The orbit of the planets all seems to align in a plane. The planet's obits have been mapped with only at most a 7° difference to each other. What evidence explains this phenomenon?

It's thought to have arisen from an amorphous cloud of gas and dust in space. The original cloud was spinning, and this spin caused it to flatten out into a disk shape. The sun and planets are believed to have formed out of this disk, which is why, today, the planets still orbit in a single plane around our sun.