Reading Rocks - The Secret Of Joggins (Part 1 of 2)
The start of a two-parter uncovering the 300-million year old secret hidden in the cliffs of Joggins. It’s an unassuming spot along the shore of the Cumberland basin but it would prove to be a scientific goldmine. In part one, we see how the cliffs at Joggins helped Charles Darwin rest easy by solving a longstanding mystery about the origins of coal.
EPISODE NOTES
Joggins was a big part of my childhood. Growing up, one of the most reliable weekend day-trips for my family was to head up there early in the morning and spend the whole day sitting on the beach poring through the rocks looking for fossils. Back when we went, it did not have the beautiful visitors’ centre it does today. It was very nice to return and see the investment being made in such an important landmark.
TRANSCRIPT
On the south shore of the Cumberland Basin in Nova Scotia, you can find a totally unassuming spot that happens to be world famous.
A stretch of shoreline where jagged cliffs jut up with odd, diagonal stratification. And year after year, as coastal winds, winter frost and the Bay of Fundy’s massive tides scour them back, they reveal their 300 million year old secret.
Originally ‘Chegoggins’, a Mi’kmaq name meaning ‘place of the large fish weir’, it’s been anglicized to ‘Joggins’.
Joggins’ secret begins with the black coal seams that drew early colonists here. Samuel de Champlain uses this coal in his forges at Port Royal as early as 1603. Coal mines have been springing up at Joggins ever since. This headland is, in fact, called Coal Mine Point.
Coal-rich rock is obviously not unique to Joggins. But it’s a sign for geologists to take interest in the area. After a few preliminary surveys, the one that really puts it on the map is in 1851 by the Canadian William Dawson and the Scottish Charles Lyell.
And these two are a big deal. Dawson is credited as being the ‘first Canadian scientist of international renown’. Charles Lyell, meanwhile, wrote the incredibly influential Principles of Geology and is close friends with one Charles Darwin. And Joggins is going to change both their lives.
Because Charles Darwin… has got a real problem with coal.
Specifically: where did it come from? Darwin is convinced it has a submarine origin and is looking for evidence to that effect. Meanwhile, his friend Lyell says it has a terrestrial origin.
How crazy did this make Darwin? To quote him: “I shall never rest easy in Down church-yard without the problem to be solved by someone before I die.”
And Joggins is ground zero for their debate. Submarine or terrestrial - who’s right? The answer is hidden in these cliffs.
But to understand it, we need to understand why the origins of coal are so contentious in the first place.
Because in a lot of ways… coal doesn’t make sense.
Let’s start with what we do know. Coal is the result of a dizzyingly lengthy process even in geologic time.
Step 1: a lot of plant matter has to die. And that plant matter has to come to rest in a very specific environment that keeps it from decomposing, due to acidity and lack of oxygen. Bogs and marshes are great for this.
Step 2: Eventually, plant matter in that very specific environment will compact into peat. This already kinda takes forever. Peat forms at a rate of about 1mm per year, maxing out at about 2-3mm per year in the tropics.
Step 3: all that peat then needs to get buried under sediment layers from a flood, change in sea level or volcanic eruption.
Step 4: the weight of those sediments needs to be sufficient to squeeze the water out of the peat and compress it. So, the peat formed at about a millimetre per year and then this process compresses it 10:1.
Step 5: Once this compressed peat has been pushed 3-4 kilometres down it is subjected to enough heat and pressure to trigger chemical reactions that finally produce: coal.
This all takes millions of years - maybe hundreds of millions. Coal takes longer to form than any other rock type.
So yeah, it’s a bit of a miracle that we have any coal at all. But there’s something even weirder going on.
90% of all the coal on earth comes from one period in history: about 360 to 300 million years ago, appropriately called the ‘carboniferous’ or ‘coal age’.
So… why? What is it about this one period that produced so much coal? Not a straightforward question. One that drives Darwin crazy and leads him to his ‘submarine’ or ‘drift’ theory, which said that these masses of plant matter would have had to be transported into a marine environment. In his mind that’s the only way so much of it could collect for so long without decomposing.
Now, with the benefit of more than a hundred years of scientific progress on poor Darwin, we think we have a much better handle on all this.
The leading theory is, there’s no one wild out-of-left-field factor that clicks everything into place. The carboniferous just happened to have absolutely amazing conditions for coal production.
It’s a time of sprawling equatorial wetlands. The boggy kind perfect for producing peat. And what’s more, these enormous basins are undergoing subsidence, a geological process of constant ground-sinking which captures and buries plant matter before it has a chance to decompose.
Subsidence is rare. But one time it does happen is during continental collision when the rise of a mountain chain also creates a ‘foreland basin’. In the carbonfierous, the supercontinent Pangea is forming near the equator - simultaneously giving us tons of these tropical wetlands and subsidence basins. A perfect recipe for enormous quantities of coal like we see at Joggins.
Darwin, of course, doesn’t know any of this - they’re still grappling with the basics of where coal originated: again, he says under water. Lyell says on land.
But here, at least, Joggins can provide them with an answer.
Because in amongst the coal seams in the cliffs are some pretty startling fossils: upright tree stumps, incredibly well preserved where they grew, some with their root systems still intact.
And it’s these upright, in-situ trees among the seams of coal that help provide the evidence. They were clearly growing here. Which means: coal must have a terrestrial, not submarine, origin. Problem solved.
Darwin can rest easy in Down church-yard. But we are just getting started. Because those same fossilized trees are hiding another secret. One that will be instrumental in Darwin’s better known theory - that whole evolution thing, puts a final stamp on the coal theory and makes Joggins one of the most important fossil sites in the entire world. And that is what we’ll be finding out next time.