Rivers of Life covers evolution and natural selection processes that have made life on Earth as we know it today, and also covers mass extinction events such as asteroid impacts with our planet that have drastically altered the course and progress of life.
Since the first organisms appeared on Earth approximately 3.8 billion years ago, life on the planet has had some close calls. In the last 500 million years, Earth has undergone five mass extinctions, including the event 66 million years ago that wiped out the dinosaurs. And while most scientists agree that a giant asteroid was responsible for that extinction, there’s much less consensus on what caused an even more devastating extinction, the end-Permian extinction, that occurred 252.2 million years ago, decimating 90 percent of marine and terrestrial species, from snails and small crustaceans to early forms of lizards and amphibians.
“The Great Dying,” as it’s now known, was the most severe mass extinction in Earth’s history, and is probably the closest life has come to being completely extinguished. Possible causes include immense volcanic eruptions, rapid depletion of oxygen in the oceans, and — an unlikely option — an asteroid collision.
While the causes of this global catastrophe are unknown, an MIT-led team of researchers established in that the end-Permian extinction was extremely rapid, triggering massive die-outs both in the oceans and on land in less than 20,000 years — the blink of an eye in geologic time. The MIT team also found that this time period coincides with a massive buildup of atmospheric carbon dioxide, which likely triggered the simultaneous collapse of species in the oceans and on land.
“We’ve got the extinction nailed in absolute time and duration,” says Sam Bowring, the Robert R. Shrock Professor of Earth and Planetary Sciences at MIT. “How do you kill 96 percent of everything that lived in the oceans in tens of thousands of years? It could be that an exceptional extinction requires an exceptional explanation.”
The research team at MIT has determined that the end-Permian extinction occurred over 60,000 years, give or take 48,000 years — practically instantaneous, from a geologic perspective. The new timescale is based on more precise dating techniques, and indicates that the most severe extinction in history may have happened more than 10 times faster than scientists had previously thought.
In addition to establishing the extinction’s duration, Bowring, graduate student Seth Burgess, and a colleague from the Nanjing Institute of Geology and Paleontology also found that, 10,000 years before the die-off, , the oceans experienced a pulse of light carbon, which likely reflects a massive addition of carbon dioxide to the atmosphere. This dramatic change may have led to widespread ocean acidification and increased sea temperatures by 10 degrees Celsius or more, killing the majority of sea life.
But what originally triggered the spike in carbon dioxide? The leading theory among geologists and paleontologists has to do with widespread, long-lasting volcanic eruptions from the Siberian Traps, a region of Russia whose steplike hills are a result of repeated eruptions of magma. To determine whether eruptions from the Siberian Traps triggered a massive increase in oceanic carbon dioxide, Burgess and Bowring are using similar dating techniques to establish a timescale for the Permian period’s volcanic eruptions that are estimated to have covered over five million cubic kilometers.
“It is clear that whatever triggered extinction must have acted very quickly,” says Burgess, the lead author of a paper that reports the results in this week’s Proceedings of the National Academy of Sciences, “fast enough to destabilize the biosphere before the majority of plant and animal life had time to adapt in an effort to survive.”
In 2006, Bowring and his students made a trip to Meishan, China, a region whose rock formations bear evidence of the end-Permian extinction; geochronologists and paleontologists have flocked to the area to look for clues in its layers of sedimentary rock. In particular, scientists have focused on a section of rock that is thought to delineate the end of the Permian, and the beginning of the Triassic, based on evidence such as the number of fossils found in surrounding rock layers.
Bowring sampled rocks from this area (above), as well as from nearby alternating layers of volcanic ash beds and fossil-bearing rocks. After analyzing the rocks in the lab, his team reported in 2011 that the end-Permian likely lasted less than 200,000 years. However, this timeframe still wasn’t precise enough to draw any conclusions about what caused the extinction.
Now, the team has revised its estimates using more accurate dating techniques based on a better understanding of uncertainties in timescale measurements.
With this knowledge, Bowring and his colleagues reanalyzed rock samples collected from five volcanic ash beds at the Permian-Triassic boundary. The researchers pulverized rocks and separated out tiny zircon crystals containing a mix of uranium and lead. They then isolated uranium from lead, and measured the ratios of both isotopes to determine the age of each rock sample.
From their measurements, the researchers determined a much more precise “age model” for the end-Permian extinction, which now appears to have lasted about 60,000 years — with an uncertainty of 48,000 years — and was immediately preceded by a sharp increase in carbon dioxide in the oceans.
The new timeline adds weight to the theory that the extinction was triggered by massive volcanic eruptions from the Siberian Traps that released volatile chemicals, including carbon dioxide, into the atmosphere and oceans. With such a short extinction timeline, Bowring says it is possible that a single, catastrophic pulse of magmatic activity triggered an almost instantaneous collapse of all global ecosystems.
Andrew Knoll, a professor of earth and planetary sciences at Harvard University, says the group’s refined timeline will give scientists an opportunity to test whether the timing of the Siberian Traps eruptions coincides with the extinction.
“Most mechanisms proposed to account for the observed pattern of extinction rely on rapid environmental change, so the sharp constraints on timing also serve as tests of these ideas,” Knoll says. “[This new timeline] bring us closer to the resolution of a major problem posed by the geologic record.”
To confirm whether the Siberian Traps are indeed the extinction’s smoking gun, Burgess and Bowring plan to determine an equally precise timeline for the Siberian Traps eruptions, and will compare it to the new extinction timeline to see where the two events overlap. The researchers will investigate additional areas in China to see if the duration of the extinction can be even more precisely determined.
“We’ve refined our approach, and now we have higher accuracy and precision,” Bowring says. “You can think of it as slowly spiraling in toward the truth.”
The Daily Galaxy via MIT
Image credit: With thanks to gadabimacreative
‘Cosmos: A Spacetime Odyssey’ –Episode 3 In-Depth Review
In Episode 3, The Ship of the Imagination opens in the brooding, frigid realm of the Oort Cloud, where a trillion comets wait, taking us on a hair-raising ride, following Halley’s comet through its million-year plunge towards the Sun.
Halley’s comet was spotted by the ancient Greeks, based on accounts by ancient authors. In his work Meteorology, Aristotle wrote about the event about a century after it occurred. He said that around the same time the meteorite fell, “a comet was visible in the west.” Aristotle, a student of Plato and teacher of Alexander the Great, concluded that comets were some kind of emission from Earth that rose into the sky. The heavens, he maintained, were perfect and orderly; a phenomenon as unexpected and erratic as a comet surely could not be part of the celestial vault.
According to ancient writers, a large meteorite smacked into northern Greece between 466 BC and 467 BC. The writers also described a comet in the sky at the time the meteorite fell to Earth, but this detail has received little attention, say the researchers. Halley’s Comet would have been visible for about 80 days in 466 BC, researchers write in the Journal of Cosmology. New Scientist magazine writes that, until now, the earliest probable sighting of the comet was an orbit in 240BC, an event recorded by Chinese astronomers.If the new findings are confirmed, the researchers will have pushed back the date of the first observation of Comet Halley by 226 years.
The space rock fell during daylight hours and was about the size of “a wagon load”, according to ancient sources. The object, described as having a “burnt colour”, became a tourist attraction for more than 500 years.
Astronomer Eric Hintz and philosopher Daniel Graham, both of Brigham Young University in Provo, Utah, reconstructed the likely path of Halley’s comet and calculated that Halley’s comet could have been visible for about 80 days between early June and late August in 466BC – depending on atmospheric conditions and the darkness of the sky.
“It’s tough going back that far in time. It’s not like an eclipse, which is really predictable,” co-author Eric Hintz, from Brigham Young University in Provo, Utah, told BBC News.
In the 11th Century, Halley’s Comet was depicted on the Bayeux Tapestry. The reconstruction of the comet’s path agrees with the ancient reports, which say the comet was visible for about 75 days.
The researchers point out that while the Chinese and Babylonians kept meticulous records of heavenly phenomena for centuries, the ancient Greeks did not. The Greek accounts, howevee, do provide important information, say Graham and Hintz, such as the comet’s period of visibility from Earth.
Asked whether it was possible that the meteorite fall and the pass by Halley’s Comet could be linked, Dr Hintz was doubtful. “Tt would be really neat if they were connected – if it was a piece of Halley’s that fell. My feeling is that it was just a really cool coincidence,” said Dr Hintz.
The researchers say that there remains the possibility that other ancient sightings of comets could be uncovered from Chinese and Babylonian records.
In 1910, Halleys comet’s flyby of Earth was especially close and, thanks to extensive newspaper coverage, eagerly awaited by the general public. In fact, Earth’s orbit carried it through the end of the comet’s 24-million-mile-long tail for six hours on May 19, earning the story the day’s banner headline in The New York Times.
While most reporters turned to astronomers to get the facts straight, the yellow press helped fuel the fears that the end of the world was imminent -that the comet’s tail contained poisonous cyanide gases, and there was danger of a celestial collision with Earth.
In 1910 that spectroscopic studies of comet tails conducted by Sir William Huggins revealed that among the organic molecules found in comets was the gas cyanide. As the Earth was then expected to travel through the tail of Comet Halley, speculation ran riot that people would be asphyxiated by the cyanide molecules.
Gunter Faure and Teresa Mensing note what happened in their textbook Introduction to Planetary Science: The Geological Perspective:
“During the night of May 18/19 of 1910, when the Earth passed through the tail of comet Halley, some people took precautions by sealing the chimneys, windows, and doors of their houses. Others confessed to crimes they had committed because they did not expect to survive the night, and a few panic-stricken people actually committed suicide. Enterprising merchants sold comet pills and oxygen bottles, church services were held for overflow crowds, and people in the countryside took to their storm shelters. A strangely frivolous mood caused thousands of people to gather in restaurants, coffee houses, parks, and on the rooftops of apartment buildings to await their doom in the company of fellow humans.”
But the Earth survived unscathed, passing through only a small part of the comet’s tail. A more substantial passage through a comet’s tail had also occurred in 1861 without incident
More recently, some scientists speculate that our sun may have a stealth companion that disturbs comets from the edge of the solar system — a giant planet with up to four times the mass of Jupiter, researchers suggest in the distant icy realm of the comet-birthing Oort cloud, which surrounds our solar system with billions of icy objects. The potential giant Jupiter would likely be a world so frigid it is difficult to spot, researchers said. It could be found up to 30,000 astronomical units from the sun. One AU is the distance between the Earth and the sun, about 93 million miles.
The giant planet is hidden in our Solar System according to scientists John Matese and Daniel Whitmire, from the University of Louisiana at Lafayette. According to the team, a colossus called Tyche is hidden in the Oort Cloud—the asteroid beehive that forms the outer shell of our home system, one light-year in radius. They claim that data already captured by NASA’s Wide-field Infrared Survey Explorer proves its existence.
Matese and Whitmire are convinced that Tyche composed mostly of hydrogen and helium is very real orbiting 15,000 times farther from the Sun than Earth, orbiting the Sun with moons and rings and an athmosphere with clouds and storm systems similar to Jupiter with a mild temperature (-73ºC/-99.4ºF).
If Tyche’s existence is confirmed, its Solar System planet status may not be debated that Tyche could be a planet born in another star system and captured by ours.
Many of the most well known comets, including Halley, Hale-Bopp and, most recently, McNaught, may have been born in orbit around other stars, according to a theory developed by an international team of astronomers in 2010 led by a scientist from the Southwest Research Institute in Boulder, Colo. The team used computer simulations to show that the Sun may have captured small icy bodies from its sibling stars while it was in its birth star cluster, creating a reservoir for observed comets.
While the Sun currently has no companion stars, it is believed to have formed in a cluster containing hundreds of closely packed stars that were embedded in a dense cloud of gas. During this time, each star formed a large number of small comets in a disk from which planets formed. Most of these comets were gravitationally slung out of these prenatal planetary systems by the newly forming giant planets, becoming tiny, free-floating members of the cluster.
The Sun’s cluster came to a violent end, however, when its gas was blown out by the hottest young stars. These new models show that the Sun then gravitationally captured a large cloud of comets as the cluster dispersed.
“When it was young, the Sun shared a lot of spit with its siblings, and we can see that stuff today,” says Dr. Hal Levison of the Southwest Research Institute.
Evidence for the team’s scenario came from the roughly spherical cloud of comets, known as the Oort cloud, that surrounds the Sun, extending halfway to the nearest star. It has been commonly assumed this cloud formed from the Sun’s proto-planetary disk. However, because detailed models show that comets from the solar system produce a much more anemic cloud than observed, another source is required.
“If we assume that the Sun’s observed proto-planetary disk can be used to estimate the indigenous population of the Oort cloud,” Levison says, “we can conclude that more than 90 percent of the observed Oort cloud comets have an extra-solar origin.”
“The formation of the Oort cloud has been a mystery for over 60 years and our work likely solves this long-standing problem,” says Brasser.
Just how safe is the Earth from a major comet impact event? Jupiter may hold the answer. On 1994 July 16-22, over twenty fragments of comet Shoemaker-Levy 9 collided with the planet Jupiter. The comet, discovered the previous year by astronomers Carolyn and Eugene Shoemaker and David Levy, was observed by astronomers at hundreds of observatories around the world as it crashed into Jupiter’s southern hemisphere. During July, 2010 a comet or asteroid ripped another Pacific-Ocean sized hole in Jupiter (image below). Is Jupiter a giant protective magnet for Earth, or are these events wake-up calls similar to Friday’s meteor explosion over Russia’s Ural Mountains?
As Stephen Hawking says, the general consensus is that any comet or asteroid greater than 20 kilometers in diameter that strikes the Earth will result in the complete annihilation of complex life – animals and higher plants. (The asteroid Vesta, for example, one of the destinations of the Dawn Mission, is the size of Arizona).
Since 1941 many astronomers have thought of Jupiter as a protective big brother for planet Earth -a celestial shield, deflecting asteroids and comets away from the inner Solar System. This long-standing belief that Jupiter acts as a celestial shield, deflecting asteroids and comets away from the inner Solar System, has been challenged by the first in a series of studies evaluating the impact risk to the Earth posed by different groups of object.
Dr Jonathan Horner of Great Britain’s Open University has studied the impact hazard posed to Earth by the Centaurs, the parent population of the Jupiter Family of comets. His research showed that the presence of a Jupiter-like planet in the Solar System does not necessarily lead to a lower impact rate at the Earth. Horner said that Jupiter’s role as guardian may have been overstated: “It seems that the idea isn’t so clear-cut.”
The idea of Jupiter as protector was first proposed by planetary scientist George Wetherill in 1941. Wetherill showed that the planet’s enormous mass — more than 300 times that of the Earth — is enough to catapult comets that might hit Earth, like a slingshot ,out of the Solar System.
Other astronomers have postulated that Jupiter’s gravitational pull would thin the crowd of dangerous asteroids and other objects, making Earth less impact prone. Other research has suggested that, in the past, changes in Jupiter’s orbit might have actually increased the number of objects on a collision course with earth. Until now, Horner says, little work was done to test either idea.
The short period Jupiter Family of Comets (JFCs) are believed to originate from the Kuiper Belt and have orbital periods of up to 20 years and low inclination controlled by Jupiter. The Kuiper Belt is a large reservoir of small icy bodies just beyond Neptune. From collisions or gravitational perturbations some Kuiper Belt objects escape and fall towards the Sun. When they approach the Sun their volatile elements will start to sublimate off the surface and we will see the object as a comet. Because the orbit crosses that of Jupiter, the comet will have gravitational interactions with this massive gas giant. The objects orbit will gradually change from these interactions and eventually the object will either be thrown out of the Solar System or collide with a planet or the Sun.
The second class of comets, the long periods, are believed to originate from the Oort cloud. This is a vast spherical reservoir believed to exist at the edge of the Solar System. The long period comets have periods of less than 200 years and no preference in orbital inclination.
“The idea that a Jupiter-like planet plays an important role in lessening the impact risk on potentially habitable planets is a common belief but there has only really been one study done on this in the past, which looked at the hazard due to the Long Period Comets,” Horner continued.” We are carrying out an ongoing series of studies of the impact risks in planetary systems, starting off by looking at our own Solar System, since we know the most about it.”
Horner and colleague Barrie Jones built several versions of the Solar System on the Open University’s computers: one with a Jupiter, one without, and several with a gas giant that was either a quarter, half, or three-quarters of Jupiter’s mass. The system also contained 100,000 centaurs — large, icy bodies from the Solar System’s Kuiper belt, within which Pluto lies.
After running their models for 10 million virtual years, Horner and Jones found some striking results:The Earth was about 30% more likely to be hit by a centaur in a Solar System with a life-size Jupiter than it was in a Jupiter-less system.
“We’ve found that if a planet about the mass of Saturn or a bit larger occupied Jupiter’s place,” Horner concluded, “then the number of impacts on Earth would increase. However if nothing was there at all, there wouldn’t be any difference from our current impact rate. Rather than it being a clear cut case that Jupiter acts as a shield, it seems that Jupiter almost gives with one hand and takes away with the other!”
The weakness of Horner’s tentative conclusion is that it fails to take into account Jupiter’s ability to deflect Earth-colliding objects from the Oort cloud, a massive cloud of comets that surrounds the Solar System
The Open University team is assessing the impact risk posed to the Earth by the asteroids and will go on to study the long period comets, before examining the role of the position of Jupiter within our system.
The fact that life appeared soon after the termination of the heavy bombardment about 3.8 billion years ago suggests that it seems reasonable that incoming comets and asteroids delivered the compounds essential for life.
The 2005 Deep Impact mission to Comet Tempel 1 discovered a mixture of organic and clay particles inside the comet that show it is overwhelmingly likely that life began in space, according to resaerch by Cardiff University scientists, professor Chandra Wickramasinghe and colleagues at the University’s Center for Astrobiology.
One theory for the origins of life proposes that clay particles acted as a catalyst, converting simple organic molecules into more complex structures. The 2004 Stardust Mission to Comet Wild 2 found a range of complex hydrocarbon molecules – potential building blocks for life.
The Cardiff team proposes the controversial theory that radioactive elements can keep water in liquid form in comet interiors for millions of years, making them potentially ideal “incubators” for early life. They also point out that the billions of comets in our solar system and across the galaxy contain far more clay than the early Earth did. The researchers calculate the odds of life starting on Earth rather than inside a comet at one trillion trillion (10 to the power of 24) to one against.
Professor Wickramasinghe said: “The findings of the comet missions, which surprised many, strengthen the argument for panspermia. We now have a mechanism for how it could have happened. All the necessary elements – clay, organic molecules and water – are there. The longer time scale and the greater mass of comets make it overwhelmingly more likely that life began in space than on earth.”
In his essay, Extraterrestrials: A Modern View, University of Washington professor Guillermo Gonzalez wrote: “The kind of origin of life theory a scientist holds seems to depend on his/her field of specialty: oceanographers like to think it began in a deep sea thermal vent, biochemists like Stanley Miller prefer a warm tidal pool on the Earth’s surface, astronomers insist that comets played an essential role by delivering complex molecules, and scientists who write science fiction part time imagine that the Earth was “seeded” by interstellar microbes.”
But Stephen Hawking asks “How many times in our galaxy alone has life finally evolved to the equivalent of our planets and animals on some far distant planet, only to be utterly destroyed by an impact?” Galactic history suggests it might be a common occurrence. Our cold comfort comes from the adjective “galactic” -that’s a hugely different time perspective that our biblical three score and ten.