Hi Raoul.

Yes, but the main point:

We are claiming that in reality there was not a totally frozen snowball Earth and that even during the coldest conditions large regions remained ice-free

Dr Dan Condon

http://news.bbc.co.uk/2/hi/uk_news/scotland/1857545.stm

... and here:

[White landscape

The cause of the big freeze is thought to have been a combination of a dimmer Sun - by about 6% - and lower levels of the greenhouse gas carbon dioxide in the atmosphere.

This would have lowered temperatures and allowed the polar icecaps to grow - their spread even accelerating the cooling process as more solar radiation was reflected back into space off the expanding white landscape.

William Hyde from the Texas A&M University, and co-workers, tested such ideas on their coupled climate/ice-sheet computer model - with energy from the Sun and carbon dioxide levels adjusted to what they could have been in the late Proterozoic era.

They found that a "snowball" Earth was quite possible. But by playing with the variables, they also found scenarios that left the planet with an ice-free "oasis" of uncovered ocean.

This, they believe, could have provided a hold-up for lifeforms until volcanic activity had pumped sufficient CO2 into the atmosphere to raise temperatures and defrost the Earth.]

http://news.bbc.co.uk/1/hi/sci/tech/763696.stm

... add this one:

[Detailed analysis of cosmic ray tracks in the meteorites, coupled with an estimate of their age suggests that the intensity of cosmic rays striking our Solar System varies with a period of about 143 million years.

'Good agreement'

The discovery may explain why the dinosaurs were declining before they were wiped out by an asteroid impact 67 million years ago.

About 70 million years ago our Solar System entered the Sagittarius-Carina spiral arm. There is evidence that following this the Earth's global temperature was reduced by about eight degrees Celsius.

Because this was a particularly warm period it was not enough to start a new ice age. It was, however, enough to cause the dinosaurs to decline.

Dr Shaviv says that this timescale agrees with the frequency of major ice ages in the Earth's geological past. It also agrees with our Solar System's passages through the spiral arms.]

http://news.bbc.co.uk/2/hi/science/nature/2163646.stm

---

If you add the basics:

A dimmer younger sun.

Low CO2/greenhouse gases in the atmosphere prior to heavy volcanism.

Our solar system's passage through the Milky Way which could very well be responsible for the abundance or lack of cosmic rays and even disturb our asteroids and comets off their usual paths.

... you can get a good picture and history of our solar system (Mars included) and Earth's climate. It was good to find these articles in one place.

Marcia