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Saturday, 28 September 2019

The first signs of spring

The pedants say we should wait until the first day of September to claim a true spring, but nobody ever told that to a body of water in the mid-Pacific, called El Niño.  This warm wet blob causes profound effects in our weather, and pays no attention to seasons at all.  Instead of having seasons, Australians have the El Niño cycle of flood and drought.  But if we ever have a spring at all, it truly begins somewhere in early August, and drifts into low summer soon after.

Early August is the flowering time for many bush wildflowers, the native flowers that cover our headlands and national parks.  August 1 has always been the traditional day to go out and admire the wattle trees, so it is no surprise to find them flowering, but a minute's searching can detect a dozen other species in five different families, in the bush just behind my house.  Even the imported plants, the magnolias and the flowering peaches and cherries are in full flower, and the first clover flowers are showing up in our lawn by the start of August, to the delight of the bees. Now, in late September, as I write this, the plants are all setting their seed.

Last Sunday, I went for a walk on a local beach.  As I expected, several local teenagers were in the water, boogie-boarding in wet suits, but I was a little surprised to see two more just swimming in the ordinary way, wearing normal swimming costumes.  We breed our kids tough!!

The best indications of promise come from the television, full as it is with football finals fever.  There are four main codes of football in Australia: Rugby League and Rugby Union, soccer (just 'football' to its adherents) and ‘Aussie Rules’, a sort of Gaelic football played 18 a side with eight goal posts.  There is also a bit of Gaelic football here and there, and rather more gridiron.  Each of these codes is reaching season's end, and so the TV news each night is full of rivetting facts about this player's groin injury, that one's hamstring, and the other's suspension for dangerous play.  Once we are free of football, then summer must be here. One more week, and that will be gone.

I drive every Tuesday morning on winding roads, so I am very aware of the sun's annual movements.  No longer does it shine straight down one hill near the sanctuary that I must climb in the morning, for the morning sun was already drifting south along the horizon by August, and now it is high enough in the sky to be behind a tree as I tootle up the hill at 7.30 am.

Our sunrise varies between 7 in winter and 5 in summer, while sunset is between 5 pm and 7 pm (ignoring daylight saving, that is).  By late August, the sunrise is  a minute earlier each day, and sunset is a minute later, so clearly we are over the hump. After October 20, the pace slows down.


An image from my book, Australian Backyard Earth Scientist. This shows sunset movement, close to the solstice.



By late August, the signs of spring were all round us.  Suburban parents send their younger children out wearing plastic ice-cream containers on their heads, with two eyes drawn on the back.  Magpies are beginning to stake out their nesting territories, and children can be pecked on the head quite painfully.

But the best sign that spring is truly sprung comes when we see fifty thousand sweaty, liniment-reeking Australians, all heading from the centre of the city to Bondi Beach in the annual ‘City to Surf’ run. That happens in mid-August.

This race begins almost outside Hyde Park.  Each year in the 1990s, two hundred sensible hedonists gathered on the museum's roof top for a champagne and croissant breakfast, arranged by the Australian Museum Society, one of my favourite organisations.  As sports-loving Australians, of course, we watched the start of the race first, to build up our appetite for breakfast.  The champagne would take a punishing during this gruelling period, but we remain respectfully hungry.

I travelled to town on an early ferry one morning six weeks back with my wife, and strolled up to the museum, through streets unusually full of Lycra and Reeboks. In the past, she has been known to run in the race, though a long-lasting injury has put her out, at least for this year, but she offered me some insights about what goes on when you are on the inside of the Gallant Hundred Thousand (I may be exaggerating: it may be only 70,000).

All competitors are colour-coded, she explained, pointing to the number on a 70-year-old matron trotting past us.  She was a blue, one of the ‘runners’.  Out front, we have the super-elite, people in the top ranks for marathon and half-marathon running.  Just behind them, are the ordinary elite, people who have previously run the 12 km City to Surf in good time. Then come the rest of those entering as ‘runners’, which is where our matron would have been.  There are probably 12 or 15 thousand runners in all, and they start first, led by the elite group.

In a street to the right, there are about the same number of ‘joggers’.  In this area, you will usually find a trio in gorilla suits, four men wheeling a refrigerator, a medical group wheeling a hospital bed, Coke cans, giant grains of rice, and other novelty groups, as well as some serious parents pushing strollers and prams at the jog, and some teenagers.

These classifications are a bit rough and ready, for there are always a few break-away joggers who dash out at the second gun, and quickly begin overhauling the last of the runners, but these are a cut above the ‘walkers’.

Finally, out to the left, are the 20-25 thousand walkers, many of whom run out at the third gun to start working their way up through the joggers.  Many of these are on their first attempt, and will move into higher ranks in later years, but there are also wheelchair pushers here, more parents with prams and strollers, and kids aged from about ten up, running in their own right.  This year, there was also a large group of fat people waddling along, carrying helium balloons.  My wife thought it was to camouflage their obesity, but I think they were hoping to take some of the weight off their feet.

Fifty thousand people make a lot of noise, especially when they cheer together.  They are a good-spirited crowd, and an hour before the start, the walkers were gathered in their starting area.  Soon, four inflated balls were bouncing around over the crowd, continually pushed aloft by willing hands.  If a ball went beyond their area, a marshal would run to retrieve it, and send it back into the crowd again.

Time passed, and people started to warm up in the three seething masses.  Soon sweat shirts, jumpers, and other forms of top cover were taken off and thrown to the sides of the eight-lane roadway.  People wear old ‘discardables’, and you just throw towards the nearest side.  Those closer to the sides take anything that lands on them, and throw it further to the side.  Just before the race, you look down on a sea of faces, with items of clothing leaping in graceful parabolas over the surface, like a school of mullet pursued by a large hungry fish.  Now they are in their racing finery, numbers pinned to their chests.

At the first gun, the runners start, as the marshals who have been standing in front of them sprint to safety at the roadside.  The lesser groups cheer, and then all is silent as they head downhill.  Silent, that is, except for about 30 000 running shoes pattering on the tar surface, which sums to an almost deafening roar. Before the last runners pass the start line, the leaders have reached the valley below, climbed the other side, and headed into the Kings Cross tunnel that leads to the next downhill run.

As the last runners clear the intersection, the joggers have their start, and soon after, the walkers take off.  Ten minutes later, as the last walkers cross the start line, the sweeping machines move in to clear up.  By the time the last Irish dancing team has jigged over the start line, stopping frequently to pose for the curious cameras wielded by swarms of shutter-hungry and bemused Japanese, the first runners have climbed Heartbreak Hill, and they are through the pain barrier at the half-way point.

By the time the last walkers reach the tunnel, the sweeping machines at the start line are done, the barricades are cleared, traffic is back to normal, and the first runner is already pushing through the tape at Bondi, 12 km and 42 minutes away.  People will continue to straggle into Bondi for around three hours more, and there will probably be forty thousand finishers.

As they run, they will pass below a number of cameras mounted strategically over the road, and are photographed from a position which shows their entrant numbers.  In a few weeks, letters will arrive in the mail telling people that there is a delightful picture of them, taken at _____, and available for the surprisingly small fee of $25.  I asked my wife if she had ever bought one.  No, she said: who would want a picture of one's self all hot and sweaty.  Of course, she adds, if it were a group picture, it would make a nice keepsake.  I detect an impending threat, and I am right.

Next year, she says , we will join the walkers as a family team.  I spread more jam on my croissant and say nothing.  I will walk 40 km in a day with a medium load, but only in wilderness.  If I want to be in a crowd, I will take the 200 with their champagne and croissants, not the fifty thousand in liniment, Lycra and Reeboks in the street below.  I decide to change the subject: ‘Look over the road,’ I tell her.

In the park opposite, Sydney's homeless emerged from the undergrowth to pick over the discarded clothing.  Two of the better organised had a long pole that they used to drag the more attractive items out of the trees along the road's edge.  Still, now that summer is coming, they will have less need of extra clothes.


Saturday, 21 September 2019

When the going gets tough...

... the tough go shopping. This is an excerpt of chapter 6 in the same project, and by now, the perceptive reader should have worked out the thrust...


The convicts in general had suffered much through want of clothing and bedding. Indeed, during the late harvest, several gangs were seen labouring in the fields, as free of clothing of any kind as the savages of the country.
—David Collins, An Account of the English Colony in New South Wales, volume 2, 102.

As a rule, everybody needed clothes, and there were set rations, if you were dependent on the Crown. As early as 1804 (though the rules were probably older), the clothing to be provided to convicts was laid down in regulations:

The following Proportion of Cloathing will be issued in future to those at Public Labour, about the 25th of December and the 4th June annually, when the Store will allow of that Distribution viz.
December for each Man 1 Frock, 1 Shirt, 1 Pair of Trowsers, 1 Pair of Breeches, and 1 pair of Shoes;
June For each Man 2 Jackets, 2 Shirts, 1 Pair of Trowsers or Breeches, 1 Hat, and 2 Pair of Shoes. [1]

Just over a year later, there was an issue of “slop clothing” in Sydney. This was a common term in the Royal Navy and also in the colony, where slop or slops meant generic clothing. In 1805, readers of the Gazette saw that there was to be an issue of “Slop Cloathing”:

To Overseers—One Pair of Shoes, two Shirts, one Pair of Trowsers, and a Hat.
To Male Prisoners—A Frock, Shirt, Pair of Trowsers, and Hat.
To Female Prisoners at Public Labour—A Jacket, Petticoat, Shift, Cap, Handkerchief, and Pair of Stockings.
The former Orders, forbidding the Purchase or Disposal of Slop Cloathing issued to Prisoners at Public Labour, remain and continue in force. [2]
Anna Lewin’s advertisement: many items under one roof.  [3]

The honest folk, those not entitled to a handout of slops from the government, went to shops like the one run by Anna Lewin the wife of painter John Lewin. This carried many products (although the reference to ‘gunpowder’ means a type of tea that resembles gunpowder, not the stuff used in muskets).

No shopkeeper could afford to be a specialist when cargoes took three to six months to arrive, or even more, and they would buy anything that would sell. The three advertisements that follow appear in this order on the same page in a single issue of The Sydney Gazette and New South Wales Advertiser, in January 1810. [4]

For Sale by Thomas Abbott, Corner of Barrack Row, frilled shirts 7s. each, Bandanna handkerchiefs 3d. per piece; plain shirts 6s. 6d. each, good tobacco 2s. 3d. per lb. by the basket, sugar 13d. per lb. by the bag, and 12d. per lb. by the ton, yellow soap 2s. 3d. per lb. superfine broadcloths 10s. per yard; printed cambrick by the piece 6s. per yard, check shirts 7s. each, longcloth, 26 yards to the piece, at £7, coffee and tea, flat irons and iron pots 7d. per lb. threads by the lb. and tapes by the dozen, and a variety of other Articles…

John Driver in Chapel Row had even more varied stock:

…Irish linen coarse and fine, black cambrick and capital bombazeens for mourning dresses, toys in great variety, artificial flowers, ladies’ coloured silk bands and tassels, ear and finger-rings, gold lace, knives and scissars, gilt, shirt, and cambrick buttons, gloves, stockings, spy-glasses, writing, paper, pins, needles, thread, sewing cotton, best Hyson tea, common ditto, soap, vinegar, decanters, wine glasses, rummers, tumblers, dishes, plates, mugs, basons, black and coloured silk handkerchiefs, muslin ditto, veils, cambrick muslins,…India muslin, large elegant shawls of superior quality, shoes and boots, sugar candy, pepper, ginger, beans, dried fruits, and many other articles…

Michael Hayes was a leather specialist, but like the other merchants, he was willing to sell anything else that could be obtained, and soon after this advertisement appeared, he was also allowed a wine and spirit licence.

ON Sale, at the warehouse of M. Hayes, an extensive assortment of Leather; consisting of Morocco and Spanish coloured skins, English tanned seal leather and wax calf skins, seal skins, cordovan, brown and white sheep skins, Hessian boot legs boots and shoes, boot top leather, ladies and children’s shoes of all colours, russet calf skins for ladies’ shoes; Also, a variety of other Goods, consisting of cloths, prints, linens, stuffs, calicoes, shawls, teas, sugar, wines, &c. &c. as well as a variety of brass wares.

Over time, some merchants began to specialise, and by the 1840s, much of George Street in Sydney was given over to shops. Louisa Meredith said it was about a mile and a half (2 km) long, with good shops offering all sorts of merchandise.

One long street traverses its whole length, about a mile and a half, full of good shops exhibiting every variety of merchandise; and in the afternoon, when the ladies of the place drive out, whole strings of carriages may be seen rolling about or waiting near the more “fashionable emporiums,” that being the term in which Australian shopkeepers especially delight. [5]

I have heard it asserted (but cannot now find a source for it) that in the early days, men working in paddocks would wear just a long shirt in order to keep cool. An article on the governor’s expenses, taxes and the cost of rum in The Monitor in 1828 refers to agricultural workers’ removing their shirts when labouring.

…the shearers of the harvest of this Colony…when, sweating under an almost vertical sun, with their backs burnt (as we have often seen them) as deep in colour as a cake of patent chocolate…the above-mentioned mahogany-backed shirtless reapers…[6]



[1] The Sydney Gazette and New South Wales Advertiser, 15 January 1804, 1, http://trove.nla.gov.au/ndp/del/article/625985
[2] The Sydney Gazette and New South Wales Advertiser, 3 February 1805, 1, http://trove.nla.gov.au/ndp/del/article/626609
[3] The Sydney Gazette and New South Wales Advertiser, Sunday 12 June 1808, 2, http://trove.nla.gov.au/ndp/del/article/627525
[4] The Sydney Gazette and New South Wales Advertiser, 21 January 1810, 4, http://trove.nla.gov.au/ndp/del/article/627915
[5] Louisa Ann Meredith, Notes and Sketches of New South Wales, 38.
[6] The Monitor (Sydney), 14 May 1828, 4, http://trove.nla.gov.au/ndp/del/article/31759959

Tuesday, 10 September 2019

What geologists think, part 3

8. The standard principles of science

These are ideas that all scientists just assume, but they are rarely stated explicitly for students or the public. There is enough information here to tell you what each idea is about, and you will find enough terms to let you look the idea up, if you need to. There are lots of ins and outs, and working scientists spend their lives mastering them. They will, I hope, recognise that this is Science Lite.

Atoms and molecules

All matter is made up of atoms, and the properties of any piece of matter will depend on what atoms are present, and how they are arranged and connected. Many atoms join up to form regular frameworks that we call crystals. Sometimes, atoms join into tight standard groups, like water, quartz, salt and sugar. We csll these groups molecules.

The laws of thermodynamics

For general purposes, heat flows from hot to cold, perpetual motion is impossible, and there is no such thing as a free lunch. By the way, if you want to drive a politician or an arts administrator to distraction, ask him or her to explain (or even just to state) the second law of thermodynamics. Trust me: it matters!
A good many times I have been present at gatherings of people who, by the standards of the traditional culture, are thought highly educated and who have with considerable gusto been expressing their incredulity at the illiteracy of scientists. Once or twice I have been provoked and have asked the company how many of them could describe the Second Law of Thermodynamics. The response was cold: it was also negative. Yet I was asking something which is the scientific equivalent of: Have you read a work of Shakespeare’s?
—C. P. Snow, Rede Lecture The Two Cultures and the Scientific Revolution (1959).
 If you want a simple version, it says that differences in temperature, pressure, and density tend to even out, after a while. More detailed discussion involves entropy The simplest available version of that: entropy is a thermodynamic function that measures randomness or disorder. If you like, entropy is a measure of untidiness.
 
Most of the principles of science are what scientists call counter-intuitive. In lay terms, they seem to go against our gut reaction; the earth as we experience it looks flat, and our intuition tells us the sun and moon circle around us once a day, but ignoring intuition, all scientists agree that the world is a globe, we orbit around the sun, and the moon orbits around us once a month.

Entropy is slippery, rather than counter-intuitive, and you have to note the qualifications which limit entropy to inside a closed system. Under those conditions, entropy, or disorder, increases, which is how scientists say that over time, everything gets more random, more dispersed.

There can be no exceptions to the rule that entropy, the disorder of things, always increases, but life, at a local level, can be an anti-entropy agent, making some things more ordered at a local level, even as entropy is increasing on a larger scale. In simple terms, animals and plants gather up and concentrate certain elements in our bodies.

Across the universe, every change leads to an increase in the total entropy, but the delight lies in the details, and a lot of geological science comes down to explaining how, on a local level, the process of concentration in elements or minerals is driven.
If [your pet theory of the universe] is found to be contradicted by observation—well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation.
—Sir Arthur Stanley Eddington, The Nature of the Physical World (1928), chapter 4.

Conservation of mass and energy

In simple terms, matter and energy can neither be created nor destroyed. There is No Such Thing As A Free Lunch.

Equilibrium

As a rule, things are in balance, but that is not the same as saying they are unchanging. The number of oxygen molecules in an open jar may vary slightly over time, as molecules whizz in and out, but at any practical level, the entries and exits cancel each other out. If I have crystals of salt sitting in a saturated brine solution, some of the chloride and sodium ions in solution may attach to the crystals, but on average, just as many ions will leave the crystals. We say the solid and the solution are in dynamic equilibrium.

The law of large numbers

There is no such law, but it is convenient to pretend that it exists. Given time, every atom of a sample of radioactive carbon-14 will break down. We cannot say when a given atom will decay, but with large numbers of atoms, we can say that half of all of the atoms that we start with now will have decayed if we come back in 5730 years from now. We say that carbon-14 has a half-life of 5730 years.

Evolution

Evolution also hangs on large numbers. You won’t evolve, I won’t evolve, but our species, like every other species, does evolve. Don’t worry: some of your genes will carry forward, and some of them may be more common in a future population.

(I anticipate, for example, that in a thousand years, the descendants of today’s Australians will have a skin color darker than mine, due to the selective effects of melanoma.)

(Note that this can  be negated because humans, uniquely in an evolving world, can apply social changes to limit selection effects.)

Falsifiability

Every part of science is able to be falsified by evidence, and if some idea can’t be tested and potentially falsified, it just isn’t science. That doesn’t mean science is all false, it just means every assumption is always considered open to testing and being found wrong.

If we found dinosaur fossil bones and human fossil bones in the same rock, this would mean we probably had to revise large parts of what we think we know about geology and biology, though the first step would be to check carefully that somebody hadn’t just pulled off a hoax.

Scientists are always on the alert for contradictions like that, even though they don’t really expect to find any. One way to become a famous scientist is by finding a red-hot contradiction to what everybody believes.

Ockham’s Razor

Then again, maybe we wouldn’t need to revise anything. William of Ockham made it a lot more complicated, but his basic notion was that if there are two possibilities, you should take the simpler one. If we found human and dinosaur fossils in a single rock, a simpler explanation would be fraud. We would at least look for evidence of fraud first, but if there was truly no evidence of fraud, it might be time to start a rethink.

9. Caveats

I am not a geologist, but I know how to think, where to look, and what questions to ask. My undergraduate studies were mainly in the areas of botany and zoology, so I may, from time to time, be in error. As a professional science writer, I am used to checking my facts, but even when I get the latest opinions there is still one gotcha remaining.

Science changes, and geological science does change—and I saw it happen. When I was an undergraduate, I picked up one year of formal geology training, enough to appreciate that the rocks yield the soil that my precious plants flourish in, plants that feed my equally precious animals.

One day, one of our geology lecturers urged us to attend certain sessions of ANZAAS, the Australian and New Zealand Association for the Advancement of Science. “Listen to Sam Carey,” he told us. “He’s quite mad: he thinks the continents are moving.”

That was in 1962, and I did indeed hear Sam Carey talking about such wild ideas. He seemed to make a reasonable case, except that we all knew the idea was crazy. Just three years later, plate tectonics was all the go.

In fairness, Sam Carey was only partly right, because his notion was based on some false assumptions, but the key thing to note is this: in 1962, moving continents was madness, by 1965, it was pretty much the orthodox model.

I have tried in this book to stay with the best and safest bits of orthodoxy, but at any time, that which was orthodox can be defeated of overturned by a simple paradox. One new discovery is all it takes, as T. H. Huxley said while discussing historical work on the spontaneous generation of life:
But the great tragedy of science—the slaying of a beautiful hypothesis by an ugly fact—which is so constantly being enacted under the eyes of philosophers, was played almost immediately, for the benefit of Buffon and Needham.
—T. H. Huxley, Presidential address to the British Association in September, 1870.
My book (meaning Not Your Usual Rocks, still to be published) is about the facts—though I will later discuss a maverick theory about the origins of oil. I don’t believe it, but it is both entertaining, and instructive to consider as a way of seeing how science works.



By the time you are done, all of these will make perfect sense.

My book wins a prize.

Note: the book won the prize, not me, though I was part of the team at the National Library of Australia.

The guilty parties include:

  • Author: me;
  • Commissioning Publisher: Susan Hall;
  • Editor: Joanna Karmel;
  • Designer: Stan Lamond;
  • Illustrator (cartoons): Tony Flower;
  • Image coordinator: Emma Posch;
  • Production coordinator: Melissa Bush;
  • Indexer: Joanna McLachlan.

The award was part of the Educational Publishing Awards 2019, and it came under this long-winded category:

Student resource: Arts/Science/Humanities/Social Sciences/Technologies/Health and Physical Education/Languages

Anyhow, here's what it looks like, front and back:











Tuesday, 3 September 2019

What geologists think, part 2.

As I said before, I'm cleaning up all the unfinished projects, and Not Your Usual Rocks is at the top of the pile.

You'd probably be better off starting with Part 1, but there are two by-the-ways

1. The photos that aren't credited are mine, and they are all
© Peter Macinnis, Creative Commons Attribution 4.0 International.
That means you can use them for non-commercial purposes with attribution, but while I squash thieves like the people at the Charles Sturt Memorial Museum, I will happily provide high-res copies to people who ask.

2. The locations reflect a lot of travel, but you can probably work out roughly where I live, if you live near me. If you do, say g'day!

6. All of the effects we see in the geology can be explained

Basically, all the things that we see in the world can be explained by the forces we see operating today. Geologists call this principle uniformitarianism, and it just means the natural laws and processes that we see shaping the earth today are the same ones that shaped the past.

In other words, we don’t work on the principle that there used to be wizards and witches who moved the rocks around; there were no fire-breathing dragons that made the lava melt. We do not need to assume the existence of pixies driving Stealth Bulldozers, poltergeists with geological interests, malignant mammoths, whimsical aliens or lost civilisations.

Continents move, floating on the surface of the planet; earthquakes happen; rocks form, weather and erode; rocks get pushed up; others get pushed down and buried, and so on. On a smaller scale, sediments get washed by water, blown by winds, and sometimes, pushed by glaciers.

When weight is applied to the existing surface, in the form of glaciers or any other way, the earth’s crust behaves like a small raft that an elephant has boarded: the rocks sink. On the other hand, when glaciers melt, the earth springs back up again, and this is currently happening in Scandinavia which was relieved of a lot of weight, about 10,000 years ago.

The rocks, even the not-your-usual rocks, keep to the following principles.

7. There are standard rules of geology

Sometimes, what you see may appear to be contrary to these rules, but if you think that, it usually means you haven’t thought hard enough. The apparent contradictions emerge only because you are unaware of the other rules that applied in a particular place. With enough thinking, you can generally explain what you see.

Rocks are usually laid down in flat layers.

It is a fairly safe rule that sedimentary rocks form flat, parallel beds, because the sediments are washed or blown into some sort of basin, and the first material fills in the gaps and crevices, leaving a flat surface. The effects of currents (or winds) and gravity keep the top fairly flat.


Horizontal strata, Bungle Bungles, Western Australia

An illustration from Charles Lyell’s The Student’s Elements of Geology (1871), page 17, showing how irregularities in an underlying surface are filled in, slightly contradicting Steno. [Public domain]
Then again, some beds can be laid down on a slope. This is called cross bedding or current bedding, and we will look at it in more detail later. Cross bedding can be distinguished from beds that have been tilted later by looking at the horizontal beds above and below.

 
Cross bedding in Hawkesbury sandstone, Old Man’s Hat, North Head, Sydney, Australia
There can be traps for the unwary when it comes to igneous rocks. If the rock arrives as lava, streaming down the flank of a volcano, some of the lava cools and becomes solid, leaving a sloping skin of rock. Nothing is inexplicable.


Eroded remnants of an old volcano near Cape Palliser, North Island, New Zealand.

Younger rocks usually lie on top of older ones

They are always laid down that way, but there are a couple of notable exceptions. Basalt sometimes pushes up through sedimentary (or other) rocks to form a dyke. If the dyke reaches the surface, it flows out over the landscape (which is why it is called a flow. A flow is always younger than the rocks it lies on top of, and older than any rocks which are found above it.

Sometimes, the basalt pushes in between two layer of rock, forming what is called a sill, but the basalt remains younger than the rocks that lie on top of it. How do we know? We look for contact metamorphism, above and below.

The other exception to youngest-on-top comes when rocks bend, and fold, and sometimes (rarely), overfold, so that the usual age order is reversed in a limited area.

In less extreme cases, horizontal beds may just be tilted up and eroded away, leaving tilted rocks behind. If the land sinks at this point, new sediments wash in to start a new age of rock building.
In an area where there are active volcanoes, lava may pour out and flow across the countryside, laying fairly flat layers—except, as mentioned above, on the flanks of the volcanoes, where sloping beds will form.

The Columbia River forms the border between Washington and Oregon in the USA, flowing through a valley carved through a massive series of basalt flows.
  
There can be gaps in the geological record in any place

On my home territory, near Sydney on Australia’s east coast, the rocks are Triassic in age. If you drill straight down you will come eventually to Permian rocks, the coal measures that are exposed around the margins of what we call the Sydney Basin. You find coal at Newcastle, Wollongong, Lithgow and other places. Coal also used to be mined on the very shores of Sydney harbour, but they had to sink a shaft quite a long way down, all the way to the Permian rocks.

In theory, if we keep going down, we should next move into rocks from the Carboniferous, but these layers are missing in my favourite walking area, in the Budawang Ranges, west of Nowra, south of Sydney. We meet up with tilted Devonian metamorphic rocks instead. It looks as though we are missing 100 million years (or more) of geological history.

Any rock-hound will tell you this is an unconformity, and hazard a guess that the Devonian rocks were deeply buried and covered with Carboniferous rocks, but that the earth and its rocks moved hugely, and any Carboniferous rock was eroded away, leaving ribs of tough Devonian stone across the land in the early Permian era. We really can’t be sure there were ever any Carboniferous rocks, but it is quite likely that they came and went, leaving no trace.

Later, the land all sank deep into a sea of some sort of cataclysm. In the Budawang ranges, the lowest layer of the Permian rocks is a conglomerate containing very large boulders, telling us that the first deposits in that part of the basin were laid down in a huge flood.


At Myrtle Beach, on the south coast of NSW, this conglomerate layer is missing, suggesting that the oldest Permian sediments there were laid down at a different time. It may have been a few years, more probably it was a few millennia—or even quite a few millennia. Geology never scurries.

Myrtle Beach, south coast of NSW. The sloping beds below are pointing to 1 o’clock,
and the hand (top left) spans a gap of about 100 million years in the geological record.



There is also a simpler sort of time gap, much harder to identify, called a disconformity. This happens when sediments stop being delivered for a while, but we can largely ignore these hiccups for the moment. We now have the basic background to understand a bit of slightly more detailed geological history. 

The laws and principles of geology

Nicolas Steno started it. Here is a modern version that conveys his thinking in the language we use today.

* Steno’s Law of Superposition says that in a sequence of strata, any stratum is younger than the sequence of strata on which it rests, and is older than the strata that rest upon it.

* Steno’s Law of Original Horizontality says that strata are deposited horizontally and then deformed to various attitudes later. That is, undisturbed true bedding planes are nearly horizontal, though we need to note here that cross-bedding is possible where sandhills or sandbanks are being formed.

* Steno’s Principle of Lateral Continuity: strata initially extend sideways in all directions. That is, every outcrop in which the edges of strata are exposed demands an explanation, and strata on two sides of a valley represent erosion of the rock between.

* Steno’s Principle of Cross-cutting Relationships: anything that cuts across layers post-dates them. This applies particularly to igneous intrusions such as dykes. Aside from Steno’s principles, geologists accept the following notions:

(1) an intruding rock is younger than the rock it intrudes into;

(2) a fault is younger than the rock which is faulted;

(3) any pieces of ‘foreign’ rock included within a rock must be older than the rock they are found in; and

(4) William Smith’s principle of fossil succession.

We will come to that in a moment, but geology was only possible because of James Hutton. He had made enough money from an ammonium chloride factory to be able to retire from work and study geology.

Hutton was an old friend of Joseph Black, the first scientist to distinguish heat from temperature, and also of James Watt (the steam engine maker), so it is no surprise to discover that Hutton assumed that all earth activity was due to what he called the earth’s ‘heat engine’. But most importantly, he said that “…The past history of our globe must be explained by what can be seen to be happening now”.

He emphasised the igneous origin of many rocks (unsurprisingly, given that he came from Edinburgh, where igneous rocks rear up all around the town). Unfortunately, the French Revolution was happening, so the public in Britain was less than enthusiastic about Hutton’s revolutionary notions. They were not only unready for his ideas, they were unwilling to accept them, but the scene was now set.

John Playfair was probably one of the few people to combine geometry with geography and geology. Trained in mathematics at a time when geology had not yet been invented, Playfair was necessarily largely self-taught. Like James Hutton, Playfair was exposed to the stimulating geology of Edinburgh, which would have assisted him in his work.

He also invented geomorphology, giving us ‘Playfair’s Law’, which states that rivers cut their own valleys. Then he gave us the modern concept of grade when he asserted that the angle of slope of each river shows an adjustment towards a balance between the velocity and discharge of water on one hand, and the amount of material carried on the other.

Playfair also made the work of Hutton more accessible when he published his Illustrations of the Huttonian Theory of the Earth in 1802. He explained the rock cycle of repeated weathering, erosion, deposition and solidification in simple terms: notice, with a modern eye, how he covers weathering, erosion, sedimentary rocks forming in the sea and uplift.

The series of changes which fossil bodies are destined to undergo, does not cease with their elevation above the level of the sea; it assumes, however, a new direction, and from the moment that they are raised to the surface, is constantly exerted in reducing them again under the dominion of the ocean. The solidity is now destroyed which was once acquired in the bowels of the earth; and as the bottom of the sea is the great laboratory where loose materials are mineralized and formed into stone, the atmosphere is the region where stones are decomposed, and again resolved into earth.
—John Playfair, Illustrations of the Huttonian Theory of the Earth, 1802, 109.

The idea of igneous rocks came later. Playfair’s ideas only gained wide acceptance after Charles Lyell added Playfair’s ideas into his Principles of Geology, but we have left out William Smith, an orphan who was set to work early as a surveyor for the new canals that were beginning to cross the British countryside, so industrialists could haul goods from place to place.
 
These canals required digging into the ground, and they had to cut tunnels through hillsides. This all gave Smith first-hand chances to observe and classify the many rock types as they are seen in fresh unweathered exposures. Most importantly, he noticed how strata were typified by fossils, and he pointed out that the same stratum could be identified at a considerable distance by the fossils it contained.

In 1816, Smith published his ideas, accompanied by a coloured geological map, and made the point that, given the law of superposition, the fossils in the strata gave us a view of the history of life on earth. Now the way was fully prepared, and Charles Lyell’s Principles of Geology could be released in the early 1830s, just in time for Charles Darwin to take them with him on the voyage of HMS Beagle. That meant he was prepared to unravel in full detail the reasons why life actually possessed a history on earth.

That is how science weaves itself into a web, but it also involves cycles.

Geological science is also science, and there are some principles of science, as well. I will get to those in part 3.