Spiral Arms, Supernovae, & Mass Extinctions

[Widdekind]

Is this a plausible scenario (?) — please comment

 

 

Prof. Richard A. Muller has shown that the Lunar cratering rate actually increased, beginning about 400 Mya*:

By extension, the cratering rates on the Earth, and even across the Inner Solar System, likely increased too, from ~400 Mya.

*

PBS

Exploring Space — The Quest for Life

(DVD)

 

 

 

A.J. Meadows (The Future of the Universe, pp. 118-125) says that, as our Sun orbits around the Galaxy, it travels into, thru, and out of, our Galaxy's Spiral Arms; and, that these can cause close encounters with Star Forming Regions, on ~200-500 Myr time scales:

The Sun is currently positioned near the edge of a Spiral Arm... The local arm, and the Sun, are moving at different speeds, so that Sun is not a permanent member of the arm... So, the Sun is sometimes embedded in a Spiral Arm, and sometimes not. Encounters between the Sun, and a Spiral Arm, occur every

few hundred million years

... How near the Sun ventures to newly forming stars [in Interstellar Clouds, in Spiral Arms] will vary from from one passage through a Spiral Arm to the next. Big Interstellar Clouds, where new stars preferentially form, are often fairly isolated from each other. The spaces between them are usually several times the size of the individual clouds. Consequently, the Sun may only encounter a big cloud in every 5-10 spiral-arm passages, so it is difficult to guess what any individual passage will bring, in terms of Cosmic Rays (CRs) [from young stars, formed from Interstellar Clouds]. Still, looking to the future, we can predict, that

the Earth will face increased exposure to CRs every

few hundred million years

or so — in reasonable agreement w/ the past frequency measured from meteorites. But, we can add that, once or twice in the

next billion years

, the Solar System can expect to receive a really massive dose of CRs.

And, in addition, the Ordovician Mass Extinction Event (~450 Mya) could, conceivably, have been caused by a powerful Supernova explosion occurring near our Solar System*.

*

Wikipedia

; History Channel

Mega Disasters — Gamma Ray Burst

(TV); Animal Planet

Animal Armageddon — Death Rays

(DVD)).

 

 

 

Finally, the KT Mass Extinction Event (~65 Mya) was probably caused by an asteroid born from the Baptistina Family, the rubbled remains of a massive body which was broken apart about 160 Mya (and likely caused the crater Tycho on the Moon, about 110 Mya, as well)*. This shows that gravitational disturbances can take ~50 Myr to propagate down into the Inner Solar System, and that they can last for as long as ~100 Myr.

*

Wikipedia

; History Channel

Jurassic Fight Club — Armageddon

(DVD); National Geographic

Naked Science — Dino Meteor

[??] (TV)

 

 

 

All this seemingly suggests a scenario, wherein, during a transit across a Spiral Arm, our Sun closely encountered a Star Forming Region & Supernova ~450 Mya. Radiation from the Supernova immediately caused the Ordovician Mass Extinction, but was also associated with a gravitational disturbance of the Oort Cloud — which, after a further ~50 Myr, caused increased cratering rates across the Inner Solar System (called a "Comet Swarm"). Perhaps there is even some kind of connection to the vigorous resurfacing events on Venus over the last 300-500 Myr.

[jake.com]

The Ordovician–Silurian extinction events are currently being intensively studied; the most commonly accepted theory is that they were triggered by the onset of a long ice age, perhaps the most severe glacial age of the Phanerozoic, in the Hirnantian faunal stage that ended the long, stable greenhouse conditions typical of the Ordovician. The event was preceded by a fall in atmospheric CO2, which selectively affected the shallow seas where most organisms lived. As the southern supercontinent Gondwana drifted over the South Pole, ice caps formed on it. The strata have been detected in late Ordovician rock strata of North Africa and then-adjacent northeastern South America, which were south-polar locations at the time. Glaciation locks up water from the world-ocean, and the interglacials free it, causing sea levels repeatedly to drop and rise; the vast shallow intra-continental Ordovician seas withdrew, which eliminated many ecological niches, then returned, carrying diminished founder populations lacking many whole families of organisms. Then they withdrew again with the next pulse of glaciation, eliminating biological diversity at each change). In the North African strata, Julien Moreau reported five pulses of glaciation from seismic sections.

 

This incurred a shift in the location of bottom-water formation, shifting from low latitudes, characteristic of greenhouse conditions, to high latitudes, characteristic of icehouse conditions, which was accompanied by increased deep-ocean currents and oxygenation of the bottom-water. An opportunistic fauna briefly thrived there, before anoxic conditions returned. The breakdown in the oceanic circulation patterns brought up nutrients from the abyssal waters. Surviving species were those that coped with the changed conditions and filled the ecological niches left by the extinctions.

 

Gamma ray burst hypothesis

Scientists from the University of Kansas and NASA have suggested that the initial extinctions could have been caused by a gamma ray burst originating from an hypernova within 6,000 light years of Earth (within a nearby arm of the Milky Way Galaxy). A ten-second burst would have stripped the Earth's atmosphere of half of its ozone almost immediately, causing surface-dwelling organisms, including those responsible for planetary photosynthesis, to be exposed to high levels of ultraviolet radiation. This would have killed many species and caused a drop in temperatures. While plausible, there is no unambiguous evidence that such a nearby gamma ray burst has ever actually occurred. One method would be to search the Moon for uneven exposure to gamma rays.

 

Adrian L. Melott estimated that gamma ray bursts from "dangerously close" supernova explosions occur two or more times every billion years, and this has been proposed as the cause of the end-Ordovician extinction.

 

 

 

The gamma ray burst theory sounds very unlikely. Seeing as how a gamma ray burst is the most powerful event in the universe, i wouldn't count on it being the best explaination.

[Widdekind]

Thanks for the info !

 

What if you replace "GRB" with "nearby SN explosion" ?

[jake.com]

Thanks for the info !

 

What if you replace "GRB" with "nearby SN explosion" ?

 

A supernova? Well, being that they are less powerful than a gamma ray burst, i would expect it to be even less likely. The star would have to be much closer, and we would probably still be experiencing the effects today. Personally, i don't buy into the GRB or SN theory. I think climate change would be the most probable answer. But you never know

[D H]

Prof. Richard A. Muller has shown that the Lunar cratering rate actually increased, beginning about 400 Mya*:

 

A big looming question: How much of that graph is just a selection effect? It is based on "155 spherules separated from 1 gram of Apollo 14 soil" (http://www.sciencemag.org/cgi/content/abstract/287/5459/1785). The authors made some sweeping / hand-waving arguments to suggest that this one gram sample of lunar soil is representative of the Moon as a whole.

 

Even worse than a selection effect, is confirmation bias going on here? The authors of this paper have a very non-consensus axe to grind (the Nemesis Hypothesis).

 

For opposing views, see (for example),

 

http://www.sciencemag.org/cgi/content/full/293/5537/1947a

http://elements.geoscienceworld.org/cgi/content/abstract/5/1/23

[Widdekind]

A big looming question: How much of that graph is just a selection effect? It is based on "155 spherules separated from 1 gram of Apollo 14 soil" (http://www.sciencemag.org/cgi/content/abstract/287/5459/1785). The authors made some sweeping / hand-waving arguments to suggest that this one gram sample of lunar soil is representative of the Moon as a whole.

 

Even worse than a selection effect, is confirmation bias going on here? The authors of this paper have a very non-consensus axe to grind (the Nemesis Hypothesis).

 

For opposing views, see (for example),

 

http://www.sciencemag.org/cgi/content/full/293/5537/1947a

http://elements.geoscienceworld.org/cgi/content/abstract/5/1/23

 

Thanks for the links. I wasn't aware of any kind of context for the claims. Yet it still certainly seems worth further investigation -- it doesn't seem to sound like said claims have been categorically disproven.