About 4 billion years ago, the Sun was weaker than today,

But the Earth was not much colder -- "How can that be?!" you might say.

People look for answers to this paradox in "BIFs",

The nascence of these iron rocks has led to several tiffs!

Rosing's group had an idea; at first it seemed quite neat-o:

Maybe there were fewer clouds, dropping Earth's albedo.

"Fat chance!" Goldblatt and Zahnle say, new calculations shared:

The max albedo drop (no land): 5 watts per meter squared.

Still others say that deep-sea rocks can't give you CO2

Because of diagenesis and benthic microbe zoo.

The explanation: greenhouse gases way back then were high,

Just begs another question ... if they were, then why?

http://www.nature.com/nature/journal/v464/n7289/full/nature08955.html

http://www.nature.com/nature/journal/v474/n7349/full/nature09959.html

http://www.nature.com/nature/journal/v474/n7349/full/nature09960.html

http://www.nature.com/nature/journal/v474/n7349/full/nature09961.html