First we learn that the moon isn’t from where we thought it was from, now the Earth’s origins are being called into question. After years of following the same model for how our planet was formed, some researchers now think they have a new explanation for how Earth got here, and why it’s drier than it should be.
It might seem odd to think of the Earth as a “dry” planet, but based on the prevailing theory for how and where the planet was formed it should actually be much wetter. Water only makes up about one percent of our total mass, you see, and if you look at the previous models for the planet’s formation, that just doesn’t add up.
Why? Well, it all has to do with the “snow line,” the line beyond which ice could condense back when the planets were first forming. According to new research, it was never where we thought it was.
About 4.5 billion years ago our Sun was still surrounded by a mass of gases and other materials. In the old model for how Earth and other planets formed, the material in the disk was fully ionized, causing bits of it to fall into the sun, heating the disk until it ran of stuff to burn and cooled down. While the disk was still in place, the snow line was about 1 billion miles away from the Sun, but as the protoplanetary disk came apart the line moved inward, past where Earth
Article source: http://blastr.com/2012/07/researchers-say-theories.php