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Fraser
2007-Mar-23, 09:32 PM
Planetary geologists propose that our planet once had periods of extreme global freezing nicknamed the "Snowball Earth" eras. During these periods, they supposed, the planet's temperatures went so low that the oceans froze, and everything was covered in ice. ...

Read the full blog entry (http://www.universetoday.com/2007/03/23/snowball-earth-probably-had-warm-spots/)

JonClarke
2007-Mar-24, 01:46 AM
In other words, not a snowball.

Ronald Brak
2007-Mar-24, 01:56 AM
Interesting to think what this might mean for a planet closer to the far edge of the habitable zone. Will they be likely to often enter snowball periods which would end when greenhouse gases from volcanism build up? Is that what happened to Hoth in the Empire Strikes Back? (Note to Star Wars enthusists: This is a retorical question.)

JonClarke
2007-Mar-24, 10:49 AM
Quite possibly.

GOURDHEAD
2007-Mar-25, 11:08 AM
....the planet's temperatures went so low that the oceans froze, and everything was covered in ice. ...Nothing a ten mile across asteroid collision couldn't fix. Look Ma! No scars.

trinitree88
2007-Mar-25, 10:38 PM
Nothing a ten mile across asteroid collision couldn't fix. Look Ma! No scars.

Gourdhead. I think a ten mile wide asteroid would not only melt the ocean, but leave a scar in the mud. The Barringer crater baby was about ~150 feet, or 50 meters across.
http://www.barringercrater.com/science/

Ronald Brak
2007-Mar-26, 12:58 AM
I think a ten mile wide asteroid would not only melt the ocean, but leave a scar in the mud. The Barringer crater baby was about ~150 feet, or 50 meters across.

...and made a hole almost a mile across.

JonClarke
2007-Mar-26, 11:39 AM
There was at least one giant impact during this period, the Acraman event. Unfortunately it hit between two glacials, after the Marinoan and the Wilpenan.

Jon

GOURDHEAD
2007-Mar-26, 01:27 PM
My wild guess of no scars is based on the asteroid losing velocity in the thicker colder atmosphere and then hitting an ice cover of several miles thickness in a temperate zone resting on a couple miles of liquid water. I agree that scars could have been left depending on where it hit. My fantasy is focussed on melting the ice not gouging the Earth.

If this happened, unlikely as it would be, how fast would the Earth return to its mean (over the epochs) temperature?

John Mendenhall
2007-Mar-26, 02:55 PM
If this happened, unlikely as it would be, how fast would the Earth return to its mean (over the epochs) temperature?

After the initial heating from a large impact, speculation is that Earth would enter a global winter due to sunlight blocking. I don't think there's enough initial heating to melt global ice sheets; maybe it would just be a hiccup in a snowball Earth epoch.

But what if the impact produces huge followup volcanic activity, like the Siberian and Deccan traps? That might bring the Earth out of the deep freeze, although not quickly.

JonClarke
2007-Mar-26, 11:56 PM
After the initial heating from a large impact, speculation is that Earth would enter a global winter due to sunlight blocking. I don't think there's enough initial heating to melt global ice sheets; maybe it would just be a hiccup in a snowball Earth epoch.

But what if the impact produces huge followup volcanic activity, like the Siberian and Deccan traps? That might bring the Earth out of the deep freeze, although not quickly.

You are quite correct. The initial response to a large impact would be more cooling because of increase in cloud cover.

As for post impact volcanism, I think that is now largely discounted.

Jon

Nick4
2007-Jun-07, 04:25 AM
maybe the hot spots were from volcanic activity