Monthly Archives: August 2015

How we know what lies at Earth’s core

Humans have been all over the Earth. We’ve conquered the
lands, flown through the air and dived to the deepest trenches in the ocean.
We’ve even been to the Moon. But we’ve never been to the planet’s core.

We haven’t even come close. The central point of the Earth
is over 6,000km down, and even the outermost part of the core is nearly 3,000
km below our feet. The deepest hole we’ve ever created on the surface is the
Kola Superdeep Borehole in Russia, and it only goes down a pitiful 12.3 km.

All the familiar events on Earth also happen close to the
surface. The lava that spews from volcanoes first melts just a few hundred
kilometres down. Even diamonds, which need extreme heat and pressure to form,
originate in rocks less than 500km deep.

What’s down below all that is shrouded in mystery. It seems
unfathomable. And yet, we know a surprising amount about the core. We even have
some idea about how it formed billions of years ago – all without a single
physical sample. This is how the core was revealed.

One good way to start is to think about the mass of the
Earth, says Simon Redfern of the University of Cambridge in the UK.

We can estimate Earth’s mass by observing the effect of the
planet’s gravity on objects at the surface. It turns out that the mass of the
Earth is 5.9 sextillion tonnes: that’s 59 followed by 20 zeroes.

There’s no sign of anything that massive at the surface.

“The density of the material at the Earth’s surface is
much lower than the 
average density of the whole Earth, so that tells us
there’s something much denser,” says Redfern. “That’s the first
thing.”

Essentially, most of the Earth’s mass must be located
towards the centre of the planet. The next step is to ask which heavy materials
make up the core.

The answer here is that it’s almost certainly made mostly of
iron. The core is thought to be around 80% iron, though the exact figure is up
for debate.

The main evidence for this is the huge amount of iron in the
universe around us. It is one of the ten most common elements in our galaxy,
and is frequently found in meteorites.

Given how much there is of it, iron is much less common at
the surface of the Earth than we might expect. So the theory is that when Earth
formed 4.5 billion years ago, a lot of iron worked its way down to the core.

That’s where most of the mass is, and it’s where most of the
iron must be too. Iron is a relatively dense element under normal conditions,
and under the extreme pressure at the Earth’s core it would be crushed to an
even higher density, so an iron core would account for all that missing mass.

But wait a minute. How did that iron get down there in the
first place?
The iron must have somehow gravitated – literally – towards
the centre of the Earth. But it’s not immediately obvious how.

Most of the rest of the Earth is made up of rocks called
silicates, and molten iron struggles to travel through them. Rather like how
water on a greasy surface forms droplets, the iron clings to itself in little
reservoirs, refusing to spread out and flow.

A possible solution was discovered in 2013 by Wendy Mao of
Stanford University in California and her colleagues. They wondered what
happened when the iron and silicate were both exposed to extreme pressure, as
happens deep in the earth.

By pinching both substances extremely tightly using
diamonds, they were able to force molten iron through silicate.

“The pressure actually changes the properties of how
iron interacts with the silicate,” says Mao. “At higher pressures a
‘melt network’ is formed.”

This suggests the iron was gradually squeezed down through
the rocks of the Earth over millions of years, until it reached the core.

At this point you might be wondering how we know the size of
the core. What makes scientists think it begins 3000km down? There’s a one-word
answer: seismology.

When an earthquake happens, it sends shockwaves throughout
the planet. Seismologists record these vibrations. It’s as if we hit one side
of the planet with a gigantic hammer, and listened on the other side for the
noise.

“There was a Chilean earthquake in the 1960s that
generated a huge amount of data,” says Redfern. “All the seismic
stations dotted all over the Earth recorded the arrival of the tremors from
that earthquake.”

Depending on the route those vibrations take, they pass
through different bits of the Earth, and this affects how they
“sound” at the other end.

Early in the history of seismology, it was realised that
some vibrations were going missing. These “S-waves” were expected to
show up on one side of the Earth after originating on the other, but there was
no sign of them.

The reason for this was simple. S-waves can only reverberate
through solid material, and can’t make it through liquid.

They must have come up against something molten in the
centre of the Earth. By mapping the S-waves’ paths, it turned out that rocks
became liquid around 3000km down.

That suggested the entire core was molten. But seismology
had another surprise in store.

In the 1930s, a Danish seismologist named Inge Lehmann
noticed that another kind of waves, called P-waves, unexpectedly travelled
through the core and could be detected on the other side of the planet.

She came up with a surprising explanation: the core is
divided into two layers. The “inner” core, which begins around
5,000km down, was actually solid. It was only the “outer” core above
it that was molten.

Lehmann’s idea was eventually confirmed in 1970, when more
sensitive seismographs found that P-waves really were travelling through the
core and, in some cases, being deflected off it at angles. Sure enough, they
still ended up on the other side of the planet.

It’s not just earthquakes that sent useful shockwaves
through the Earth. In fact, seismology owes a lot of its success to the
development of nuclear weapons.

A nuclear detonation also creates waves in the ground, so
nations use seismology to listen out for weapons tests. During the Cold War
this was seen as hugely important, so seismologists like Lehmann got a lot of
encouragement.


Rival countries found out about each other’s nuclear
capabilities and along the way we learned more and more about the core of the
Earth. Seismology is still used to detect nuclear detonations today.

We can now draw a rough picture of the Earth’s structure.
There is a molten outer core, which begins roughly halfway to the planet’s
centre, and within it is the solid inner core with a diameter of 1,220 km.

But there is a lot more to try and tease out, especially
about the inner core. For starters, how hot is it?

This turns out to be quite tricky to determine, and baffled
scientists until quite recently, says Lidunka Vočadlo of University College
London in the UK. We can’t put a thermometer down there, so the only solution
is to create the correct crushing pressure in the lab.

In 2013 a team of French researchers produced the best
estimate to date. They subjected pure iron to pressures a little over half that
at the core, and extrapolated from there. They concluded that the melting point
of pure iron at core temperatures is around 6,230 °C. The presence of other
materials would bring the core’s melting point down a bit, to around 6,000 °C.
But that’s still as hot as the surface of the Sun.

A bit like a toasty jacket potato, Earth’s core has stayed
warm thanks to heat retained from the formation of the planet. It also gets
heat from friction as denser materials shift around, as well as from the decay
of radioactive elements. Still, it is cooling by about 100 °C every billion
years.

Knowing the temperature is useful, because it affects the
speed at which vibrations travel through the core. That is handy, because there
is something odd about the vibrations.

P-waves travel unexpectedly slowly as they go through the
inner core – slower than they would if it was made of pure iron.

“Wave velocities that the seismologists measure in
earthquakes and whatnot are significantly lower [than] anything that we measure
in an experiment or calculate on a computer,” says Vočadlo. “Nobody
as yet knows why that is.”

That suggests there is another material in the mix.

It could well be another metal, called nickel. But
scientists have estimated how seismic waves would travel through an iron-nickel
alloy, and it doesn’t quite fit the readings either.

Vočadlo and her colleagues are now considering whether there
might be other elements down there too, like sulphur and silicon. So far,
no-one has been able to come up with a theory for the inner core’s composition
that satisfies everyone. It’s a Cinderella problem: no shoe will quite fit.

Vočadlo is trying to simulate the materials of the inner
core on a computer. She hopes to find a combination of materials, temperatures
and pressures that would slow down the seismic waves by the right amount.

She says the secret might lie in the fact that the inner
core is nearly at its melting point. As a result, the precise properties of the
materials might be different from what they would be if they were safely solid.

That could explain why the seismic waves pass through more
slowly than expected.

“If that’s the real effect, we would be able to
reconcile the mineral physics results with the seismological results,”
says Vocadlo. “People have not been able to do that yet.”

There are plenty of riddles about the earth’s core still to
solve. But without ever digging to those impossible depths, scientists have
figured out a great deal about what is happening thousands of kilometres
beneath us.

Those hidden processes in the depths of the Earth are
crucial to our daily lives, in a way many of us don’t realise.

Earth has a powerful magnetic field, and that is all thanks
to the partially molten core. The constant movement of molten iron creates an electrical
current inside the planet, and that in turn generates a magnetic field that
reaches far out into space.

The magnetic field helps to shield us from harmful solar
radiation. If the core of the Earth wasn’t the way it is, there would be no
magnetic field, and we would have all sorts of problems to contend with.

None of us will ever set eyes on the core, but it’s good to
know it’s there.

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Paleobotanist identifies what could be the mythical ‘first flower’

Indiana University paleobotanist David Dilcher and
colleagues in Europe have identified a 125 million- to 130 million-year-old
freshwater plant as one of earliest flowering plants on Earth.

The finding, reported Aug. 17 in the Proceedings of the
National Academy of Sciences, represents a major change in the presumed form of
one of the planet’s earliest flowers, known as angiosperms.

“This discovery raises significant questions about the
early evolutionary history of flowering plants, as well as the role of these
plants in the evolution of other plant and animal life,” said Dilcher, an
emeritus professor in the IU Bloomington College of Arts and Sciences’
Department of Geological Sciences.

The aquatic plant, Montsechia vidalii, once grew abundantly
in freshwater lakes in what are now mountainous regions in Spain. Fossils of
the plant were first discovered more than 100 years ago in the limestone
deposits of the Iberian Range in central Spain and in the Montsec Range of the
Pyrenees, near the country’s border with France.

A large intact specimen of the fossil, Montsechia.Credit: David Dilcher 
Also previously proposed as one of the earliest flowers is
Archaefructus sinensis, an aquatic plant found in China.

“A ‘first flower’ is technically a myth, like the
‘first human,'” said Dilcher, an internationally recognized expert on angiosperm
anatomy and morphology who has studied the rise and spread of flowering plants
for decades. “But based on this new analysis, we know now that Montsechia
is contemporaneous, if not more ancient, than Archaefructus.”

He also asserted that the fossils used in the study were
“poorly understood and even misinterpreted” during previous analyses.

“The reinterpretation of these fossils provides a
fascinating new perspective on a major mystery in plant biology,” said
Donald H. Les, a professor of ecology and evolutionary biology at the
University of Connecticut, who is the author of a commentary on the discovery
in the journal PNAS. “David’s work is truly an important contribution to
the continued quest to unravel the evolutionary and ecological events that
accompanied the rise of flowering plants to global prominence.”

The conclusions are based upon careful analyses of more than
1,000 fossilized remains of Montsechia, whose stems and leaf structures were
coaxed from stone by applying hydrochloric acid on a drop-by-drop basis. The
plant’s cuticles – the protective film covering the leaves that reveals their
shape – were also carefully bleached using a mixture of nitric acid and
potassium chlorate.

Examination of the specimens was conducted under a stereomicroscope,
light microscope and scanning electron microscope.

The age of the plant at 125 million to 130 million years is
based upon comparisons to other fossils in the same area, notably the
freshwater algae charophytes, which places Montsechia in the Barremian age of
the early Cretaceous period, making this flowering plant a contemporary of
dinosaurs such as the brachiosaurus and iguanodon.

The precise, painstaking analysis of fossilized structures
remains crucial to paleobotany, in contrast to other biological fields, due to
the current inability to know the molecular characters of ancient plants from
millions of years ago, Dilcher said.

This careful examination was particularly important to
Montsechia since most modern observers might not even recognize the fossil as a
flowering plant.

“Montsechia possesses no obvious ‘flower parts,’ such
as petals or nectar-producing structures for attracting insects, and lives out
its entire life cycle under water,” he said. “The fruit contains a
single seed” — the defining characteristic of an angiosperm —
“which is borne upside down.”

In terms of appearance, Dilcher said, Montsechia resembles
its most modern descendent, identified in the study as Ceratophyllum. Also
known as coontails or hornworts, Ceratophyllum is a dark green aquatic plant
whose coarse, tufty leaves make it a popular decoration in modern aquariums and
koi ponds.

Next up, Dilcher and colleagues want to understand more
about the species connecting Montsechia and Ceratophyllum, as well as delve
deeper into when precisely other species of angiosperms branched off from their
ancient forefathers.

“There’s still much to be discovered about how a few
early species of seed-bearing plants eventually gave rise to the enormous, and
beautiful, variety of flowers that now populate nearly every environment on
Earth,” he said.

Story Source:
The above post is reprinted from materials provided by Indiana
University. Note: Materials may be edited for content and length.

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On this day in history – the first antiseptic operation was performed

In 1865, Dr. Joseph Lister became the first surgeon to perform
an antiseptic operation by liberal use of carbolic acid (phenol) as a
disinfectant. He had studied Louis Pasteur’s germ theory of disease, that infections
are caused by bacteria.

Lister knew carbolic acid had been effective in municipal
use for treating sewage, and decided to try using it to kill germs that would
otherwise infect wounds. He poured it on bandages, ligatures, instruments and
directly on the wound and hands.

His first patient to benefit from this procedure was James
Greenlees, age 12, whose broken leg was treated after being run over by a cart.
The dressing was soaked with carbolic acid and linseed oil. The wound healed
without infection. Lister continued his protocol of hygiene, and reduced the
surgical death rate from 45% to 15%.

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Volcanic rocks resembling Roman concrete explain record uplift in Italian caldera

The discovery of a fiber-reinforced, concrete-like rock
formed in the depths of a dormant supervolcano could help explain the unusual
ground swelling that led to the evacuation of an Italian port city and inspire
durable building materials in the future, Stanford scientists say.

The “natural concrete” at the Campi Flegrei
volcano is similar to Roman concrete, a legendary compound invented by the
Romans and used to construct the Pantheon, the Coliseum, and ancient shipping
ports throughout the Mediterranean.

“This implies the existence of a natural process in the
subsurface of Campi Flegrei that is similar to the one that is used to produce
concrete,” said Tiziana Vanorio, an experimental geophysicist at
Stanford’s School of Earth, Energy & Environmental Sciences.

Campi Flegrei lies at the center of a large depression, or
caldera, that is pockmarked by craters formed during past eruptions, the last
of which occurred nearly 500 years ago. Nestled within this caldera is the
colorful port city of Pozzuoli, which was founded in 600 B.C. by the Greeks and
called “Puteoli” by the Romans.

Beginning in 1982, the ground beneath Pozzuoli began rising
at an alarming rate. Within a two-year span, the uplift exceeded six feet-an
amount unprecedented anywhere in the world. “The rising sea bottom
rendered the Bay of Pozzuoli too shallow for large craft,” Vanorio said.

Making matters worse, the ground swelling was accompanied by
swarms of micro-earthquakes. Many of the tremors were too small to be felt, but
when a magnitude 4 quake juddered Pozzuoli, officials evacuated the city’s
historic downtown. Pozzuoli became a ghost town overnight.

A teenager at the time, Vanorio was among the approximately
40,000 residents forced to flee Pozzuoli and settle in towns scattered between
Naples and Rome. The event made an impression on the young Vanorio, and inspired
her interests in the geosciences. Now an assistant professor at Stanford,
Vanorio decided to apply her knowledge about how rocks in the deep Earth
respond to mechanical and chemical changes to investigate how the ground
beneath Pozzuoli was able to withstand so much warping before cracking and
setting off micro-earthquakes.

“Ground swelling occurs at other calderas such as
Yellowstone or Long Valley in the United States, but never to this degree, and
it usually requires far less uplift to trigger earthquakes at other
places,” Vanorio said. “At Campi Flegrei, the micro-earthquakes were
delayed by months despite really large ground deformations.”

To understand why the surface of the caldera was able to
accommodate incredible strain without suddenly cracking, Vanorio and a
post-doctoral associate, Waruntorn Kanitpanyacharoen, studied rock cores from
the region. In the early 1980s, a deep drilling program probed the active
geothermal system of Campi Flegrei to a depth of about 2 miles. When the pair
analyzed the rock samples, they discovered that Campi Flegrei’s caprock-a hard
rock layer located near the caldera’s surface-is rich in pozzolana, or volcanic
ash from the region.

The scientists also noticed that the caprock contained
tobermorite and ettringite-fibrous minerals that are also found in humanmade
concrete. These minerals would have made Campi Flegrei’s caprock more ductile,
and their presence explains why the ground beneath Pozzuoli was able to
withstand significant bending before breaking and shearing. But how did
tobermorite and ettringite come to form in the caprock?

Once again, the drill cores provided the crucial clue. The
samples showed that the deep basement of the caldera-the “wall” of
the bowl-like depression-consisted of carbonate-bearing rocks similar to
limestone, and that interspersed within the carbonate rocks was a needle-shaped
mineral called actinolite.

“The actinolite was the key to understanding all of the
other chemical reactions that had to take place to form the natural cement at
Campi Flegrei,” said Kanitpanyacharoen, who is now at Chulalongkorn
University in Thailand.

From the actinolite and graphite, the scientists deduced
that a chemical reaction called decarbonation was occurring beneath Campi
Flegrei. They believe that the combination of heat and circulating mineral-rich
waters decarbonates the deep basement, prompting the formation of actinolite as
well as carbon dioxide gas. 

As the CO2 mixes with calcium-carbonate and
hydrogen in the basement rocks, it triggers a chemical cascade that produces
several compounds, one of which is calcium hydroxide. Calcium hydroxide, also
known as portlandite or hydrated lime, is one of the two key ingredients in
humanmade concrete, including Roman concrete. Circulating geothermal fluids transport
this naturally occurring lime up to shallower depths, where it combines with
the pozzolana ash in the caprock to form an impenetrable, concrete-like rock
capable of withstanding very strong forces.

“This is the same chemical reaction that the ancient
Romans unwittingly exploited to create their famous concrete, but in Campi
Flegrei it happens naturally,” Vanorio said.

In fact, Vanorio suspects that the inspiration for Roman
concrete came from observing interactions between the volcanic ash at Pozzuoli
and seawater in the region. The Roman philosopher Seneca, for example, noted
that the “dust at Puteoli becomes stone if it touches water.”

“The Romans were keen observers of the natural world
and fine empiricists,” Vanorio said. “Seneca, and before him
Vitruvius, understood that there was something special about the ash at
Pozzuoli, and the Romans used the pozzolana to create their own concrete,
albeit with a different source of lime.”

Pozzuoli was the main commercial and military port for the
Roman Empire, and 
it was common for ships to use pozzolana as ballast while
trading grain from the eastern Mediterranean. As a result of this practice,
volcanic ash from Campi Flegrei-and the use of Roman concrete-spread across the
ancient world. Archeologists have recently found that piers in Alexandria,
Caesarea, and Cyprus are all made from Roman concrete and have pozzolana as a
primary ingredient.

Interestingly, the same chemical reaction that is
responsible for the unique properties of the Campi Flegrei’s caprock can also
trigger its downfall. If too much decarbonation occurs-as might happen if a
large amount of saltwater, or brine, gets injected into the system-an excess of
carbon dioxide, methane and steam is produced. As these gases rise toward the
surface, they bump up against the natural cement layer, warping the caprock.
This is what lifted Pozzuoli in the 1980s. When strain from the pressure
buildup exceeded the strength of the caprock, the rock sheared and cracked,
setting off swarms of micro-earthquakes. As pent-up gases and fluids vent into
the atmosphere, the ground swelling subsided. Vanorio and Kanitpanyacharoen
suspect that as more calcium hydroxide was produced at depth and transported to
the surface, the damaged caprock was slowly repaired, its cracks
“healed” as more natural cement was produced.

Vanorio believes the conditions and processes responsible
for the exceptional rock properties at Campi Flegrei could be present at other
calderas around the world. A better understanding of the conditions and
processes that formed Campi Flegrei’s caprock could also allow scientists to
recreate it in the lab, and perhaps even improve upon it to engineer more
durable and resilient concretes that are better able to withstand large
stresses and shaking, or to heal themselves after damage.

“There is a need for eco-friendly materials and
concretes that can accommodate stresses more easily,” Vanorio said.
“For example, extracting natural gas by hydraulic fracturing can cause
rapid stress changes that cause concrete well casings to fail and lead to gas leaks
and water contamination.”

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