Plate Tectonics Earlier Than Thought

via Astrobiology, news of research into Earth's ancient past appears to indicate the presence of water and the geophysics of the plate tectonic system far earlier than previous estimates. New analysis by UCLA geochemists of extremely early forming zircon chrystals found in ancient magma fields show that the chrystals formed at a much lower temperature than can be explained without the presence of water. Furthermore, the evidence seems to indicate that the crystals could not have formed anywhere but in a subduction zone, where colliding tectonic seafloor plates move underneath the continental plates.

"We are proposing that there was plate-tectonic activity in the first 500 million years of Earth's history," said geochemistry professor Mark Harrison, director of UCLA's Institute of Geophysics and Planetary Physics and co-author of the Nature paper. "We are reporting the first evidence of this phenomenon."

"Unlike the longstanding myth of a hellish, dry, desolate early Earth with no continents, it looks like as soon as the Earth formed, it fell into the same dynamic regime that continues today," Harrison said. "Plate tectonics was inevitable, life was inevitable. In the early Earth, there appear to have been oceans; there could have been life — completely contradictory to the cartoonish story we had been telling ourselves."

The crystal analysis was done by an ion microprobe, which shoots beams of ions into a substance to determine its precise chemical composition by means of a mass spectrometer. The analysis of the zircon samples found in Western Australia showed ages exceeding 4 billion years. The accepted theories of plate tectonics had the system starting much more recently, no more than 3.5 billion years ago. The Earth is thought to have formed around 4.5 billion years from today.

Ice Remained Even During Warmest Epoch

Livescience notes that even during the warmest period we can determine while life lived on Earth, during the Cretaceous Thermal Maximum 91 million years ago there was still an ice cap at the South Pole. During this period the temperature in tropical seas was up to 12 degrees Fahrenheit warmer than today. While there was still ice in the deep south, the northern arctic latitides were the home of heat loving crocodiles.

The Unique Earth

Nice article at FoxNews (apparently linked in from Space.com) about the many unique and interrelated features of our shiny blue marble. First up is the location - at just the right orbit around our sun for the temperature to allow liquid water to form.

"It has liquid water, plate tectonics and an atmosphere that shelters it from the worst of the sun's rays. But many scientists agree our planet's most special feature might just be us. "It's the only planet we know of that has life," said Alan Boss, a planet formation theorist at the Carnegie Institution of Washington in Washington, D.C."

Liquid water allows for plate tectonics, the movement of the planet's land masses which allows for the carbon-silicate cycle (where the seafloor recycles carbon by subducting under the land masses) all of which also helps regulate the planet's temperature to keep the water largely in a liquid state. Plate tectonics may also help drive the rotation of the Earth's core, generating the magnetic field that protects the Earth and its atmosphere from the solar wind and high energy particles.

"Plate tectonics and water are inextricably linked. Not only does plate tectonics enable liquid water to exist by way of regulating the temperature, but many scientists have argued water enables plate tectonics to happen. "Without water the planet would be geologically dead," said Caltech's Mike Brown, discoverer of the newly reclassified "plutoid" object named Eris, which lies beyond Pluto in our solar system. "Water is what lubricates plate tectonics, which is what leads to the extreme difference between continents and seafloors, the large amount of earthquakes and volcanoes, fresh mountain-building. Venus has no water, no plate tectonics, no deep sea floor, no steep mountains, no continents, probably few earthquakes or volcanoes. A much less geologically interesting place!"

Another aspect is the Earth's size - large enough to hold an atmosphere, yet small enough to remain rocky and not grow into a gas giant. There is also the factor of the Moon, which drives the Earth's ocean tides and stabilizes the Earth's rotation, preventing the poles from wandering erratically, which could lead to massive climate shifts and prevent life from evolving. These tides may also have helped life along by giving an assist to life capable of living on land, which is the really the most unique aspect of our planet - life itself, and (so-called) intelligent life to boot. The examination of the Martian soils currently underway and future research on moons such as Titan and Europa are not likely to change this primary characteristic of Earth.

Earth's Gooey Internal Structure

Livescience editor Rob Roy Britt examines some of the new findings & new ideas on the Earth's internal composition, being releases in Science magazine. The old core, mantle and crust structure theory has been shown to be a tad simplistic.

The crust extends from the surface to a depth of about 25 miles surrounding the mantle, an area of hot silicate rock, now divided into the upper and lower mantles, extending to a depth of around 1800 miles. Deeper yet is the nickel-iron core, which can also be further discriminated into an outer and inner core region. Some of the new analysis shows the mantle is composed of slightly different material than initially believed, with two large 'blobs' of chemically distinct materials on each side of the planet, one under the Pacific and the other under the Atlantic and Africa. An ASU researcher describes it this way:

"Imagine a pot of water boiling," explains researcher Allen McNamara of Arizona State University. "That would be all one kind of composition. Now dump a jar of honey into that pot of water. The honey would be convecting on its own inside the water and that's a much more complicated system."

The new theories regarding the Earth's interior composition help explain the quite curious way seismic waves travel through the Earth when an event occurs, with the waves making unexplained speed changes as they travel throught the planet.

Earth's Unbalance Sent Continents Wandering

Some interesting developments in the world of geoscience reported by NG. Some new evidence of switches in Earth's magnetic fields found in ancient rock samples seem to support a controversial theory regarding the speed of continental movements in Earth's plate tectonic system.

"Bernhard Steinberger and Trond Torsvik, of the Geological Survey of Norway, analyzed rock samples dating back 320 million years to hunt for clues in Earth's magnetic field about the history of plate motions. The researchers found evidence of a steady northward continental motion and, during certain time intervals, clockwise and counterclockwise rotations.
That pattern matches the predictions of a phenomenon known as true polar wander, a theory first proposed in the 1950s. The theory states that at times Earth's surface mass becomes imbalanced. The continents become dramatically offset from the planet's spin axis and so move rapidly to right themselves."

The evidence of this phenomenon is difficult to differentiate from the slower more regular continental movements, but the new analysis appears to show a dramatic shift of up to 18 degrees of latitude taking place over the last 320 million years. Earlier studies from the late 90s also seem to indicate another dramatic shift taking place around 550 million years ago, around the same time as the Cambrian Explosion, the diverse evolutionary period where a fantastic assortment of new life forms appeared.

The researchers of that period hypothesize that one of the planet's major subduction zones, where the ocean seafloor descends into the mantle under the continents, shut down as the continents formed the supercontinent Gondwanaland. The supercontinent then rotated rpaidly at a 90 degree angle and sent North America sprinting to the equator from deep in the southern hemishpere a mere 16 million years later, a relatively short span in geologic terms.

Another item of interest is that the the same theory appears to be applicable to the planet Mars, and the disappearance of what is believed to have been an ocean in the Northern hemishere as that planet's poles wandered.

Inner Planets May Have Different Origins

via National Geographic, a new analysis is challenging the long held theory that the inner rocky worlds in our solar system formed from the same general building block materials. The idea is that these planets are formed from the same mineral building blocks as the most common and oldest type of asteroids and meteorites, called chondrites. However, Earth's mineral composition doesn't quite match up, and a new French study (French?) of Mars and the Moon suggest that these worlds don't match up either.

"What our results suggest is that the sorting of the elements that make up these planets may have happened at a much earlier stage than had been believed," said Alex Halliday, a study co-author from Oxford University. "The composition of these worlds is inconsistent with them simply forming out of large 'lumps' of stony meteorites like those we see today in the asteroid belt."

Chondrites are commonly characterized by an abundance of the mineral neodymium 142, which is a byproduct of the decay of the metal samarium. However, Earth contains a higher percentage of neodynium than common chondrites, leading traditional earth science theorists to speculate that Earth's system of plate tectonics was "hiding" elements that would balance out the chemical ratio. However, the new study finds that both the Moon and Mars have the same excess of neodymium, even though they do not have active plate tectonics. These findings may suggest that the rocky planets may have formed earlier in the history of the solar system than the other chondrite type bodies.

Earth's Inner, Inner Core

Universe Today has an article stating researchers have discovered a new layer to the our shiny blue marble. The Earth's layers have been tradiitonally defined as the crust (the surface where we live), upper and inner mantle, and outer and inner core, but scientist studying the Earth's interior have discovered an inner, inner core within the center of the Earth. The rotation of Earth's iron core generates the planetary magentic field that shields us and every other living organism from stellar radiation.

University of Illinois @ Urbana-Champaign were using naturally occurring seismic sound waves to study the core, which consists of a solid inner layer and a fluid outer layer. When the examined the results form the inner core, they discovered an anomaly in the results that led to the discovery.

"The team was specifically studying how the waves were affected as they passed through the solid inner core and were surprised to see that it wasn't a uniform sphere of iron.

Instead, the seismic waves clearly showed that there's an additional layer at a diameter of 1,180 km (733 miles), which makes this less than half the diameter of the inner core. This is the Earth's inner, inner core.

So what is it? Here's what the lead scientists, Xiaodong Song had to say:

"Our results suggest the outer inner core is composed of iron crystals of a single phase with different degrees of preferred alignment along Earth’s spin axis," Sun said. "The inner inner core may be composed of a different phase of crystalline iron or have a different pattern of alignment."

Interesting, still iron but formed into a different type of structure. Still no Lost World full of dinosaurs though, sorry Jules Verne.

North Poles?

Scientific American explains that the Earth has not one North Pole, but several. While you might have heard of the difference between "true" geographic north and "magnetic" north, there are some other alternatives as well. There is also the Alaskan town named "North Pole" - and yes, they do receive quite a few cards addressed to Santa from children around Christmas time.

"Somewhat related to the geographic north pole is the considerably less famous instantaneous north pole, where Earth's rotational axis meets its surface, as well as the celestial north pole, where the axis spears the night sky (in an imaginary extension kind of way). The instantaneous north pole is not fixed. Rather, it moves in an irregular circle caused by "the Chandler wobble"—named for astronomer Seth Carlo Chandler, who discovered in 1891 that our planet wobbles as it rotates. His discovery gives rise to the "north pole of balance," which lies at the center of this circle."

While I knew about the wobble, (more correctly referred to as precession, a complete cycle of which last 26,000 years) which is the reason the star Polaris will not always be the "pole star", one thing I did not know myself regarding the magentic pole is that a compass points down at the north magentic pole but upward at the south magnetic pole, which makes a certain amount of sense. The other thing I didn't know is kind of complicated, but also pretty interesting.

"But there is another magnetically based north pole: the north geomagnetic pole. "One thing that's very confusing is the fact that there's a magnetic pole and a geomagnetic pole and that they're different," says Stefan Maus, a geomagnetic field modeler at the National Oceanic & Atmospheric Administration's (NOAA) National Geophysical Data Center. "It's a historical and slightly outdated definition."

The geomagnetic poles are almost an artifact of reducing Earth's complex and varied magnetic field to that of a simple bar magnet, or dipole. "The only thing that we really want to know is where the field is really vertical," Maus says. "This other pole, which is just an approximation, is generally not very useful and often leads to confusion." So while the north dip pole lies in Northern Canada, the northern dipole is roughly off the northwest coast of Greenland.

But the geomagnetic pole is useful, if you're in space, argues Jeffrey J. Love, a U.S. Geological Survey geophysicist. The farther away from Earth you get, the more its magnetic field actually does act like a dipole, or a bar magnet—even if in reality it is no such thing."

The complicated part of this is these dip poles/dipoles also move around, as often as every day, and this north pole is moving toward Siberia at a rate of 6 to 30 miles every year. If I count correctly there are at least six north poles, seven if you count the town, so you had better be clear what you're referring to when you refer to the North Pole. :)

Oxygen on Early Earth

Astrobiology has a good article on the substantial impact that the rise of oxygen producing organisms have had on our planet. There have been two major increases in the atmospheric oxygen levels in our distant past - both occurring between 635 and 551 million years ago.

"Today, we take oxygen for granted. But the atmosphere had almost no oxygen until 2.5 billion years ago, and it was not until about 600 million years ago when the atmospheric oxygen level rose to a fraction of modern levels. For a long time, geologists and evolutionary biologists have speculated that the rise of the breathing gas and subsequent oxygenation of the deep oceans are intimately tied to the evolution of modern biological systems."

The first change sparked a slight change in microscopic life forms, with the second having a larger impact on the evolution and diversification of early life forms, including a significant spike in complex algaes. Following these developments, the number of species nearly doubled, and shortly thereafter (in evolutionary terms, anyway) the first animals to develop external skeletal structures (shells) evolved.

Dinosaur Killer Made Quite a Splash

via ScienceDaily, a new analysis of the Chicxulub crater off Mexico's Yucatan penninsula, shows the asteroid impact that formed it 65 million years ago landed in much deeper water than previously thought. The asteroid is thought to be the major factor in the KT Extinction event which eliminated an estimated 70% of life on Earth. The amount of water vapor released into the atmosphere from the impact is now estimated to be 6 1/2 times greater than initially theorized, and that the sediments at the impact site contained far more sulfur. Sulfur released from the site would have caused an even deadlier result in two ways - by altering climate due to the cooling effect caused by sulfate aerosols and generating acid rain.

"The greater amount of water vapor and consequent potential increase in sulfate aerosols needs to be taken into account for models of extinction mechanisms," says Sean Gulick, a research scientist at the Institute for Geophysics at The University of Texas at Austin's Jackson School of Geosciences .

An increase in acid rain might help explain why reef and surface dwelling ocean creatures were affected along with large vertebrates on land and in the sea. As it fell on the water, acid rain could have turned the oceans more acidic. There is some evidence that marine organisms more resistant to a range of pH survived while those more sensitive did not.

Gulick says the mass extinction event was probably not caused by just one mechanism, but rather a combination of environmental changes acting on different time scales, in different locations. For example, many large land animals might have been baked to death within hours or days of the impact as ejected material fell from the sky, heating the atmosphere and setting off firestorms. More gradual changes in climate and acidity might have had a larger impact in the oceans."

Gulick's original intent was to determine the asteroid's trajectory, which he hoped would lead his team to the locations where the most extreme consequences of the event would be found, but instead found that the conditions at the impact site itself had more to do with the resulting extinciton event.

Hydrothermal Sea Vents Different than Theorized

A new study of the mid-ocean ridge system running throughout the Earth's oceans has given the researchers studying them a bit of a surprise. The study, the first of its kind, shows these deep ocean hydrothermal sea vents are much different than was expected.

"The hypothetical image of a hydrothermal-vent system shows water forced down by overlying pressure through large faults along ridge flanks. The water is heated by shallow volcanism, then rises toward the ridges' middles, where vents (often called "black smokers," for the cloud of chemicals they exude) tend to cluster. The new images, from a 4-kilometer-square area show a very different arrangement.

The water appears to descend instead through a sort of buried 200-meter-wide chimney atop the ridge, run below the ridge along its axis through a tunnel-like zone just above a magma chamber, and then bubble back up through a series of vents further along the ridge."

The interest in these vents comes from the fact they have an important contribution to both the study of planetary geology (they bring to the surface many interesting and valuable minerals from the Earth's interior, such as gold, as well as drive the Earth's plate tectonics system) and these vents also create areas of superheated water which have unique life forms generally classified as extremophiles, which have given us new insights into the possible areas in which life might exist on other planets.

This particular Pacific system appears to show the seawater entering into the system from a series of small cracks rather than a large fissure and that it processes much more water than believed - as much as a billion of gallons of water a year. It may also contribute insight on ocean currents, whether or not the life forms found around the vents relocate or not and how they might transport themselves, as well as how heat and chemicals are cycled throughout the deep ocean and mineral deposits form in these areas.

Plate Tectonics May Be Sporadic

via ScienceDaily, plate tectonics may not be a permanent geologic process, it might temporarily "grind to a halt" when the continents group together to form a "supercontinent" such as Pangea 350 million years ago.

"Writing in the January 4 issue of Science, Paul Silver of the Carnegie Institution's Department of Terrestrial Magnetism and former postdoctoral fellow Mark Behn (now at Woods Hole Oceanographic Institution) point out that most of today's subduction zones are located in the Pacific Ocean basin. If the Pacific basin were to close, as it is predicted to do about in 350 million years when the westward-moving Americas collide with Eurasia, then most of the planet's subduction zones would disappear with it.

This would effectively stop plate tectonics unless new subduction zones start up, but subduction initiation is poorly understood. "The collision of India and Africa with Eurasia between 30 and 50 million years ago closed an ocean basin known as Tethys," says Silver. "But no new subduction zones have initiated south of either India or Africa to compensate for the loss of subduction by this ocean closure."

If this theory proves correct, it would go a long way toward explaining why the Earth has not lost as much heat as expected given its age. When the continents form these supercontinents, subduction of the seafloor stops and heat begins to build up underneath the supercontinent, leading to massive volcanic activity explaining the far out of palce igneous rocks found in the middle of continents far from the subduction zones where they are usually found.

Geologic Impact to Early Human Evolution

Another interesting article from Livescience, this time regarding early human evolution. Geology may have been an important and overlooked factor in the development of humanity.

"It's fairly well-established that changing climate, and thus vegetation, in East Africa spurred human evolution, but there has been no agreement about what exactly caused that change, said Royhan Gani. He thinks the riddle's answer is in rocks, and how big slabs of it move — altering continents and building mountains — by a process called tectonics."

Gani believes that the tectonic uplift process that occured (and is still) in Eastern Africa 3-6 million years ago, which has caused the land in the region to dramatically elevate over this period, contributed to human development by drying up the tropical and subtropical rain forest and changing the biome to a drier savanna type environment.

This in turn forced early primate species out of the forests and out onto grasslands which sped the development of bipedalism. Around 4.1 million years ago, the early human ancestor Australopithecus anamensis, one of the first bipedal primates, developed - in almost exactly the same region and time period where the forest was thinning into savanna.

Origin of Atmospheric Oxygen Discovered

via ScienceDaily, some new evidence has been discovered from the analysis of ancient rocks regarding the origin of oxygen in the Earth's atmosphere 500 million years ago. The surprising part is that the oxygen developed extremely quickly by geologic standards - only 2 million years. Tectonic upheavals led to an increase in terrestrial weathering from the sulferous atmosphere at the time, which caused a decrease in the amount of carbon in the atmosphere, leading to the then much warmer Earth to cool globally. The carbon levels dropped from as much as 20 times greater than today, trapped in seabed sediments after the weathering process. This oxygen increase in turn led to the evolution of oxygen producing algae spreads in the oceans, further tipping the balance of gasses in the atmospheric blanket towards oxygen.

"Tectonic activity led to increased weathering, which pulled carbon dioxide from the air and cooled the climate. Then, as the oceans cooled to more hospitable temperatures, the plankton prospered -- and in turn created more oxygen through photosynthesis."

This set of conditions persisted for around 50 million years, during which time new plant and animal species flourished, but the cooling trend accelerated with new tectonic events creating the US Applachian mountain range, leading to a severe cooling trend that resulted in a ice age so extensive that it killed off nearly half of all species living on the planet at the time, around 450 million years ago.

Oldest Diamonds on Earth Discovered

And now for some science stuff, this time from Livescience.

The oldest diamonds ever discovered have been uncovered within zircon crystals in Australia's Western Desert's Jack Hills region. The analysis of these jewels, dating from over 4 billion ears ago, have led to a new theory that postulates that the Earth was subjected to far faster cooling after its formation than previously believed, with the planet's oceans and continental crust forming quite early in its history, in fact quite shortly (in geologic terms) after the impact event that is thought to have created the Earth's moon.

"The scientists, led by Martina Menneken of the Institute of Mineralogy, ran chemical analyses of the zircons, finding the ancient crystals (and thus the enclosed diamonds) were more than 4 billion years old. That's nearly a billion years older than the previous oldest-known terrestrial diamonds and suggests the diamonds were present in material that crystallized within 300 million years of the formation of Earth, the scientists say."

Plate Tectonics

Curious article on plate tectonics - apparently the Earth releases more internal heat when the crust is made up of several smaller tectonics plates than when the crust is made up of one large one, which intuitively makes sense, but hasn't been supported by any evidence up to this point.

"The reason, the authors said, is that much of the heat from the mantle escapes near the ridges between newly formed plates. Those areas are thinner and allow more heat to pass.

The smaller the plates, the greater the heat loss from the mantle on which they float, said geophysicists from the University of Southern California, Johns Hopkins University and the University of Michigan at Ann Arbor.

Several small plates have more area close to the ridge -- and allow more heat to pass -- than one large plate, explained lead author Thorsten Becker, assistant professor of earth sciences at USC."

In addition, the study found that having several smaller plates also caused a greater amount of tectonic activity (also pretty intuitive) - with more plates rubbing on one another, more events are likely to happen. However, there is one issue that can't yet be explained - at both the rate of the Earth's heat disappation previously believed to have occurred, as well as these new higher figures, the Earth would have been impossibly hot in the distant past when the planet was formed. ???

Did a Comet Strike Great Lakes in Prehistory?

via ScienceDaily, again.

A new theory has been proposed regarding the Lesser Dryas climate event occuring about 13000 years ago. The Lesser Dryas was a cooling trend that briefly interrupted the warming climatic trend that ended the last ice age about 20000 years ago (which we are still experiencing). The Lesser Dryas is held responsible for a major extinction event that occurred about the same time that eliminated a number of the large mammal species in North America.

The theory? An impact event in the area of the Great Lakes, possibly a comet, that struck the ice sheet covering the area north of the lakes in present day Canada. The evidence? A large concentration of carbon rich soils pointing to such an impact event found in over 50 Clovis culture archaeological sites throughout North America, with the highest concentrations centered in the Lakes region.

"The researchers propose that a known reversal in the world's ocean currents and associated rapid global cooling, which some scientists blame for the extinction of multiple species of animals and the end of the Clovis Period, was itself the result of a bigger event. While generally accepted theory says glacial melting from the North American interior caused the shift in currents, the new proposal points to a large extraterrestrial object exploding above or even into the Laurentide Ice Sheet north of the Great Lakes."

Interesting. The one trouble with the theory is no impact crater, but that is easily explained by the ice sheet absorbing the impact. The results of such an impact would have been pretty devastating to both animal and human populations, and might explain the concentration of late era Clovis sites in the American Southwest.

Oldest Evidence of Plate Tectonics Discovered

via ScienceDaily.

Some of the oldest rock formations on the planet, discovered in the 1960s in Greenland and dating back to 3.8 billion years ago, and long been known to contain the oldest known living organisms, have yielded new secrets. A recent new analysis of these formations show that they also contain evidence that proves conclusively that Plate tectonic processes were already acting on the Earth at that time, over a billion years earlier than previously thought. The formation was originally part of the Atlantic ocean seafloor, and shows evidence of basalt lava flows from the same mid-ocean ridge that still flows today, responsible for the volcanic activity in Iceland.

"The study focuses on an area near the southwestern coast of Greenland where there is a rare outcrop of ancient rock, called the Isua Supracrustal Belt, which have been dated at 3.8 billion years old. The Isua rocks are ophiolites, which have a green hue from the chlorite minerals within them and are found in all major mountain belts, usually located in areas associated with volcanism and plate tectonics."

The importance of the new analysis is that the same geologic processes that operate today, like seafloor spreading and ocean crust formation, have been operating since very early in Earth's history and that such formations accrete to continental landmasses. In addition, these formations are also helping to settle a scientific dispute regarding the oxygen content of ancient seawater, which appears to be very similiar or just a bit heavier than current oceans. Both the oxygen content of the oceans and the geologic processes underway at such early dates have serious implications for other scientists theorizing on the origins of life on Earth.

Beijing Anomoly

via LiveScience.

Seismologists have detected a unusual body of water deep within the earth's crust in the deep mantle near the earht's core. When seismic waves traveling through the planet due to earth movements reach East Asia, they area slow down slightly and attenuate due to the large quantity of water stored in the rock. The heart of the phenomenon is almost right underneath the city of Beijing, China, hence the name. The quantity of water found is quite substantial, the equivalent of another Arctic Ocean. 600,000 seismograms from all over the earth were analyzed in making the find.

What will they find out next?