Stories tagged Earth Structure and Processes

Aug
28
2007

How old is the earth?

Oldest diamond puzzles scientists
Oldest diamond puzzles scientists
Scientists mostly agree that the Earth is about 4.54 billion years old (USGS.gov). This age represents a compromise between the interpretations of oldest-known terrestrial minerals – small crystals of zircon from the Jack Hills of Western Australia – and astronomers' and planetologists' determinations of the age of the solar system based in part on radiometric age dating of meteorite material and lunar samples. (Read why meteorites were used here.)

How fast did Earth cool?

Earth's beginning is known as the Hadean—because geologists speculate the planet's surface boiled and bubbled with molten lava under a steady bombardment of comets and meteorites. Diamonds would never form in such conditions yet diamonds over 4.2 billion years old have now been found. Does this mean that the Earth cooled enough that a cool crust and maybe even oceans existed 4.25 billion years ago?

Oldest diamonds within zircon may give the answers.

Because no rocks older than 4 billion years had previously been found, the Hadean period of Earth was thought to be at least 500 million years. Zircons found in Jack Hills Austalia changed this thinking.
When a zircon forms from a solidifying magma, atoms of zirconium, silicon and oxygen combine in exact proportions (ZrSiO4) to create a crystal structure unique to zircon; uranium occasionally substitutes as a trace impurity. Atoms of lead, on the other hand, are too large to comfortably replace any of the elements in the lattice, so zircons start out virtually lead-free. The uranium-lead clock starts ticking as soon as the zircon crystallizes. Thus, the ratio of lead to uranium increases with the age of the crystal. Scientists can reliably determine the age of an undamaged zircon within 1 percent accuracy, which for the early earth is about plus or minus 40 million years.
Furthermore, the ratios of radioactive isotopes of neodymium and hafnium--two elements used to determine the timing of continental-crust-forming events--suggest that significant amounts of continental crust formed as early as 4.4 billion years ago.Scientific American

Explainations for the diamonds are uncertain.

Craig O'Neill, a geochemist with Sydney's Macquarie University, at first thought the diamonds were due to heavy meteroite bombardment, forming in large impact craters due to the huge pressures reached. Dr Nemchin agreed that the birth of the diamonds was key, although he speculated that they formed when new-formed hunks of the Earth's crust collided. Study co-author Wilde said, "The bottom line is that we really honestly don't know why they're (the diamonds) there." The 4.25-billion-year-old diamonds "suggest the additional possibility that the diamonds have formed by some process that is not yet understood." He suggests the researchers should test the diamonds' carbon isotopic composition and whether nitrogen is present as single or paired atoms. This would indicate the time spent in the mantle and whether it was under relatively high or low temperatures.
Dr Nemchin says analysis of the carbon isotopes would be the next obvious step and could provide clues about the possible existence of life forms 4.2 billion years ago.

Sources:

The study, led by Martina Menneken, a master's student at the Westfaelische Wilhelms-Universitaet, appeared in the Aug. 23, 2007 journal, Nature. Alexander Nemchin from Curtin University of Technology also contributed.
I also recommend the Scientific American article, "A cool early earth?" (October, 2005). I now have a better understanding of how diamonds and zirconium crystals can tell us about what the Earth was like more than 4 billion years ago.

Jul
07
2007

The Earth as it actually is: Here we see a revised map of the planet earth.    (Image by FuLL MoON on Flickr.com)
The Earth as it actually is: Here we see a revised map of the planet earth. (Image by FuLL MoON on Flickr.com)
Well… Maybe the home planet isn’t shrinking, exactly, but it’s slightly smaller than we used to think. So it’s kind of like it’s shrinking in our heads, which is just as bad, according to The Matrix.

Using a procedure called “Very Long Baseline Interferometry,” or just VBLI, scientists have been able to reevaluate previous estimates on the earth’s exact size. VBLI works by using a network of over 70 radio telescopes around the world to measure radio waves emitted by sources deep in space, like Quasars. Because each telescope is always going to be slightly closer or further away from the source of the radio waves, the signals are received with a slight time lag from telescope to telescope. By measuring that lag, scientists can tell the exact distances from each telescope to the Quasar, and then the distances between two telescopes “to the preciseness of two millimeters per 1,000 kilometers.” Through all this, they have discovered that the Earth is just slightly smaller than we used to think - just a matter of millimeters, though.

But what does a matter of millimeters mean on a global scale? The implications, I think, will startle you. For instance, the state of Rhode Island no longer exists. And Delaware is just a beach now. My bedroom, formerly a palatial 12’ by 13’ 6” is now a claustrophobic 11’ 11” by 13’ 5.9”. I had to throw some books out. It’s a scary world we live in, so dominated by concepts.

The Geodesists who have developed this world-measuring process are hopeful, however, that it will have the potential to make up for its grim introduction. By measuring the Earth’s size so exactly, VLBI will allow us to measure minute changes in sea level and track the progression of global warming, or to follow the exact movement of the tectonic plates (It turns out that the Swiss and us are moving 18 millimeters away from each other every year. I’m not sure how I feel about this.)

The March of VLBI

Nov
17
2006

Noah's Ark: by Edward Hicks
Noah's Ark: by Edward Hicks

Mega-tsunami

What happens when a giant meteor lands in the ocean? Not only would there be a big splash, but heat and energy equal to a multi-megaton bomb would melt rock, generate steam and wind, and create a mega-tsunami. The mega-tsunami would be at least 600 feet high. Such a wave would carry ocean sediments several miles inland creating formations called chevrons.

Google maps reveal new craters

Using google-maps scientists are finding many such chevrons. Two chevrons found over four miles inland near Carpentaria in north central Australia both pointed north into the ocean. Using surface altimetry data from satellites, two craters were found on the ocean bottom that contained melted rocks and magnetic spheres with fractures and textures characteristic of a cosmic impact.

“We found diatoms fused to tektites,” a glassy substance formed by meteors. The molten glass and shattered rocks could not be produced by anything other than an impact."

New evidence indicates meteor strike around time of Noah

Last August scientists collected samples from four huge chevrons in Madegascar.

Last month, Dee Breger, director of microscopy at Drexel University in Philadelphia, looked at the samples under a scanning electron microscope and found benthic foraminifera, tiny fossils from the ocean floor, sprinkled throughout. Her close-ups revealed splashes of iron, nickel and chrome fused to the fossils.
About 900 miles southeast from the Madagascar chevrons, in deep ocean, is Burckle crater, which Dr. Abbott discovered last year. Although its sediments have not been directly sampled, cores from the area contain high levels of nickel and magnetic components associated with impact ejecta.
Burckle crater has not been dated, but Dr. Abbott estimates that it is 4,500 to 5,000 years old.

Mythology dates flood to Solar eclipse in 2807 B.C.

An environmental archaeologist, Dr. Masse, at the Los Alamos National Laboratory in New Mexico analyzed 175 flood myths from around the world, and tried to relate them to known and accurately dated natural events like solar eclipses and volcanic eruptions. Fourteen flood myths specifically mention a full solar eclipse, which could have been the one that occurred in May 2807 B.C.
Half the myths talk of a torrential downpour. A third talks of a tsunami. Worldwide they describe hurricane force winds and darkness during the storm. All of these could come from a metior strike and mega-tsunami.

Source article from New York Times.

Oct
09
2006

Spaceship Earth: Amazon.com image
Spaceship Earth: Amazon.com image

Captain, we are running low on supplies.

R. Buckminster Fuller's 1969 book imagines humanity as a crew aboard a tiny spaceship traveling through infinity. We have limited water, food, and fuel. Because of our proximity to the sun, we are given a limited budget of additional fuel which allows growth of food, trees, and fish. The sun's energy input also cycles our water and air. We even have past energy from the sun stored up in the form of coal and oil.

What is biocapacity?

What happens if we use up more food and energy each year than the Earth/Sun system can regenerate? Each year Global Footprint Network calculates humanity’s Ecological Footprint (its demand on cropland, pasture, forests and fisheries) and compares it with global biocapacity (the ability of these ecosystems to generate resources and absorb wastes). They declared that today (Oct. 9th) is Global Overshoot Day, the day we passed our biocapacity limit.

"We are clearly drawing natural capital ... the point about collapse is that we don't know when some of the systems in the global atmosphere and fish will collapse but we do know that collapse is a very real possibility" says Professor Tim Jackson, head of sustainable development at Surrey University via The Independent)

We are living beyond our means. Earth's six billion inhabitants and their rising living standards are putting an intolerable strain on nature.

Overfishing, deforestation, overpopulation, etc.

The biggest problem relating to the over-consumption of resources is climate change, but its other effects include deforestation, falling agricultural yields and overfishing.
Overfishing should be easy to understand. If you harvest fish with nets faster than they can reproduce, pretty soon there are not enough fish. Remember what happened at Red Lake.

Global Footprint Network's vision

Global Footprint Network is committed to fostering a world where all people have the opportunity to live satisfying lives within the means of Earth's ecological capacity. You can read about their accomplishments and publications here.

Sep
28
2006

Cave Exploration: Timpanogos Cave photo by Art Oglesby
Cave Exploration: Timpanogos Cave photo by Art Oglesby

Beautiful cave found in California

Four amateur cave explorers from the nonprofit Cave Research Foundation discovered a "jaw dropping...beautiful" cave in the Sequoia National Park, California. The cave, named Ursa Minor, has been called one of the most significant finds in a generation.
Scott McBride, an explorer from San Andreas (Calaveras County) who has discovered 50 caves since 1994, first spotted an opening about the size of a baseball.

The four explorers have joined Joel Despain (the parks' cave manager) and other geologists in mapping the cave, but they haven't found the end. The cave features five rooms -- the biggest is about 200 feet wide and 50 feet tall -- and at least five leads, or passages, leading farther underground. San Francisco Chronicle

I found their account of entering this new cave particularly interesting because I just toured three caves during my recent road trip to California. My wife, Ann, and I toured Wind Cave in South Dakota, Timpanogos Cave in Utah (where my wife was a tour guide 30 years ago), and Lehman Cave in Nevada.

Caves need to be protected

These caves are national treasures and are now protected. I was shocked to learn that early visitors were allowed to break off pieces of the cave as a souvenir. In the early 1900's groups could even rent out the cave for overnight parties and lit campfires for heat and light.
This newest cave named Ursa Minor for its thousands of star like sparkles and a bear skeleton within may never be opened to the public.

The cave is littered with animal skeletons and teems with spiders, centipedes, millipedes and other invertebrates. Experts believe Ursa Minor will feature unique species found nowhere else, adding to the 27 never-before-seen species discovered during a recent study of invertebrates in the park's 239 other caves.

For now, the top priority is thoroughly mapping the cave and installing a gate at its mouth to keep sightseers and vandals at bay. No more than a few dozen people will ever see Ursa Minor, and those who have said they'll never forget it.

Jun
04
2006


Meteor Crater near Winslow, AZ: This crater formed when a meteor collided with Earth about 50,000 years ago. It is approximately 3/4 mile in diameter and 650 feet deep.
Courtesy Mark Ryan

A 300 mile wide crater (bigger than Ohio) has been detected beneath a half-mile of ice in Anartica. This crater is twice as big as the one thought to have killed the dinosaurs. Reseachers believe the impact may have broken up the Gondwana supercontinent, pushing what is now Australia northward.

Two separate data sets were combined to understand more about this impact. Radar to detect a crater, and gravity measurements to detect a mass concentration, or "mascon" in the same place. When a large mass slams into the earth, there is a rebound of mantle material up into the earth's crust creating a bump or mascon..

"On the moon, you can look at craters, and the mascons are still there," von Frese said. "But on Earth, it's unusual to find mascons, because the planet is geologically active. The interior eventually recovers and the mascon goes away." He cited the very large and much older Vredefort crater in South Africa that must have once had a mascon, but no evidence of it can be seen now.
"Based on what we know about the geologic history of the region, this Wilkes Land mascon formed recently by geologic standards -- probably about 250 million years ago," he said. "In another half a billion years, the Wilkes Land mascon will probably disappear, too." Ralph von Frese, a professor of geological sciences at Ohio State University

The Permian-Triassic extinction about 250 million years ago, when almost all animal life on Earth died out, may have resulted from this impact.

Not all scientists agree, however

Scientists contacted by news@nature.com say they are sceptical, as no signs of such an enormous impact have been found in other, well-studied areas of Antarctica. Jane Francis, a geologist at the University of Leeds says, "That sequence has been worked on before, and no one has found evidence to support a massive impact like this," Paul Wignall, a palaeontologist at the University of Leeds, UK, who studies mass-extinction events says that few scientists will be convinced by the hypothesis until the team can precisely date their crater directly, and find rocks there that have been altered by the searing heat of the explosion.

Most think that the extinction started when a vast volcanic eruption released huge amounts of gas, including sulphur dioxide and carbon dioxide, into the atmosphere, causing acid rain and greenhouse warming. Von Frese notes that the explanations aren't mutually exclusive: the shockwaves from a huge impact could have travelled through the planet to trigger the eruptions in Siberia, delivering a devastating combination of disasters.

Too much ice covers the putative crater for a drilling expedition. But Von Frese hopes to make a research trip to Antarctica to look for rocks at the base of the ice sheet along the continent's coast that could attest to an impact.

Sources:
NatureNews
physorg
space
BBCnews
Yahoo news

Apr
24
2006


JOIDES Resolution: Courtesy Ocean Drilling Program

About 500 miles west of Costa Rica, scientists dug deep (and I mean DEEP) into the Earth’s crust. For the first time, layers of pristine igneous rock were retrieved. Their findings included a dark rock called gabbro. Gabbro is an igneous rock formed when molten magma is trapped underneath the Earth’s surface, cools and forms a crystalline mass.

JOIDES Resolution, the drill ship, bored nearly a mile into our planet’s oceanic crust recovering a complete stratified core of the overlaying crust in the Pacific Ocean. Studying gabbro along with crust sections will better inform scientists about the processes pertaining to crust formation and structure, plate tectonics, mountain formation as well as earthquake and volcano triggers.

Douglas Wilson, study co-author from the University of California, Santa Barbara, told LiveScience “This process covers 60 percent of the Earth’s surface, and it’s an ongoing process that has replaced all of the seafloor since 180 million years ago. In terms of understanding the planet, it’s a fundamental process."

Oct
13
2005

Scientists at Rutgers University in New Jersey have discovered that the amount of oxygen in the Earth's atmosphere has more than doubled over the last 205 million years.

By studying samples of seafloor material going back millions of years, they determined that the atmosphere was only 10% oxygen during the time of the dinosaurs. It rose as high as 23% by 40 million years ago. (The air is 21% oxygen today.) That's about the time that really large mammals, like elephants and rhinos, started to emerge.

Oxygen levels may have affected the evolution of mammals. These warm-blooded creatures need three to six times as much oxygen as a reptile of the same size. The lack of oxygen may have prevented them from growing very large. But as oxygen levels increased, mammals could start getting bigger.

Oct
09
2005

There was a 7.7 magnitude earthquake centered in Pakistan on October 8th, 2005 at 8:50am Pakistan time (that's 10:50pm on Friday in Minnesota). The earthquake devastated the region, leaving many villages destroyed and killing thousands in Pakistan and India. It is one of the strongest earthquakes to hit this area in living memory. Pakistan's president Pervez Musharraf described the disaster as the country's "worst-ever."

A clash of titans

The earth's continents rest upon large plates of rock that are slowly moving around the surface of the earth. For millions of years, the Indian subcontinent has been slowly moving north towards Europe and Asia (Eurasia). About 40-50 million years ago (mya), India slammed into Eurasia. Because both India and Eurasia were continents the Eurasia crust crumpled upwards, creating the Himalayan mountains. The leading edge of India was eventually forced underneath the continent in a process geologists call subduction. This movement is still happening today. However, as India continues to move slowly north, it gets hung up and energy builds. When enough energy builds up, there are short bursts of movement, releasing this massive energy and shaking and buckling the ground in what we call an earthquake.

Past disasters

In the last hundred years, several other earthquakes of similar strength have struck this region:

  • 2001 - 11,500 people killed - 7.6 magnitude quake struck Indian city of Gujarat
  • 1991 - 700 people killed - 6.7 magnitude quake struck in the remote Hindukush mountains of Afghanistan
  • 1935 - 35,000 people killed - 7.6 magnitude quake struck Quetta in the Baluchistan province (now western Pakistan)
  • 1905 - 20,000 people killed - 7.9 magnitude quake struck Kangra, in northern India