Tag Archives: extinction

Giant Comets Pose Threat To Life On Earth

Huge comets called centaurs deserve greater recognition as potential destroyers of life on Earth, according to a team of astronomers from the Armagh Observatory and the University of Buckingham. Measuring 50 to 100 kilometers (30 to 60 miles) across, these enormous masses of ice and rock have been identified in their hundreds over recent decades in the trans-Neptunian region the area beyond Neptune, which is the outermost planet in the Solar System.

However, these centaurs can make their way towards the inner planets as their orbits become deflected by the gravitational fields of Neptune, Uranus, and Saturn. Publishing a review of their research in Astronomy and Geophysics,the team estimates that centaurs are likely to cross the Earths orbit every 40,000 to 100,000 years.

Depending on the size, composition, and distance of a given comet, its effects on terrestrial ecosystems are likely to be highly variable. Because centaurs are thought to be unstable, the authors expect the majority of these effects to be caused by dust and other small fragments that result from the disintegration of the comets.

They estimate that a single centaur measuring 100 kilometers (60 miles) could contain about 100 times the mass of all the Earth-crossing asteroids detected to date. This translates to an awful lot of dust, leading the researchers to suggest that comets of this size could fill the Earths atmosphere with tiny particles, reducing the amount of sunlight that can pass through to roughly the level of moonlight, for up to 100,000 years. This, they say, would put an end to commercial agriculture.

A map of the Solar System, showing the orbits of several planets. In red are the orbits of 22 centaurs. In yellow are the orbits of 17 trans-Neptunian objects. Duncan Steel/Royal Astronomical Society

Additionally, larger fragments which could extend for several kilometers in length may generate catastrophic impacts, similar to that which is believed to have led to the extinction of the dinosaurs. According to the report, several such collisions may have occurred in the past, with the authors citing craters in the Gulf of Mexico, Ukraine, Siberia and Chesapeake Bay as likely candidates for centaur impact sites.

Given the probability of a centaur crossing Earths orbit at some point in the future, and the sheer volume of debris caused by the disintegration of these comets, the team claims that some level of impact is inevitable, although the nature and extent of the effects are likely to depend on various factors.

At present, attempts to quantify Earths risk of being affected by a collision are centered around NASAs Spaceguard initiative, which seeks to map up to 90 percent of near-Earth objects (NEOs) larger than 1 kilometer (0.6 miles). This programfocuses mainly on the asteroid belt that sits between Mars and Jupiter, although Professor Bill Napier, who helped to conduct this research, is now calling for the scope of this search to be extended to the outer reaches of the Solar System.

Our work suggests we need to look beyond our immediate neighborhood and look out beyond the orbit of Jupiter to find centaurs, he said in a statement. If we are right, then these distant comets could be a serious hazard, and it’s time to understand them better.

Read more: http://www.iflscience.com/space/giant-comets-pose-potential-threat-earth

New Analysis Suggests Sixth Mass Extinction Could Occur By 2200

We’ve already been warned that our planet faces a sixth mass extinction, and some even believe that we are already in the early stages of such an event. Now, the harsh reality of the impending situation has been highlighted by the scientific journal Nature, with a special report detailing the threats that major animal groups face. According to the analysis, those predicted to take the greatest hit are amphibians, with an alarming 41% of species within this group facing extinction. But mammals and birds won’t get off lightly, with 26% and 13% of species similarly threatened, respectively.

Among the known critically endangered species are numerous different primates, such as the snub-nosed monkey, black rhinos, the yangtzee river dolphin, western gorillas and the Amur leopard. But many species that are currently only listed as endangered also face being wiped out, such as bonobos and loggerhead turtles.

The primary driver? Humans. According to the Living Planet Index, exploitation—such as hunting and fishing—is playing a major role in triggering the decline in animal species. Other human activities that are helping obliterate populations include agriculture and urbanization, whereby large areas of wild habitats are destroyed to make way for buildings, infrastructure, livestock and crops.

Climate change, which is primarily due to humans, is also threatening many sensitive animals, such as polar bears and corals, and will probably accelerate extinctions in ways that are currently unknown. Increasing CO2 emissions are not only warming our planet and seas, but they are acidifying our oceans, making them a more hostile environment for marine organisms. It’s estimated that 10% of all Earth’s coral reefs are already degraded beyond recovery, and if current pressures continue, 60% could be dead by 2050.

While we know that the situation is not good for many organisms on Earth, attempting to predict how quickly species are likely to disappear is extremely difficult, which only exacerbates the problem. Much of the uncertainty comes from the fact that we only know about a fraction of our planet’s biodiversity, and many unknown groups often reside in small areas that are already being demolished by humans and may never be assessed.

When scientists attempt to assess the number of species of animals, plants and fungi alive today, estimates are wildly varied, ranging from around two million to more than 50 million. Not only that, but approximations of the rate of extinction also vary, ranging from 0.01% to 0.7%, meaning the number of species disappearing is somewhere between 500 and 36,000 a year. If we use the upper rate, a mass extinction—or loss of 75% of species—could occur within the next few hundred years. At the lower rate, however, it may not arrive for thousands of years.

Five mass extinction events have occurred before, all of which were triggered by either natural planetary transformations or asteroid strikes. But the impending 6th event will be the work of humans, who have been gradually wiping out animals since mammoths and mastodons during prehistoric times.

So what can we do? According to the report, it’s of fundamental importance that countries start extending protected areas and devoting more resources to counting and evaluating stocks of life on Earth before they disappear.

[Via Nature, Nature, The Guardian and The Independent]

Read more: http://www.iflscience.com/plants-and-animals/new-analysis-suggests-sixth-mass-extinction-could-occur-2200

Climate Change Killed The Last Ichthyosaurs

Ichthyosaurs became extinct in the Late Cretaceous about 90 million years ago thats roughly 28 million years before the mass extinction event that wiped out all non-avian dinosaurs at the end of the Cretaceous. According to a new Nature Communications study published this week, the extinction of these dolphin-shaped marine reptiles occurred in two phases driven by climate instability and reduced evolutionary rates.

Researchers have previously proposed that the earlier demise of ichthyosaurs after their 157-million-year reign was because of an increase in competition with other marine reptiles or a drop in their food resources, soft cephalopods in particular. But recent studies suggested that ichthyosaurs were richly diverse up to just a few million years before their extinction, so the overall cause of their disappearance is still a mystery.

To investigate, a team led by University of Oxfords Valentin Fischer estimated ichthyosaur diversity over time by studying their evolutionary relationships. They assembled this so-called phylogenetic dataset using 88 characters from 36 ichthyosaur groups, including three-fourths of all known species from the Late Jurassic and Cretaceous. The team also estimated ecological diversity in terms of diet using a series of measurements on skulls and teeth, and they examined the wide range of differences in ichthyosaur body shapes and forms. They then correlated these results with environmental data ranging from ocean chemistry to sea level change.

Ichthyosaurs were highly diverse throughout the Early Cretaceous, but they were evolving slowly. These findings support climate change as a main driver of changes in marine ecosystems, and they fit with the hypothesis that ichthyosaurs were outcompeted by other marine reptiles and fishes. Additionally, the team identified an earlier extinction event that occurred about 100 million years ago. The earlier event eliminated most of their ecological diversity, and a second event about 94 million years ago finished them off, Fischer explains to IFLScience.

Ichthyosaurs faced an abrupt two-phase extinction linked to reduced evolutionary rates and environmental volatility. The beginning of the Late Cretaceous was a peculiar period of numerous climatic and oceanic disturbances, the authors write, with no polar ice, extremely high sea levels, unique sedimentation, strong anoxia, and high temperatures and carbon dioxide concentrations.

Read more: http://www.iflscience.com/plants-and-animals/climate-change-killed-last-ichthyosaurs

Building Of Dams In The Amazon Will Cause “Countless” Extinctions

Considering the Amazon accounts for around a fifth of all water discharged by rivers globally, it is unsurprising that the river system is considered to have great potential for hydroelectric power. This has given rise to 191 dams that have already been built by nine countries through which the Amazon River flows, and with 243 more in the pipeline it seems the dam building boom is showing no signs of slowing anytime soon.

But a new study has found that while these hydroelectric projects might have great green renewable credentials on paper, they could contribute to the extinction of countless species. The Amazon rainforest is home to hundreds, if not thousands, of species of animals from fish to bats to primates that are only found in highly localized conditions. Known as endemic species, sometimes they have a range of no more than a few square kilometers. As dams are built and the subsequent lagoon floods vast tracts of forest, they will destroy all the known habitat for certain animals, wiping them out forever.

The result of a dam in the Rio Candeis, which flooded hundreds of kilometers of once virgin rainforest.Joelle Hernandez/ Flickr CC BY-NC-ND 2.0

Our research shows that an expansion of the dam network will result in huge changes to these Amazonian rivers by obstructing movement of aquatic fauna both upstream and downstream, by submerging rapids under huge lakes, by flooding adjacent forests and by creating forest islands that cannot sustain viable animal and plant populations, explains Professor Carlos Peres from the University of East Anglia, who led the research published in Biodiversity and Conservation.

Ironically though, many of the species that could be negatively hit and even driven to extinction by the massive expansion of dam building projects in the Amazon are protected against international trade. Yet there is nothing to protect them if dams are built and their habitat is destroyed by the multitude of renewable energy projects, favored for their cheap generation of electricity.

This isnt the first time that hydroelectricitys green credential has been called into question. An earlier study showed how the building of Brazils largest dam, which formed a reservoir covering 2,360 square kilometers (910 square miles), dramatically reduced the number of species living there, with most of the region now completely devoid of wildlife. Not only that, but the species that do survive are often generalist or invasive species, further harming the region’s biodiversity.

The 600,000-square-kilometer Sao Simao reservoir created by a hydroelectric plant in Brazil as seen from the ISS. NASA

A further knock to the green image is that dams are known to be massive net contributors to CO2 and methane emissions, as the trees and organic matter that reservoirs cover rot down and decompose. One estimate states that in 1990 the greenhouse effect of the emissions from one dam in Brazil was actually three and half times what it would have been if the energy was sourced from oil instead. These harmful emissions are particularly pronounced in tropical regions, such as the Amazon, as the temperature favors the rapid decomposition of plants, and thus the formation of methane.

Yet countries like Brazil dont need to go down this route. The planned dams are not an inevitable part of Brazils future development because they are not necessary, says Dr. Phillip Fearnside, one of the coauthors of the latest study. Brazil has many better options, including investing in energy efficiency and tapping the countrys vast potential wind and solar resources. The severe impacts of Amazonian dams make pursuing other options very much in Brazils best interest.

Main image: Bill Ohl/Flickr CC BY-ND 2.0

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Read more: http://www.iflscience.com/environment/building-dams-amazon-will-cause-countless-extinctions

Humans, Not Climate Change, To Blame For Ice Age Animal Extinction

Our last glacial period lasted from about 115,000-12,500 years ago. By the end, 177 large mammal species had gone extinct. There has been considerable debate over the last half century regarding what caused the loss of these animals, including saber-tooth cats, mastadons, and giant sloths. While many have argued that these animals simply weren’t able to adapt to the warmer climate, others blame human activity. A new study led by Jens-Christian Svenning of Aarhus University has strongly suggested that humans are squarely responsible for the disappearance of megafauna during the last 100,000 years. The results have been published in the Proceedings of the Royal Society B.

For this study, the researchers focused on megafauna, which is categorized as animals weighing at least 10 kg (22 lbs) that lived in the last 132,000 years. They also identified the regions where these animals lived, comparing the data with climate and human activity. While there are invariably going to be animals lost after a great climate change such as the ending of an ice age, the loss of megafauna that followed the most recent glacial event is an anomaly when compared to the ending of other ice ages.

“Our results strongly underline the fact that human expansion throughout the world has meant an enormous loss of large animals,” co-author Søren Faurby said in a press release.

The team had identified that out of the 177 large mammals that went extinct, 62 species were native to South America, 43 from North America, 38 from Asia, 26 from Australia and the surrounding region, 19 from Europe, and 18 of the extinct species were from Africa. Surprisingly,  the areas where the animals went extinct spanned all climate regions, even the warmer regions that hadn’t been particularly affected by the ice age. While there is a slight correlation between the changing climate and the animals dying out, the researchers feel it isn’t nearly strong enough to explain such a drastic series of events across the globe. If anything, it would only explain the extinctions in Eurasia.

“The significant loss of megafauna all over the world can therefore not be explained by climate change, even though it has definitely played a role as a driving force in changing the distribution of some species of animals,” lead author Christopher Sandom explained. “Reindeer and polar foxes were found in Central Europe during the Ice Age, for example, but they withdrew northwards as the climate became warmer.”

Unfortunately, the correlation between extinctions and human activity was quite strong. Hunting activity is believed to be the root cause of the animals’ extinction, through both direct and indirect methods. Humans either hunted the animals themselves, or competed with them for smaller prey. With the animals’ food source gone, they wouldn’t be able to sustain their populations.

“We consistently find very large rates of extinction in areas where there had been no contact between wildlife and primitive human races, and which were suddenly confronted by fully developed modern humans (Homo sapiens). In general, at least 30% of the large species of animals disappeared from all such areas,” stated Svenning.

The extinction of these ice age animals is not completely unlike the overhunting that has threatened the lives of modern megafauna, including sharks, rhinoceroses, elephants, and big cats, such as the tiger. These results also support a paper published in March in which genetic analyses revealed that humans drove Moas to extinction so quickly, it didn’t even have time to affect the birds’ biodiversity. An unrelated study a week later suggested that woolly mammoths suffered inbreeding depression, likely due to a declining population from human hunting, making severe birth defects common before the species went extinct.

[Header image “Spring Break 2013: Day 4” by Jennifer Carole via flickr, used in accordance with CC BY-ND 2.0 and has been cropped to fit]

Read more: http://www.iflscience.com/plants-and-animals/humans-not-climate-change-blame-ice-age-animal-extinction