I saw a program on the great extinctions on National Geographic Channel yesterday.
A researcher said that the great extinction may be linked to our solar systems movement within our galaxy.
Supposedly, when our galaxy moves through a large gas cloud the friction generates large amounts of radiation.
Our solar system moves from near he surface of the galaxy to towards the inside of the galaxy and then back
towards the surface again etc. This movement has a cycle of 62-64 million years.
When we are near the surface we are more exposed to the radiation.
The position near the the surface of the galaxy apparently correlates with the great extinctions.
The theory is that the radiation weakens life on earth periodically so that any other natural disaster has
more of an impact.
The only extinction that doesn't correlate with the cycle is the Cretaceous–Tertiary extinction, the one that
killed off the dinosaurs.
They say the next great extinction is due in about 10 million years.
However, scientists say we are currently already in the midst of a great extinction, a man-made one.

It all sounds rather credible, your thoughts ?

P.S.
Found an article on it: http://www.dailygalaxy.com/my_weblog/2007/04/cosmic_radiatio.html

There've been a lot of theories like this, ranging from radiation bursts from nearby supernovas to interstellar gas clouds diminishing the amount of sunlight Earth receives as it passes through them. I think it's possible.

Milky Way is the galaxy of which the sun and solar system are a part. It looks like a band of light across the night sky. The Milky Way rotates or moves around the center of the galaxy. The Milky Way galaxy is moving at a speed of around 370 miles per second or around 590 kilometers per second. The sun is moving at a speed of around 150 miles per second or around 240 kilometers per second in a circular orbit around the Milky Way galaxy. It takes 200 - 230 million years to complete one revolution.

Milky Way is the galaxy of which the sun and solar system are a part. It looks like a band of light across the night sky. The Milky Way rotates or moves around the center of the galaxy. The Milky Way galaxy is moving at a speed of around 370 miles per second or around 590 kilometers per second. The sun is moving at a speed of around 150 miles per second or around 240 kilometers per second in a circular orbit around the Milky Way galaxy. It takes 200 - 230 million years to complete one revolution.

No, no, you misunderstand.
The solar system also moves up and down relative to the galaxy disc.

That wobble should not cause any problem as everything moved with it. If not, the gravitational pull without the cetrifugal force would caue the material to drop into the galaxy center or otherwise collected by very large suns long ago.

That wobble should not cause any problem as everything moved with it. If not, the gravitational pull without the cetrifugal force would caue the material to drop into the galaxy center or otherwise collected by very large suns long ago.

Hmm I don't think your seeing the picture here..

Found a picture about it:
http://www.centauri-dreams.org/wp-content/uploads/2007/07/galaxy_radiation.jpg

And a proper article about it:
http://www.centauri-dreams.org/?p=1378

Yes, I see the picture, it is like saying how come the earth does not run in to the moon while going around the sun? While the solar system moves, other stars and clouds should move relatively. Inless gas clouds just hang in there while solar system ploughs through it - that is what you are saying....I do not think that is the case.

Yes, I see the picture, it is like saying how come the earth does not run in to the moon while going around the sun? While the solar system moves, other stars and clouds should move relatively. Inless gas clouds just hang in there while solar system ploughs through it - that is what you are saying....I do not think that is the case.

But.. it is a scientific fact :shrug:
The only question here is whether or not this kick starts the great extinctions.

Do you have a link to that fact? Stuff should not be hanging around unless that dust cloud is above or below us (along the disc) - which is defintely possible. Then it depends on that period and how many cycles the Sol is going through....

The only way to really find out is to take readings of the amounts of radiation that is being absorbed as we are making our way through the cosmos. Unless acurate readings can be done we won't understand what radioactivity s role really is upon the Earth.

Do you have a link to that fact? Stuff should not be hanging around unless that dust cloud is above or below us (along the disc) - which is defintely possible. Then it depends on that period and how many cycles the Sol is going through....

I am on low bandwidth now, I'll get back to you later :)

The only way to really find out is to take readings oif the amounts of radiation that is being absorbed as we are making our way through the cosmos. Unless acurate readings can be done we won't understand what radioactivity s role really is upon the Earth.

I guess we'll find out in 10 million years.. :p

I'm more worried about a super erupting volcano than I'm worried about a meteorite.

http://en.wikipedia.org/wiki/Supervolcano

The Lake Toba eruption plunged the Earth into a volcanic winter, eradicating an estimated 60% of the human population

http://en.wikipedia.org/wiki/Toba_catastrophe_theory

According to the Toba catastrophe theory, 70,000 to 75,000 years ago a supervolcanic event at Lake Toba, on Sumatra, reduced the world's human population to 10,000 or even a mere 1,000 breeding pairs, creating a bottleneck in human evolution.