SSS 2008-09-30

（单词翻译）

This is Scientific American's 60-Second Science. I'm Cynthia Graber. This will just take a minute.

The Earth’s crust is old. Billions of years old. So old that it’s nearly impossible to imagine. And now scientists have discovered what may be the oldest whole rocks ever known. Geologists¹ at Carnegie Mellon University published the results of the research in the September 26th issue of the journal Science.

The rocks come from an area of the Hudson Bay in northern Quebec. In 2001 the geologists identified the site as a possible repository of very old rocks. It is made up of folds of volcanic² and what are called metasedentary rocks. And it’s surrounded by three-and-a-half-billion-year-old tonalite.

Researchers collected rocks and measured minute isotopic³ variations in rare earth elements called neodymium and samarium. According to dating techniques, the rocks could be 4.28 billion years old. It’s rare to find rocks that date back to when the Earth’s mantle⁴ was forming. It was quite a tumultuous time, and most rocks were smashed up into tiny pieces again and again. Learning more about these whole rocks could help us gain a better understanding of the very beginnings of our planet.

Thanks for the minute for Scientific American's 60-Second Science. I'm Cynthia Graber.