Linking Mass Extinctions To the Sun's Journey In the Milky Way

schwit1 writes "In a paper published today on the Los Alamos astro-ph preprint service, astronomers propose that as many as eleven past extinction events can be linked to the Sun's passage through the spiral arms of the Milky Way. (You can download the paper here [pdf].) From the paper: 'A correlation was found between the times at which the Sun crosses the spiral arms and six known mass extinction events. Furthermore, we identify five additional historical mass extinction events that might be explained by the motion of the Sun around our Galaxy. These five additional significant drops in marine genera that we find include significant reductions in diversity at 415, 322, 300, 145 and 33 Myr ago. Our simulations indicate that the Sun has spent ~60% of its time passing through our Galaxy's various spiral arms.'"

Comments

Re:Oort cloud?

[symbolset]

In the paper this is diiscussed as one possible explanation.

Such encounters would not pose a di- rect hazard to life on Earth by changing the orbit of the Earth around the Sun, but could pose a haz- ard by disturbing the Oort Cloud

Explanation is elsewhere

[monatomic]

http://news.nationalgeographic.com/news/2007/04/070420-extinctions.html Other researchers found that time periods Earth is exposed to large amounts of cosmic rays is correlated with mass extinction events. This is a possible explanation.

Re:spiral arms?

[bill_mcgonigle]

Yeah, it wasn't clear from TFS or TFA what they were talking about, but further down in the discussion:

TL;DR: the Sun orbits the galaxy faster than the spiral arms, and when the solar system passes through gas clouds in the spiral arms, that can send more Ort-cloud comets at the Earth.

The motion of the spiral arms around the cen-
tre of the Galaxy is somewhat slower than that of the
stars that make up the galaxy, which means that, as
the Sun orbits the centre of the Galaxy, it follows
a path that takes it through the spiral arms every
few tens of millions of years. In the spiral arm envi-
ronment, the Solar System is exposed to a far more
hazardous and busy regime than in the inter-arm re-
gions (our current location). The Earth could be
relatively close to a star when its life comes to an
end in a supernova explosion { which could certainly
pose problems for life, although such supernovae are
relatively rare, and the odds of the Earth being suf-
ciently close to one for life to be exterminated en-
tirely are low, even within a spiral arm (Beech 2011).
At the same time, close encounters between the Sun
and neighbouring stars become more frequent, as do
encounters between the Sun and giant gas clouds
(see Fig. 2). Such encounters would not pose a di-
rect hazard to life on Earth by changing the orbit
of the Earth around the Sun, but could pose a haz-
ard by disturbing the Oort Cloud (Porto de Mello et
al. 2009), a vast cloud of comets (Oort 1950) which
stretches to a distance of at least 100 000 AU from
the Sun. The Oort Cloud is thought to contain tril-
lions of cometary nuclei, left over from the formation
of the Solar system, which are only tenuously grav-
itationally bound to the Sun (the outer members of
the cloud are around halfway to the nearest star).
An encounter with a passing star or distant molec-
ular cloud can be enough to deflect an Oort cloud
comet, throwing it onto a new orbit that will bring
it into the inner Solar system { where it can pose a
threat to the Earth. The closer the star approaches
to the Sun, or the more massive it is (or both), the
more comets it will scatter inwards, and therefore
the more likely it will be that one of those in-falling
comets will hit the Earth.

Re:What we need to know...

[MatthiasF]

We are actually passing through a minor one right now, called the Orion Spur.

http://en.wikipedia.org/wiki/File:Artist's_impression_of_the_Milky_Way_(updated_-_annotated).jpg

Re:Oort cloud?

[dkf]

No mention of Shock waves, or even a hint of what might cause such shock, or how such shock could be transmitted in the vacuum of space.

Via the interstellar medium, of course. It's pretty tenuous, but most certainly is capable of sustaining phenomena like shock waves. Which isn't to say that that's necessarily the particular process that is dominant in the galactic arms; it could also be something relating to magnetism, as the physics of a flowing magnetically-coupled medium is viciously difficult to work with (i.e., highly non-linear). And I've got no idea what happens at the phase change boundaries between the parts of the ISM which are plasmas and the parts which are conventional (tenuous) gasses; phase changes can do "interesting" things.

As for what's powering it all, you've got some exceptionally powerful energy sources out there. Black holes in particular can pump vast amounts of energy into the surrounding volume of space. The stellar wind from very high mass stars would be another interesting source.