Darwin visits the Blue Mountains

I live about 900 metres above sea level. Beneath me are layers of sandstone, coal, and shale built up over hundreds of millions of years of erosion, sedimentation, and compression. About 150 million years ago an enormous slab of this was forced upwards by tectonic forces, and this was followed by a period of volcanic activity caused by the movement, with volcanoes pouring a layer of basalt over the top. Weather, water, and gravity then conspired to create great cavities in the rock formation – the valleys we see today. The locality might be called the Blue Mountains, but really it's a huge plateau with very big holes in it. And it's not blue – the predominant colours are the yellows and oranges of the sandstone and the dark grey-green of gum trees. The name comes from  what Darwin called "a thin blue haze", caused by vapour emitted by the billions of eucalyptus trees.

In January 1836 Charles Darwin visited the town where I live. He stayed at the Weatherboard Hotel which was on a site now occupied by a commuter car park at Wentworth Falls railway station, and on January 17th he took a walk through the bush to the top of Wentworth Falls and looked out over the Jamison Valley. You can take the same journey today along the Charles Darwin Walk, which starts in a park and follows the path that Darwin used. (It passes a few hundred metres from my house.)

He thought he might be looking at a drained seabed, and made this comment in his diary: "If we imagine that a winding harbor with its deep water surrounded by bold cliff shores was laid dry, & that a forest sprung up on the sandy bottom, we should then have the appearance & structure which is here exhibited". He expanded the idea the next day after visiting the valleys near Blackheath. He was wrong. It had never been a sea with harbours and bays (although it had been underwater a very long time ago).  What Darwin didn't know, and which would not be known for about another century, was how old the Earth is and what the mechanism is that can push rocks upwards from under the sea. We now know about radioactivity heating the centre of the planet and the movement of tectonic plates, but there is no shame in not knowing what isn't known. Science is always a work in progress and I'm sure that there will be discoveries in the next hundred years which will show that some of our assumptions today are wrong.

Darwin was wrong about something, but what he is remembered for is the idea of natural selection driving evolution.

It is often thought that Darwin came up with the idea while on the Galapagos Islands, but in fact he didn't comprehensively study the differences in finch beaks until he was back in London. He did, however, have an epiphany long before that.

After his walk to look at the valley at the end of a "tiny rill of water", Darwin continued westwards. One of the places he visited was Newnes. This was the site of oil shale mining during World War 2, but this was abandoned as uneconomic after the war and now just consists of a pub and a camping ground. Its remaining claim to fame is an abandoned railway tunnel which has become an evolutionary niche for glow worms, and getting to that is almost as big an adventure as standing in the dark looking at the shining insects.

On the wall of a hallway in the (sadly now beer-free) Newnes Hotel there is a quotation from Darwin's diary, dated January 19, 1836. He had been observing the actions of an antlion and had noticed that the Australian variety constructed traps in the same way as ones living on other continents, although the ants were unrelated species. The diary entry says:

I had been lying on a sunny bank & was reflecting on the strange character of the animals of this country compared to the rest of the World. An unbeliever in everything beyond his own reason might exclaim, "Surely two distinct Creators must have been at work; their object is the same & certainly the end in each case is complete"  Would any two workmen ever hit on so beautiful, so simple, & yet so artificial a contrivance? It cannot be thought so. The one hand has surely worked throughout the universe.

Remember that Darwin believed in a Creator, but what he is saying here is the deist position – there might have been a creation, but since then "from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved".

And he was right about that.

This article was published as the Naked Skeptic column in the July/August 2014 edition of Australasian Science