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April 1, 2024
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apr 3, 300000 - WR104 supernova

Description:

At some point in the next "several" hundred thousand years, the Wolf-Rayet star WR 104 is expected to explode in a supernova. It has been suggested that it may produce a gamma ray burst that could pose a threat to life on Earth should its poles be aligned 12° or lower towards Earth. The star's axis of rotation has yet to be determined with certainty.

A gamma-ray burst, beamed directly at Earth is pretty unlikely. However, if one did, the amount of damage would depend on how close the burst is. Let's assume that one occurred in the Milky Way galaxy, but very far away from our solar system.
With the gamma-rays beamed directly at us, the radiation would destropy a significant portion of our atmosphere, specifically the ozone layer. The photons streaming from the burst would cause chemical reactions leading to photochemical smog. This would further deplete our protection from cosmic rays. Then there are the lethal doses of radiation that surface life would be experience. The end result would be mass extinctions of most species of life on our planet.

Abstract: Gamma-ray bursts (GRBs) are likely to have made a number of significant impacts on the Earth during the last billion years. The gamma radiation from a burst within a few kiloparsecs would quickly deplete much of the Earth’s protective ozone layer, allowing an increase in solar ultraviolet radiation reaching the surface. This radiation is harmful to life, damaging DNA and causing sunburn. In addition, NO2 produced in the atmosphere would cause a decrease in visible sunlight reaching the surface and could cause global cooling. Nitric acid rain could stress portions of the biosphere, but the increased nitrate deposition could be helpful to land plants. We have used a two-dimensional atmospheric model to investigate the effects on the Earth’s atmosphere of GRBs delivering a range of fluences, at various latitudes, at the equinoxes and solstices, and at different times of day. We have estimated DNA damage levels caused by increased solar UVB radiation, reduction in solar visible light due to NO2 opacity, and deposition of nitrates through rainout of HNO3.

A GRB within a few parsecs that is directed at the Earth will impact one hemisphere of the planet with a short, but intense blast of high-energy photons. Gamma-rays and X-rays are highly attenuated by the Earth’s atmosphere. Therefore, the ground-level effects are primarily indirect. A small fraction of the incident energy reaches the ground as dangerous ultraviolet (UV) radiation (Smith et al. 2004), but this is limited in time to the duration of the event, which is at most 10’s of seconds for a long burst, and is less than a seconds for a short burst. While it is possible that this flash would affect some organisms, it seems unlikely that a biological catastrophe would result from this effect alone. Of course, for planets with thinner atmospheres the energy deposited at the ground would be greater and more serious effects may be expected (Smith et al. 2004; Galante & Horvath 2007). We are concerned here with effects on life on Earth and so will concentrate on the longer-term impacts.


There are three potentially harmful long-term effects of a GRB that follow from changes in atmospheric chemistry (Reid & McAfee 1978). High-energy photons cause dissociation, GRBs and Life on Earth 3 ionization and ionizing dissociations of N2 and O2 in the atmosphere. Subsequent reactions lead to the formation of nitrogen oxides, most importantly NO and NO2. These compounds catalytically deplete ozone (O3) in the stratosphere, leading to increases in surface-level solar UV over long time periods (years). Secondly, NO2 itself is a brown gas that absorbs strongly in the visible. This may potentially have a climatic effect by reducing solar insolation at the ground, thereby leading to cooling. Third, the atmosphere returns to normal via the removal of nitrogen oxides by way of precipitation of nitric acid (HNO3).

While nitric acid rain can have a negative effect on a variety of organisms (including amphibians), it appears that the amount deposited following a GRB would be small enough so as to not have a serious impact (Thomas & Honeyman 2008). There is a possibility that the deposited nitrate may actually benefit some organisms, particularly land plants that may be nitrogen starved.

It is currently unclear whether cooling due to NO2 opacity is likely to be important. Our results indicate a global average reduction of about 1% in solar visible light fluence, lasting a few years (Melott et al. 2005). Larger reductions would occur at the poles, where compounds produced by the burst tend to accumulate (due to poleward transport in the stratosphere). It is possible that this reduction in sunlight could initiate a global cooling event, particularly if the climate is near a “tipping point.” To date no simulations of the climate effects have been performed, but our data is available for such work.

For our standard fluence, full recovery takes just over a decade.

A variety of effects on organisms may be expected due to the enhanced surface level solar UV following severe depletion of ozone. The UVB (290-315 nm) part of the spectrum is most affected by O3 levels and is known to damage DNA molecules directly but can also have effects on other biomolecules as well (Vincent and Neale 2000). UVB effects appear at the organism level in ways ranging from lowered metabolic rates and photosynthetic capacity, low growth GRBs and Life on Earth 4 rate, delayed or arrested cell division and/or death. In multicellular organisms, the effects may cause developmental delay and abnormalities, altered tissue composition and cancer.

Using this approach, we find DNA damage of up to 16 times the annual global average of preburst values. This level of damage lasts a few months in some areas, particularly at mid-latitudes during the summer. Those locations may experience 5-7 times the normal damage level for a period of several years.

So if a gamma ray burst went off within about 5000-8000 light years, we’d be in a world of trouble.

The oxides of nitrogen produced in the upper atmosphere are not concentrated enough to have an effect at ground level and this new research shows that ozone levels at ground level are not high enough to be hazardous even for a very close gamma ray burst. So the main effects are from the UV. So if a gamma ray burst causes extinctions then it would be due to the increased levels of UV light at ground level until the ozone hole heals. But this is something humans can protect ourselves against easily. 

The effects of a nearby gamma ray burst or supernova, even if it is as close as just a few light years away would be just on the upper atmosphere on the ozone layer leading to more UV radiation - an ozone hole - and possibly nitric acid rain. The ionizing radiation effects are not significant.

Without ozone layer:
1. Immediate effects. In plants, UV-B generally reduces size, productivity and quality through impairing photosynthesis (let’s remember that forests alone are estimated to cover approx. 30% of Earth’s surface) - their rapid deterioration would begin immediately.

In regards to humans and animals - even with our ozone layer, we can’t stare at the Sun for more than 60 seconds without risking blindness - with a 100% decrease of ozone, blindess could set in immediately. Also, remember that human skin can burn and begin to boil after even less than a day of being in the Sun - imagine if our ozone layer was to be fully removed.
The conscious world would be thrusted into darkness and screaming frenzy as the agony of their obliterated cataracs is overcome by that of their skin blistering and scorching to nothing.

2. Subsequent effects. Our world would be entirely different within days. The majority of surface-dwelling animal and plant life would either melt or shrink away. Any humans remaining on the surface would find themselves quickly soccombing to cancer or deterioration of their organs (The United Nations Environment Program estimates that a sustained 1 percent depletion of ozone will ultimately lead to a 2-3 percent increase in the incidence of non-melanoma skin cancer).
Any sub-surface humans that have managed to escape the effects of radiation might be able to survive with an abundance of non-perishable food, however as aforementioned, ALL vegetation and crops would be decimated, taking sustainability off the table.

3. Mid-term effects. Our atmospheric chemical composition would begin to change dramatically. Eco-systems making vital part of biogeochemical cycles that make the world as we know it would have collapsed, having major effects on carbon and energy cycles throughout Earth.
The decimation of plant life would radically reduce the atmospheric concentration of oxygen and greatly increase that of carbon (Approx. 45% of land-stored carbon is in forests). Also note that phytoplankton storing huge amounts of carbon in the ocean would be greatly reduced in population, further increasing atmospheric carbon concentration.
Our atmosphere would flip, chemically speaking, from a heavy concentration of oxygen to CO2.

Perhaps eventually we could see life re-emerging slowly as traits such as reduced oxygen-concentration requirements and increased cellular resistance to UV radiation evolve via natural selection and mutation in both plants and animals. Life could still thrive - but its distinctly “Earthly” character would never be the same. Earth would never be the same - at least not for millions of years.

With the massive die-off of plants, CO2 levels would skyrocket and oxygen levels would drop. This would, of course, result in the end of animal life. The lack of plants as food would also lead to mass starvation.

Within days of the ozone layer's disappearance, many plants would die. The intensity of the sun's radiation would make photosynthesis — a process by which plants convert light energy into chemical energy to fuel their growth — an impossibility for all but the largest and slowest-growing florae. And even these holdouts, primarily massive trees, would eventually die, too. Without plants, the food chain would collapse. Herbivores would starve. Omnivores and carnivores could feed off their bodies for a time, but their food supply would dwindle and cause widespread extinction [source: 

• It will be 30-40 degree Celsius more than General average temperature of the earth.
• It is because ozone prevent the ultraviolet rays to reaching the earth surface.
• Ultraviolet rays have short wavelength and high energy, it increases the earth temperature.

Ozone is a green house gas and has some atmospheric effects. Clear evenings could potentially be colder as the Ozone isn't there to trap heat in the same way and more would escape. This is going to have some weather effects...Ozone intercepts much of the UVR and in doing so heats up the upper atmosphere, in particular the thermosphere. Honestly I have no clue what reducing Ozone would do in this case...less active thermosphere maybe?

No clue on behaviour aspects here...temperatures may vary more heavily, especially in drier climates. More UVR striking the ground will warm it heavier during the day (and potentially increase humidity), while the evening sky will lack the ozone greenhouse effect and allow for additional cooling. There is the potential that sea surface temperatures will rise due to the additional heat from UVR, and if this is the case, tropical storms could become more powerful. Very speculative here.

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2 Jan 2018
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apr 3, 300000
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~ 298173 years later
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