Read moreBased on the concentration of Fe-60 in the crust, Knie estimated that the supernova exploded at least 100 light-years from Earth—three times the distance at which it could’ve obliterated the ozone layer—but close enough to potentially alter cloud formation, and thus, climate. While no mass-extinction events happened 2.8 million years ago, some drastic climate changes did take place—and they may have given a boost to human evolution. Around that time, the African climate dried up, causing the forests to shrink and give way to grassy savanna. Scientists think this change may have encouraged our hominid ancestors as they descended from trees and eventually began walking on two legs.
That idea, as any young theory, is still speculative and has its opponents. Some scientists think Fe-60 may have been brought to Earth by meteorites, and others think these climate changes can be explained by decreasing greenhouse gas concentrations, or the closing of the ocean gateway between North and South America. But Knie’s new tool gives scientists the ability to date other, possibly more ancient, supernovas that may have passed in the vicinity of Earth, and to study their influence on our planet. It is remarkable that we can use these dull, slow-growing rocks to study the luminous, rapid phenomena of stellar explosions, Fields says. And they’ve got more stories to tell.
climate change
“If our hypothesis for Mount Sharp holds up, it challenges the notion that warm and wet conditions were transient, local, or only underground on Mars,” said Ashwin Vasavada, Curiosity deputy project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California. “A more radical explanation is that Mars’ ancient, thicker atmosphere raised temperatures above freezing globally, but so far we don’t know how the atmosphere did that.”
Why this layered mountain sits in a crater has been a challenging question for researchers. Mount Sharp stands about 3 miles (5 kilometers) tall, its lower flanks exposing hundreds of rock layers. The rock layers – alternating between lake, river and wind deposits – bear witness to the repeated filling and evaporation of a Martian lake much larger and longer-lasting than any previously examined close-up.
“We are making headway in solving the mystery of Mount Sharp,” said Curiosity Project Scientist John Grotzinger of the California Institute of Technology in Pasadena. “Where there’s now a mountain, there may have once been a series of lakes.”
Curiosity currently is investigating the lowest sedimentary layers of Mount Sharp, a section of rock 500 feet (150 meters) high, dubbed the Murray formation. Rivers carried sand and silt to the lake, depositing the sediments at the mouth of the river to form deltas similar to those found at river mouths on Earth. This cycle occurred over and over again.
“The great thing about a lake that occurs repeatedly, over and over, is that each time it comes back it is another experiment to tell you how the environment works,” Grotzinger said. “As Curiosity climbs higher on Mount Sharp, we will have a series of experiments to show patterns in how the atmosphere and the water and the sediments interact. We may see how the chemistry changed in the lakes over time. This is a hypothesis supported by what we have observed so far, providing a framework for testing in the coming year.”
After the crater filled to a height of at least a few hundred yards, or meters, and the sediments hardened into rock, the accumulated layers of sediment were sculpted over time into a mountainous shape by wind erosion that carved away the material between the crater perimeter and what is now the edge of the mountain.
On the 5-mile (8-kilometer) journey from Curiosity’s 2012 landing site to its current work site at the base of Mount Sharp, the rover uncovered clues about the changing shape of the crater floor during the era of lakes.
Read moreRead morePolynesians were able to sail downwind to Easter Island and New Zealand centuries ago, a new analysis of past climate has found. There were narrow windows of time between 1140 and 1260 AD where the winds allowed this, say researchers in this week’s Proceedings of the National Academy of Sciences. “It’s really incredible to think that for a 120-year period the Polynesians took advantage of these windows of opportunities and they crossed almost a third of the surface of the Earth,” says co-author Associate Professor Ian Goodwin of Macquarie University. Archaeological evidence suggests that from around 1000 years AD, Polynesians travelled in their ocean-sailing canoes east from Samoa to what is known as Central East Polynesia (CEP) – which includes Society, Tuamotu, Marquesas, Gambier, Southern Cook and Austral Islands. In a short period between 1140 and 1260 AD they then migrated on to New Zealand and Easter Island. “It’s always been quite a mystery as to why there was a concentration of colonisation in a period of a couple of hundred years and why it ceased after that,” says Goodwin. Especially since, according to today’s prevailing winds, travelling to these later destinations would have been against the wind for most of the time, he adds. While some researchers have proposed Polynesians must have had much more complex canoes than have been found to date, Goodwin and colleagues suggest this was not necessary. They have found that during this short time there were actually a number of ‘climate windows’, lasting around 20 years each, where the winds were in favour of the long voyages to New Zealand and Easter Island.
Read moreSubstitute any disturbance for El Niño, including those linked to human activity, and we have a way to think about other hybrids, like the coywolves or grolar bears or, in fact, ourselves. Some argue that Homo sapiens left Africa when its northern deserts were passable — that is, at a moment when the climate changed. We bumped into long-lost relatives in Eurasia, the equivalent of today’s polar bears in the grolar bears’ story, and mated.
We may, in turn, have adapted to Eurasian conditions by borrowing genes from these “locals.” Everyone except sub-Saharan Africans carry a small quantity of Neanderthal DNA that includes traits possibly important for survival in Eurasian environments — immune-system and skin-pigmentation genes, among others. And our current genome warehouses DNA from archaic humans that have otherwise disappeared. A recent study estimated that, in the same way that coywolves can be said to store wolf DNA that might have otherwise vanished from the Northeast, one-fifth of the Neanderthal genome endures, dispersed throughout humanity.
So why don’t we see advanced civilizations swarming across the Universe? One problem may be climate change. It is not that advanced civilizations always destroy themselves by over-heating their biospheres (although that is a possibility). Instead, because stars become brighter as they age, most planets with an initially life-friendly climate will become uninhabitably hot long before intelligent life emerges.
The Earth has had four billion years of good weather despite our Sun burning a lot more fuel than when Earth was formed. We can estimate the amount of warming this should have produced thanks to the scientific effort to predict the consequences of man-made greenhouse-gas emissions.
These models predict that our planet should warm by a few degrees centigrade for each percentage increase in heating at Earth’s surface. This is roughly the increased heating produced by carbon dioxide at the levels expected for the end of the 21st century. (Incidentally, that is where the IPCC prediction of global warming of around three degrees Celsius comes from.)
Over the past half-billion years, a time period for which we have reasonable records of Earth’s climate, the Sun’s surface temperature increased by four percent, and terrestrial temperatures should have risen by roughly 10 degrees Celsius. But the geological record shows that, if anything, on average temperatures fell.
Simple extrapolations show that over the whole history of life, temperatures should have risen by almost 100 degrees Celsius. If that were true, early life must have emerged upon a completely frozen planet. Yet, the young Earth had liquid water on its surface. So what’s going on?
The answer is that it’s not only the Sun that has changed. The Earth also evolved, with the appearance of land plants around 400 million years ago changing atmospheric composition and the amount of heat Earth reflects back into space. There has also been geological change with the continental area steadily growing through time as volcanic activity added to the land-mass. This too had an effect on the atmosphere and Earth’s reflectivity.
Remarkably, biological and geological evolution have generally produced cooling, and this has compensated for the warming effect of our aging Sun. There have been times when compensation was too slow or too fast, and the Earth warmed or cooled, but not once since life first emerged has liquid water completely disappeared from the surface.
Our planet has therefore miraculously moderated climate change for four billion years. This observation led to the development of the Gaia hypothesis that a complex biosphere automatically regulates the environment in its own interests. However, Gaia lacks a credible mechanism and has probably confused cause and effect: a reasonably stable environment is a precondition for a complex biosphere, not the other way around.
Other inhabited planets in the Universe must also have found ways to prevent global warming. Watery worlds suitable for life will have climates that, like the Earth, are highly sensitive to changing circumstances. The repeated canceling of star-induced warming by “geobiological” cooling, required to keep such planets habitable, will have needed many coincidences, and the vast majority of such planets will have run out of luck long before sentient beings evolved.
http://arstechnica.com/science/2014/06/why-havent-we-encountered-aliens-yet-the-answer-could-be-climate-change/ (via fuckyeahdarkextropian)
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A solar system full of dead worlds and moons.
Dried up sea beds of underground oceans rich in the fossils of life that lasted just a while. And the ones that made it in their own unique way.
Let’s go see.
These species were not just ornaments of the natural world. The new work presented at the conference suggests that they shaped the rest of the ecosystem. In Britain during the last interglacial period, elephants, rhinos and other great beasts maintained a mosaic of habitats: a mixture of closed canopy forest, open forest, glade and sward. In Australia, the sudden flush of vegetation that followed the loss of large herbivores caused stacks of leaf litter to build up, which became the rainforests’ pyre: fires (natural or manmade) soon transformed these lush places into dry forest and scrub.
In the Amazon and other regions, large herbivores moved nutrients from rich soils to poor ones, radically altering plant growth. One controversial paper suggests that the eradication of the monsters of the Americas caused such a sharp loss of atmospheric methane (generated in their guts) that it could have triggered the short ice age which began about 12,800 years ago, called the Younger Dryas.
Read moreRead moreHindle contrasted the government’s response to fracking – setting up a new agency, the Office of Unconventional Gas and Oil, to support the industry – with the lack of political interest in biogas, which is rarely mentioned by ministers.
One reason biogas has received less attention is that it falls between three government departments – energy, environment and communities and local government.
At present, according to estimates from the government’s Waste Resource and Action Programme, the UK throws away 15m tonnes of food waste a year, from homes, industry and retail. Only about 1m tonnes of the waste is used to generate biogas, or methane, using anaerobic digestion techniques that are well-established in other parts of the world.
This diverts resources to landfill and gives rise to greenhouse gas emissions, because the rotting food produces methane that is not captured and adds to the concentration of carbon in the air.
About 90m tonnes of animal waste is also produced in the UK each year, only a tiny portion of which is used for energy production. Sewage treatment plants are also overlooked. Biogas can be poured into the national gas grid and used for heating homes, burned to generate electricity, or used in specially adapted vehicles.
The Committee to Nuke Elysium 