72: Classification and Dating of Meteorites 3. Cosmochemist Greg Brennecka details meteorite classifications, emphasizing chondrites—primitive, unmelted samples representing the early molecular cloud and serving as the "baby book" of the solar system—whereas
The John Batchelor Show
John Batchelor
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🗓️ 10 November 2025
⏱️ 13 minutes
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Summary
3. Cosmochemist Greg Brennecka details meteorite classifications, emphasizing chondrites—primitive, unmelted samples representing the early molecular cloud and serving as the "baby book" of the solar system—whereas acondrites have been melted and often come from differentiated or disrupted planets. Brennecka specializes in Calcium Aluminum-rich Inclusions (CAIs) found within chondrites, which are used as a precise clock to date the solar system at 4.567 billion years old, and another stunning type is the pallasite, believed to originate from the core-mantle boundary of a planet and featuring spectacular olivine crystals in an iron matrix. Modern cosmochemistry relies on techniques like solution chemistry, where samples are dissolved in acid to precisely measure isotopes and elements.
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| 0:30.7 | This is CBSI in the world. |
| 0:32.4 | I'm John Batchel. |
| 0:33.4 | Impact is the book. |
| 0:34.9 | This is meteorites that fall to earth and what we've learned about our solar system, about |
| 0:40.0 | life, about water, about our understanding of where we come from. |
| 0:45.9 | Impact is the book, how rocks from space led to life, culture, and Donkey Kong. |
| 0:49.9 | Greg Branaka, a cosmochemist here. |
| 0:52.7 | And Greg, you teach me there are three kinds of meteorites that fall to Earth, our classifications. What are they? And you study one particular kind of meteorite, I believe, the CAIs. What is that? First, the three kinds. Thank you. |
| 1:09.0 | Okay. Well, I guess I'll have to slightly correct you. There's a lot more than three kinds. I think there's three main kinds of chondrites. So I'll just, you know, kind of break it up into that. There are chondrites, which are really primitive samples, and then there are achondrites, which have melted. There are three types of chondrites. |
| 1:32.9 | And one of those, you mentioned the CAIs or calcium aluminum-rich inclusions, |
| 1:37.4 | and you can see why we abbreviate it, that's something that's contained in these carbonaceous chondrites. |
| 1:40.2 | And they're kind of the earliest snapshots of our solar system, so as it was just starting to form. |
| 1:45.2 | So the chondrites are important because they are a journey back to the four billion years ago |
| 1:51.5 | when the cloud was gathering itself around what becomes the sun. |
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