Friday, November 30, 2012

How many hours were in a dinosaur's day?


Real dinosaurs lived in a world that would have been different to ours in more than the obvious ways.

The 24-hour clock is locked into our mammalian biology, our technology and our culture. But it hasn't always been that way.

The length of an Earth day has been increasing slowly throughout most of the Earth's 4.5-billion-year history, says Dr Rosemary Mardling, mathematical scientist at Monash University, and it all has to do with the Moon.

"The reason is that the Moon is attempting to slow down the spin of the Earth. The Earth was spinning very much faster when the Moon was formed," says Mardling.

Back when the Moon was formed the length of an Earth day was a very brief two to three hours, and a much closer Moon was orbiting the Earth every five hours.

So how did the Moon slow us down? It has to do with gravitational force and the transfer of angular momentum.

"If someone was sitting on a chair that could spin and you tried to slow them down with your hand, they would slow down a little bit and you'd be flipped around a bit. You'd get some angular momentum."

And that's what is happening with the Earth-Moon system. Much like the hand interrupting the spinning chair, the gravitational pull of the Moon exerts a force on the Earth that transfers angular momentum from the spin of the Earth into the orbit of the Moon.

"In doing so, the Earth slows down a little bit and the Moon moves away from the Earth," says Mardling.

We can measure the speed of the Moon's retreat — reflective panels on the Moon allow for fine calibrations that show that it's currently moving away one to two centimetres a year.

We also know that the spin of the Earth is slowing.

"The spin down rate is very slow," says Mardling, "It's about two milliseconds per century. So the Earth's day is getting longer by a 500th of a second every century"

In the time of the dinos

So would the day length during the age of the dinosaurs have been 21 hours?

"The dinosaurs were around 100 million years ago, which at the current rate [of day lengthening] adds up to 2000 seconds, which is less than an hour."

But while the lengthening of the day adds up, "the spin down rate was probably greater in the past," she adds.

Geological evidence for increasing day length can help us pin this time down more accurately. Tidal records laid down in ancient estuaries can show daily, monthly and seasonal cycles in alternating deposits of sand and silt. They indicate that 620 million years ago the day was 21 hours, says Mardling.

Since the dinosaurs lived during the Mesozoic era, from 250 million years ago to 65 million years ago, day length would have been longer than 21 hours and probably closer to 23 hours.
At that time the Moon would have been closer to the Earth too. So the world the dinosaurs lived in would have been different to ours in more than the obvious ways, she says.

Earthquakes and day length

Significant earthquakes can also affect the length of the day, but only very slightly.
They do so be changing the Earth's "moment of inertia" which describes how mass is distributed inside the Earth. The principal of conservation of angular momentum means that a change to the moment of inertia results in a change to the spin rate.

"Imagine the Earth is made of lots of little bricks. You can measure the position of each brick and its position from the rotation axis of the Earth. If you squared that distance, multiplied it by the mass of the brick and then you added it all up over all the bricks, you would get the moment of inertia.
If you move the bricks around a little bit you get a different answer, and that's what can happen during some very large earthquakes.

The future

The Moon and Earth's celestial dance theoretically will take billions of years to end.

"This process finishes when the length of the day is the same as the length of the (lunar) month," says Mardling, who once worked this out to be around 45 (current Earth) days.

This means that the Moon will take 45 days to orbit the Earth and the Earth will take 45 days to complete a rotation that currently takes 24 hours.

"At that point the Earth will always show the same face to the Moon, as the Moon already does to us."

This will occur when the Moon has "spun down" the Earth, says Mardling.

"We spun down the Moon a long, long time ago because it is so much less massive than the Earth".
"However", says Mardling, "it's such a ridiculously long time away that by then the Sun will have become a red giant."

And if humans are still around then we'll have bigger things to worry about than day length.

Dr Rosemary Mardling is a senior lecturer at Monash University's School of Mathematical Sciences. She studies the dynamical evolution of stellar and planetary systems. Dr Mardling spoke to Kylie Andrews.

Monday, November 26, 2012

Giants




London, British Library, Cotton Claudius B.iv, f. 13r, Giants, the Hexateuch.

The converted Anglo-Saxons considered Scripture to be the most reliable source of information, literally accurate in all its details. Beginning with Genesis, the book of the Old Testament most often reproduced in Anglo- Saxon England, we read that "giants were on the earth in those days." This verse merited illustration in the Hexateuch, an extensively illuminated volume containing the first six books of the Old Testament, introduced by a prefatory letter by Ælfric.  These figures fill their half-page frame. They are logically the largest among the thousands of figures in this massive volume, as if drawn to scale within the manuscript, but they are otherwise not particularly fearsome or monstrous. Quite to the contrary, they gesture to one another in a restrained manner as they seem to hold a polite conversation. Their modes of dress, hair and beard in no way distinguish them from the rest of the biblical characters. There are numerous other references to giants and other monsters in the Old Testament, with Goliath as the most famous example. While twenty-first-century readers might scoff at the notion of turning to the Bible for scientific information about the races of the Earth, this was still being done well into the nineteenth-century, when prolific essayist and novelist Charles Mackay wrote that Acts 17:26 (God made of one blood all nations of the earth.) was in common usage by "preachers, professional lecturers, salaried philanthropists, and weak-minded women . . . together with the philosophers and the strong-minded women . . . and all the multitude of theorists" in discussions of the human races. 


Giants also appear as a common Anglo-Saxon poetic trope. As part of a semi-mythical history, they were credited with having built the monumental stone structures which remained from prehistory and the Roman occupation of Britain.  The Ruin describes one such building in its opening lines: 

Splendid is the rampart, broken by fate;
the burg burst apart, the work of giants crumbles.  

This enta geweorc, this work of giants, was considered to be too great to have been the product of human labor. The trope of enta geweorc served to distance the Anglo-Saxons from the entirely human past of Britain. Of course, all the Christian and, indeed, Jewish and Moslem world would have had the Biblical texts which may have inspired some of these later accounts, and yet "there is something distinctly Anglo-Saxon about this fascination with giants conjoined to the formation of alienated, human identities." In an Old English homily, giants were connected with two other traditions: Classical antiquity, kept alive through the monastic copying of texts, and Germanic religion, still very much alive in the living memories and beliefs even of longconverted groups. Biblically sanctioned giants are used by an Anglo-Saxon homilist as an explanation for the otherwise inexplicable worship of beings outside the Christian context: 

The devil ruled men in Middle-Earth, and all that time he worked against God and God's servants, and he raised himself over all, and so the heathen men would say that the gods must be their heathen leaders, just as was Hercules the Giant and Apollo, for whom they forsook the great God; Thor also and Odin, whom heathen men praise exceedingly.

Friday, November 23, 2012

Aussie scientists un-discover Pacific island


What the researchers didn't see: conspiracy theories suggest it was a phantom island added in the middle of last centruy

A South Pacific island identified on Google Earth and world maps does not exist, according to Australian scientists who went searching for the mystery landmass during a geological expedition.
The sizeable phantom island in the Coral Sea is shown as Sandy Island on Google Earth and Google maps and is supposedly midway between Australia and the French-governed New Caledonia.

The Times Atlas of the World appears to identify it as Sable Island. Weather maps used by the Southern Surveyor, an Australian maritime research vessel operated by the CSIRO, also say it exists, according to Dr Maria Seton.

But when the Southern Surveyor, which was tasked with identifying fragments of the Australian continental crust submerged in the Coral Sea, headed to where the island was supposed to be, it was nowhere to be found.

"We wanted to check it out because the navigation charts on board the ship showed a water depth of 1400 metres in that area - very deep," says Seton of the University of Sydney, after the 25-day voyage.

"It's on Google Earth and other maps so we went to check and there was no island. We're really puzzled. It's quite bizarre."

"How did it find its way onto the maps? We just don't know, but we plan to follow up and find out."

Deliberate mistake?

News of the invisible island sparked debate on social media, with tweeter Charlie Loyd pointing out that Sandy Island is also on Yahoo Maps as well as Bing Maps "but it disappears up close".



On www.abovetopsecret.com, discussions were robust with one poster claiming he had confirmed with the French hydrographic office that it was indeed a phantom island and was supposed to have been removed from charts in 1979.

Another claimed: "Many mapmakers put in deliberate but unobtrusive and non-obvious 'mistakes' into their maps so that they can know when somebody steals the map data."

Google says it always welcomed feedback on a map and "continuously explore(s) ways to integrate new information from our users and authoritative partners into Google Maps".

"We work with a wide variety of authoritative public and commercial data sources to provide our users with the richest, most up-to-date maps possible," a Google spokesman said.

"One of the exciting things about maps and geography is that the world is a constantly changing place, and keeping on top of these changes is a never-ending endeavour."

The Australian Navy's Hydrographic Service - the department responsible for producing official nautical charts - told Fairfax media it took the world coastline database "with a pinch of salt" since some entries were old or erroneous.

Wednesday, November 21, 2012

'Toxic sea' led to Devonian extinction



The researchers say the crustacean was exceptionally well preserved by a combination of processes (Kliti Grice)

Anna Salleh
ABC


Analysis of a 380-million-year-old crab-like fossil from Western Australia has painted a gruesome picture of the events leading to one of Earth's major mass extinctions. 

Climate change and a devastating meteorite have both been fingered as causes for the decimation of marine life during the late Devonian period.

But research published in a recent issue of the journal Geology suggests the extinction occurred as a result of a toxic ocean, devoid of oxygen.

"We think there was anoxia, where toxic levels of hydrogen sulfide are released into the zone where light penetrates into the ocean," says organic geochemist Professor Kliti Grice, of Curtin University.
"A modern analogue of the conditions that existed at this time is the Black Sea."

Grice and colleagues, including PhD student Ines Melendez, reached their conclusions after analysing a 380 million-year-old crab-like fossil from the Gogo Formation in Canning Basin, Western Australia.

They identified chemical remains of various biological molecules, known as biomarkers, that helped paint a picture of environmental conditions at the time.

The researchers found a derivative of cholesterol, confirming for the first time that the fossil was the remains of a crustacean.

And they found biomarkers of photosynthesising phytoplankton, which the crustacean would have fed on.

Grice and colleagues also found biomarkers of green sulfur bacteria, also called Chlorobi which would have photosynthesised using hydrogen sulfide instead of water.

She says Chlorobi made a special pigment that enabled them to capture light of longer wavelengths, making it possible from them to survive in the murky waters beneath the bloom of phytoplankton.
"The ocean became stratified with an oxygen layer and an anoxic layer, and where the Chlorobi lived, right at the point where hydrogen sulfide is abundant," says Grice.

Last but not least, the researchers found biomarkers of sulfate-reducing bacteria, which would have lived even deeper down in the ocean and survived by degrading organic matter using sulfate instead of oxygen. This would have been the original source of the hydrogen sulfide on which the Chloribi thrived.

Grice says the condition of the ocean was identical to that which occurred during a later mass extinction at the end of the Permian, the largest extinction event in the past 600 million years.
The crustacean may have sunk to its death at the bottom of the ocean, intoxicated by hydrogen sulphide, says Grice, where it was preserved for hundreds of millions of years.

Preservation

The researchers say the 15-centimetre wide crustacean was exceptionally well preserved by a combination of processes.

Grice says the hydrogen sulphide chemically preserved the muscle tissue in the crustacean, as well as organic molecules from the green sulfur bacteria.

"The molecules and the fossil were all preserved by the same mechanism, and that has never been reported in such detail," says Grice.

The fossil was further preserved by a calcium carbonate encasement built by the sulfate-reducing bacteria.

The levels of biomarkers from sulfate-reducing bacteria were particularly high in this encasement, Grice says.

The research was funded by the Australian Research Council.

Tuesday, November 20, 2012

Giant Sequoias


Forest Giant

A tree-climbing scientist and his team have learned surprising new facts about giant sequoias by measuring them inch by inch.

By David Quammen
Photograph by Michael Nichols
 
On a gentle slope above a trail junction in Sequoia National Park, about 7,000 feet above sea level in the southern Sierra Nevada, looms a very big tree. Its trunk is rusty red, thickened with deep layers of furrowed bark, and 27 feet in diameter at the base. Its footprint would cover your dining room. Trying to glimpse its tippy top, or craning to see the shape of its crown, could give you a sore neck. That is, this tree is so big you can scarcely look at it all. It has a name, the President, bestowed about 90 years ago by admiring humans. It’s a giant sequoia, a member of Sequoiadendron giganteum, one of several surviving species of redwoods.

It’s not quite the largest tree on Earth. It’s the second largest. Recent research by scientist Steve Sillett of Humboldt State University and his colleagues has confirmed that the President ranks number two among all big trees that have ever been measured—and Sillett’s team has measured quite a few. It doesn’t stand so tall as the tallest of coast redwoods or of Eucalyptus regnans in Australia, but height isn’t everything; it’s far more massive than any coast redwood or eucalypt. Its dead spire, blasted by lightning, rises to 247 feet. Its four great limbs, each as big as a sizable tree, elbow outward from the trunk around halfway up, billowing into a thick crown like a mushroom cloud flattening against the sky. Although its trunk isn’t quite so bulky as that of the largest giant, the General Sherman, its crown is fuller than the Sherman’s. The President holds nearly two billion leaves.

Trees grow tall and wide-crowned as a measure of competition with other trees, racing upward, reaching outward for sunlight and water. And a tree doesn’t stop getting larger—as a terrestrial mammal does, or a bird, their size constrained by gravity—once it’s sexually mature. A tree too is constrained by gravity, but not in the same way as a condor or a giraffe. It doesn’t need to locomote, and it fortifies its structure by continually adding more wood. Given the constant imperative of seeking resources from the sky and the soil, and with sufficient time, a tree can become huge and then keep growing. Giant sequoias are gigantic because they are very, very old.

They are so old because they have survived all the threats that could have killed them. They’re too strong to be knocked over by wind. Their heartwood and bark are infused with tannic acids and other chemicals that protect against fungal rot. Wood-boring beetles hardly faze them. Their thick bark is flame resistant. Ground fires, in fact, are good for sequoia populations, burning away competitors, opening sequoia cones, allowing sequoia seedlings to get started amid the sunlight and nurturing ash. Lightning hurts the big adults but usually doesn’t kill them. So they grow older and bigger across the millennia.

Another factor that can end the lives of big trees, of course, is logging. Many giant sequoias fell to the ax during the late 19th and early 20th centuries. But the wood of the old giants was so brittle that trunks often shattered when they hit the ground, and what remained had little value as lumber. It went into shingles, fence posts, grape stakes, and other scrappy products. Given the difficulties of dealing with logs 20 feet thick, broken or unbroken, the trees were hardly worth cutting. Sequoia National Park was established in 1890, and automobile tourism soon showed that giant sequoias were worth more alive.

One thing to remember about them, as Steve Sillett explained to me during a conversation amid the trees, is that they withstand months of frigid conditions. Their preferred habitat is severely wintry, so they must be strong while frozen. Snow piles up around them; it weights their limbs while the temperature wobbles in the teens. They handle the weight and the cold with aplomb, as they handle so much else. “They’re a snow tree,” he said. “That’s their thing.”

Among the striking discoveries made by Sillett’s team is that even the rate of growth of a big tree, not just its height or total volume, can increase during old age. An elderly monster like the President actually lays down more new wood per year than a robust young tree. It puts that wood around the trunk, which grows wider, and into the limbs and the branches, which grow thicker.

This finding contradicts a long-held premise in forest ecology—that wood production decreases during the old age of a tree. That premise, which has justified countless management decisions in favor of short-rotation forestry, may hold true for some kinds of trees in some places, but not for giant sequoias (or other tall species, including coast redwoods). Sillett and his team have disproved it by doing something that earlier forest ecologists didn’t: climbing the big trees—climbing all over them—and measuring them inch by inch.

With blessings and permits from the National Park Service, they performed such high-altitude metrics on the President. This was part of a larger study, a long-term monitoring project on giant sequoias and coast redwoods called the Redwoods and Climate Change Initiative. Sillett’s group put a line over the President’s crown, rigged climbing ropes into position (with special protectors for the tree’s cambium), donned harnesses and helmets, and went up. They measured the trunk at different heights; they measured limbs, branches, and burls; they counted cones; they took core samples using a sterilized borer. Then they fed the numbers through mathematical models informed by additional data from other giant sequoias. That’s how they came to know that the President contains at least 54,000 cubic feet of wood and bark. And that’s how they detected that the old beast, at about the age of 3,200, is still growing quickly. It’s still inhaling great breaths of CO₂ and binding the carbon into cellulose, hemicellulose, and lignin in a growing season interrupted by six months of cold and snow.

Not bad for an oldster.

That’s the remarkable thing about them, Sillett told me. “Half the year, they’re not growing aboveground. They’re in the snow.” They grow bigger than their biggest compeer, the coast redwood, even with a shorter growing season.

It was fitting, therefore, that Michael (Nick) Nichols made his portrait of the President in snow. Nick and Jim Campbell Spickler, an expert climber and rigger, came up with a plan. With a crew of assistants and climbers drawn heavily from Steve Sillett’s team, they arrived in mid-February, when the snowbanks along the plowed road were 12 feet high. They rigged ropes on the President and on a tall nearby tree, both for human ascent and for raising cameras. They waited through blue skies, slushy conditions, and fog until the weather changed and the snow came again and the moment was right. They got the shot. (Actually there were many individual shots, assembled as you see on the poster.) By the time I showed up, they were packing to leave.

Nick had spent more than two weeks commanding this operation, composing the image and engineering it from the ground. But before the last ropes came down, he wanted to climb the tree himself. Not to take photos, he explained. “Just to say goodbye.” He put on a harness and a helmet, clipped onto a rope, fit his feet into the loops, clutched the ascender, and up he went.

Once Nick was down, I went up myself—slowly, clumsily, with help from Spickler. Ascending, I braced my feet gratefully against the great trunk. I stood for a moment, with Spickler beside me, on one of the huge limbs. After half an hour, I found myself in the crown of the President, 200 feet above the ground. I saw the big burls at close range. I saw the smooth, purplish bark of the smaller branches. All around me was living tree. I looked up, dizzily, noticing small cracks in the deadwood and channels of cambium that flowed between trunk and limbs like a river of life. I thought: What an amazing place. Then I thought: What an amazing creature.

Next afternoon, with Nick and the others gone, I snowshoed back to the President alone. There had been too much to take in, and I wanted another look. For a while I gaped at the tree. It was magnificent. Serene. It didn’t sway in the breeze; too solid to sway. I wondered about its history. I contemplated its durability and its patience. The day was warmish, and as I stood there, the President released a small dollop of melting snow from a high branch. The snow scattered as it fell, dissipating into tiny flecks and crystals, catching the light as they tumbled toward me.

“Gesundheit,” I said.

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Monday, November 19, 2012

The Rift Valley – Middle East



The hills of northern Galilee, with Mount Hermon in the background.


The Dead Sea: the barren landscape of the western shore. Salt deposits are clearly visible.


In the vicinity of Dan are the springs which form the sources of the River Jordan, fed by water from the snow-capped Mount Hermon to the north-east. From these springs, the waters flow into the Huleh basin where, in biblical times, there was a lake whose Greek name was Lake Semechonitis. From Huleh, 223 ft (68 m) above sea level, the Jordan drops rapidly to the Sea (or Lake) of Galilee (or Chinnereth), which is already 695 ft (212 m) below sea level. The name `Jordan' is probably connected with a root which means `go down', so the name is very appropriate. The descent continues south of the Sea of Galilee, as the river continues to drop towards the Dead (or Salt) Sea whose surface is nearly 1,300 feet (400 m) below sea level, and whose deepest point is another 1,300 ft lower still. Between the Sea of Galilee and the Dead Sea, the Jordan flows though a valley known as the Ghor, in which it has formed a lower flood plain, the Zor, an area of thick vegetation and probably that which is described in Jeremiah 12: 5 as the `jungle [NRSV thickets] of the Jordan'. A feature of this stretch of the river is its meandering. The distance `as the crow flies' between the Sea of Galilee and the Dead Sea is about 65 miles (105 km); but the river flows nearly 200 miles (about 320 km) to cover the distance. The most noteworthy feature of the Dead Sea is the extremely high level of saltiness of its water, some six times the salt content of the oceans, so high that no marine life can survive in it. This is due almost entirely to evaporation, since the Jordan does not wash down appreciably more chemicals than other rivers. South of the Dead Sea, the Rift Valley continues some 100 miles (160 km) until it reaches the Gulf of Aqaba. This region is known as the Arabah, although sometimes that designation is used with reference to the whole of the Rift Valley south of the Sea of Galilee.