Re: 62 million year extinction cycle


Allan Adler wrote:
There was an article in a recent Science News about the relation between
the motion of the solar system in the Milky Way and mass extinctions on
Earth. As the solar system moves, it bobs up and down relative to the
plane of the Milky Way. That bobbing apparently takes about 62 million
years. When the solar system is on the side closer to Virgo, it is
exposed to more radiation and cosmic rays from Virgo and this is what
they say causes the cycle of mass extinctions on Earth.

This seems awfully surprising to me. What kind of "radiation" are
they claiming changes? I don't see what small amounts of interstellar
material would be blocking. The column density through the Galactic
plane is only of order 10^20 H atoms per cm^2. Is there a reference
to a published article?

Questions:
(1) Where are we presently in the 62 million year cycle? I.e. when was the
last mass extinction of this cycle?

Has there been a mass extinction since the C-T boundary?

(2) How fast are we actually moving towards Virgo and how quickly
should the radiation levels increase as we do?

From my trusty _Astrophysical Quantities_, the Sun's motion towards
Virgo is about 7 km/s. According to NED, Sgr A* has a Galactic
latitude of -0.046 degrees. If the Galactic coordinates correctly
define the plane and the galactocentric distance is 8.5 kpc, that
would put the Sun about 7 pc north of the plane.

As I say, though, I'm suspicious of the whole idea.

.

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