Answer: Astronomers count the number of neon atoms and compare that number to the number of neon atoms in a grain of known age. If there are more neon atoms, the dust grain was roaming the galaxy longer.

 

5) How old is the Sun, and how do we know?

Answer: The Sun is about 4.5 billion years old. We know this from measuring isotope abundances in moon rocks.

 

6) Are these dust grains older or younger than the Solar System?

Answer: These dust grains are 2.5 billion years older than the Solar System.

 

7) Is this result consistent with the idea that stars recycle material from the interstellar medium when they form? Explain.

Answer: Yes! Because the Sun and planets formed from material lost from earlier stars (we know this because of the abundance of other materials. Some of that material is still floating in the Solar System, and some of it was lost from stars that died long before the Solar System formed.

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