What do core samples tell us?

Dr Demian Saffer and Aliki Weststrate from JOIDES Resolution expedition #375 tell us how scientists read the clues found in core samples taken from deep under the ocean.

Point of interest: Why do you think Aliki compares magnetic reversals to a barcode in the rock?

Note: This video footage was bounced off a satellite during a Skype session with Otumoetai Intermediate School students. If you find the sound quality difficult, please refer to the transcript.

Transcript

DR DEMIAN SAFFER

If we look at the cores, they don’t tell us anything about the time of an earthquake, but what they do tell us about is the time during which they were laid down, so when these sediments were approximately deposited. There are a couple of different ways to tell how old they are, and as they are laid down, of course, they are laid down in layers. The oldest ones are on the bottom and then they get younger as you go up. And the two primary ways that we figure out how long that takes or how old the rocks are with fossils or with the magnetic signatures.

The fossils – we use the word microfossils – and if you look under a microscope, you see these tiny shells. We know that certain collections of species were around in certain time periods in Earth’s history, and that’s really well calibrated or really well known and so you can actually start to map out say the bottom of this core might be 30 million years old and a few metres above that it might be 28 million years old, so you not only get the ages but you also figure out then whether there are time periods where things were laid down really rapidly, time built up quickly or time periods where maybe it was more slowly deposited.

And the other way that we can view this is taking detailed magnetic measurements, and that is again a way of measuring time because we also know that Earth’s magnetic fields flip back and forth over its history and that’s known kind of independently, it’s known pretty well. So mapping those what are known as magnetic reversals down the core is basically like going back in time when you go down the core, so you can figure out the ages of the material based on those flip flops of the magnetic field that are preserved in the rock.

ALIKI WESTSTRATE

And you can hear that beeping behind us, that’s virtually what Demian is talking about. That’s from the cryomagnetometer, which is measuring the magnetic reversals. It’s like a barcode in the rock.

Acknowledgements Dr Demian Saffer, Pennsylvania State University Aliki Weststrate International Ocean Discovery Program (IODP) Australia and New Zealand International Ocean Discovery Program Consortium (ANZIC) GNS Science Otumoetai Intermediate School Close-up footage of dinoflagellates micrographs and microscope from JOIDES Resolution expedition #318 by ZCENE Moving Media for IODP courtesy of Ocean Leadership, IODP and ZCENE Three stills of cryomagnetometer courtesy of Nina Rooks Cast, IODP and JOIDES Resolution Science Operator All other footage from ship to shore video conference from JOIDES Resolution expedition #375 courtesy of Otumoetai Intermediate School