Earth’s Climate Swings

For years some scientists have hypothesized about the existence of the earth’s natural climate cycles. Now, some researchers believe there is physical evidence to support this. Dennis Kent, an expert in paleomagnetism, the study of magnetic fields in rocks, has co-authored a study that analyzes rocks to show how the earth’s climate is dictated by cycles. He joins Hari Sreenivasan to discuss.


For years, some scientists have hypothesized about the existence of the Earth's natural climate cycles.

Now some researchers believe there is physical evidence to support this.

Dennis Kent, an expert in paleomagnetism, the study of magnetic fields in rocks, has coauthored a study that analyzes rocks to show how the Earth's climate is dictated by cycles.

He's here today to talk about his study, so tell me.

What'd you find?

Well, the springboard is actually just across the river from where we're speaking in New Jersey, where, 200 million years ago, way back in geologic time, was a series of lake beds and accumulated literally many miles of sediment, and in the course of this, there's a rhythmicity that's been obvious there now, been documented in more and more detail, and this rhythmicity, or cyclicity, can be discerned actually very simply by the colors of the rock often so that the rocks that are dark colored are those that surmised to be deposited under deep water, where there's very little oxygen so that the carbon content sort of colored the rock, and then other times when the lakes literally dried out, the sediments became red, and so they had essentially ancient soils.

And so this is the alternation in interpreting climate, essentially precipitation in this case, and many, many of these cycles been recorded, but one of the difficulties was that there's very little to date in the sediments themselves, ways of independently determining what the periodicity, or the timing, between these rhythms are.

So, when you are talking about these lake beds, I'm just imaging in my head here.

If I could kind of push the lake bed back, you'd have a giant cross section, and you'd be digging straight down, kind of like ice-core samples, and you could say, 'Oh, a rock from here versus a rock from there versus a rock from here,' right?

Is that what you...

That's right, yeah.

It's almost like a cake, a layer cake.

That's exactly right, and these are ancient, so they've... The lakes are long gone.

There's been tectonic, or the land has been uplifted, incised, but to make it convenient, we've taken cores through these thousands of feet of core that record these in a very accurate and precise way.

So, if you see this, you're able to tell what, that there were periods of incredible rain and dry spells or...

That's pretty much.

It's how rainy it is when that's the times when the lake fills up and then times when it rains less or is when the drier conditions, the lake literally dries out, quite analogous to actually the East African lake systems.

Many of those have gone in a more recent geologic past through these cycles of drying out and then being full.

So you're talking about time scales that are hard for us to wrap our heads around, hundreds of millions of years.

This is well before humans ever walked the Earth, right?

Well before.

Right, so what else can you start to extrapolate from this?

In this case, we're looking.

The rhythmicity is essentially a signal.

We're looking from a relation to the rest of the solar system.

It's our clock.

It's the periodic motions of the planets going around the sun, and they're influencing Earth's orbit and the way we receive sun over the course of a year and then over the eons, and it's this rhythmicity that's the back-and-forth that we've been particularly interested in because that's a potential clock, and we want to then be able to calibrate that clock, so then when we see it in other places, we'll be able to utilize it so to document what the course of climate change or whatever else might be recorded in these particular sediments or particular time.

I'm sure that yourself and other researchers have been conscious of the climate science and the climate-science denial that's been happening.

What if someone looks at your work and says, 'You know what?

Here is proof that humans aren't causing climate change because look at these cycles that he's proving in the rock.'

Well, I don't think there's any much doubt that there's been climate change in the past, and since it's before humans, then it's natural, if you will.


And these have been very large, so, for example, of most recently is the change from a glacial interval, where we're sitting now in Manhattan had quite a bit of ice here that withdrew some 10,000 years ago.

So, there have been very large climate changes, but that's not to say that we don't have an influence on going forward.

All right.

Dennis Kent from Columbia University Lamont-Doherty Earth Observatory, thanks so much for joining us.

You're quite welcome.