Tag: mass extinction

BREAKING NEWS: Scientists to Determine Recent Supernovae Responsible for Earth’s Previous Mass Extinction

Dr Brian Thomas, an astrophysicist at Washburn University in Kansas, USA, modeled the biological impacts at the Earth’s surface, based on geologic evidence of nearby supernovae 2.5 million and 8 million years ago. In his latest paper, Thomas investigated cosmic rays from the supernovae as they propagated through our atmosphere to the surface, to understand their effect on living organisms.

How would a nearby supernova affect life on Earth? Thomas laments that supernovae often are exemplified as “supernova goes off and everything dies”, but that is not quite the case. The answer lies in the atmosphere. Beyond sunscreen, the ozone layer protects all biology from harmful, genetically altering ultraviolet (UV) radiation. Thomas used global climate models, recent atmospheric chemistry models and radiative transfer (the propagation of radiation through the layers of the atmosphere) to better understand how the flux of cosmic rays from supernovae would alter Earth’s atmosphere, specifically the ozone layer.

One thing to note is that cosmic rays from supernovae would not blast everything in their paths all at once. The intergalactic medium acts as a kind of sieve, slowing down the arrival of cosmic rays and “radioactive iron rain” (60Fe) over hundreds of thousands of years, Thomas tells Astrobiology Magazine. Higher energetic particles will reach Earth first and interact with our atmosphere differently than lower energy particles arriving later. Thomas’s study modeled the depletion in ozone 100, 300, and 1,000 years after the initial particles from a supernova began penetrating our atmosphere. Interestingly, depletion peaked (at roughly 26 percent) for the 300-year case, beating out the 100-year case.

The high-energy cosmic rays in the 100-year case would zip right through the stratosphere and deposit their energy below the ozone layer, depleting it less, while the less energetic cosmic rays arriving during the 300-year interval would deposit more energy in the stratosphere, depleting ozone significantly.

A decrease in ozone could be a concern for life on the surface. “This work is an important step towards understanding the impact of nearby supernovae on our biosphere,” says Dr Dimitra Atri, a computational physicist at the Blue Marble Space Institute of Science in Seattle, USA.

Thomas examined several possible biologically-damaging effects (erythema, skin cancer, cataracts, marine phytoplankton photosynthesis inhibition and plant damage) at different latitudes as a result of increased UV radiation resulting from a depleted ozone layer. They showed heightened damage across the board, generally increasing with latitude, which makes sense given the changes we see in the fossil record. However, the effects aren’t equally detrimental to all organisms. Plankton, the primary producers of oxygen, seemed to be minimally affected. The results also suggested a small increase in the risk of sunburn and skin cancer among humans.

So, do nearby supernovae result in mass extinctions? It depends, says Thomas. “There is a subtler shift; instead of a ‘wipe-out everything’, some [organisms] are better off and some are worse off.” For example some plants showed increase yield, like soybean and wheat, while other plants showed reduced productivity.  “It fits,” Thomas states, referring to the change in species in the fossil record.

In the future, Thomas hopes to expand on this work and examine possible linkages between human evolution and supernovae.

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New Study Proposes Short and Long Process of Extinction

A new study of nearly 22,000 fossils finds that ancient plankton communities began changing in important ways as much as 400,000 years before massive die-offs ensued during the first of Earth’s five great extinctions.

plankton

The research, published July 18 in the Early Edition of the Proceedings of the National Academy of Sciences, focused on large zooplankton called graptolites. It suggests that the effects of environmental degradation can be subtle until they reach a tipping point, at which dramatic declines in population begins.

“In looking at these organisms, what we saw was a disruption of community structures – the way in which the plankton were organized in the water column. Communities came to be less complex and dominated by fewer species well before the massive extinction itself,” says co-author H. David Sheets, PhD, professor of physics at Canisius College and associate research professor in the Evolution, Ecology and Behavior graduate program at the University at Buffalo.

This turmoil, occurring in a time of ancient climate change, could hold lessons for the modern world, says co-author Charles E. Mitchell, PhD, professor of geology in the University at Buffalo College of Arts and Sciences.

The shifts took place at the end of the Ordovician Period some 450 million years ago as the planet transitioned from a warm era into a cooler one, leading eventually to glaciation and lower sea levels.

“Our research suggests that ecosystems often respond in stepwise and mostly predictable ways to changes in the physical environment – until they can’t. Then we see much larger, more abrupt, and ecologically disruptive changes,” Mitchell says. “The nature of such tipping point effects are hard to foresee and, at least in this case, they led to large and permanent changes in the composition of the oceans’ living communities.

“I think we need to be quite concerned about where our current ocean communities may be headed or we may find ourselves at the tail end of a similar event – a sixth mass extinction, living in a very different world than we would like.” The study was a partnership between Canisius, UB, St. Francis Xavier University, Dalhousie University and The Czech Academy of Sciences.

A long slide toward oblivion

In considering mass extinction, there is perhaps the temptation to think of such events as rapid and sudden: At one moment in history, various species are present, and the next they are not.

This might be the conclusion you’d draw if you examined only whether different species of graptolites were present in the fossil record in the years immediately preceding and following the Ordovician extinction.

“If you just looked at whether they were present – if they were there or not – they were there right up to the brink of the extinction,” Sheets says. “But in reality, these communities had begun declining quite a while before species started going extinct.”

The research teased out these details by using 21,946 fossil specimens from areas of Nevada in the U.S. and the Yukon in Canada that were once ancient sea beds to paint a picture of graptolite evolution.

The analysis found that as ocean circulation patterns began to shift hundreds of thousands of years before the Ordovician extinction, graptolite communities that previously included a rich array of both shallow- and deep-sea species began to lose their diversity and complexity.

Deep-water graptolites became progressively rarer in comparison to their shallow-water counterparts, which came to dominate the ocean.

“There was less variety of organisms, and the rare organisms got rarer,” Sheets says. “In the aftermath of a forest fire in the modern world, you might find that there are fewer organisms left – that the ecosystem just doesn’t have the same structure and richness as before. That’s the same pattern we see here.”

The dwindling deep-sea graptolites were species that specialized in obtaining nutrients from low-oxygen zones of the ocean. A decrease in the availability of such habitats may have sparked the creatures’ decline, Sheets and Mitchell say.

“Temperature changes drive deep ocean circulations, and we think the deep-water graptolites lost their habitats as the climate changed,” Sheets says. “As the nature of the oceans shifted, their way of life went away.”