Answer to Question 1
The most important source for determining the age of the Solar System is meteorites. Radioactive dating of meteorites yields a range of ages, but there is a fairly precise upper limit many meteorite samples have ages of 4.56 billion years old, and none are older. That figure is widely accepted as the age of the Solar System and is often rounded to 4.6 billion years. The true ages of Earth, the Moon, and Mars are also assumed to be 4.6 billion years, although no rocks from those bodies have yet been found that have remained unaltered for that entire stretch of time.
Answer to Question 2
The solar nebula theory supposes that planets form in the rotating disks of gas and dust around young stars. The evidence is strong that our own planetary system formed in such a disk-shaped cloud around the Sun. When the Sun became luminous enough, the remaining gas and dust were blown away into space, leaving the planets orbiting the Sun.
The dynamic nature of the endomembrane system
Evolution of the gibberellin-DELLA system.
A Microelectromechanical system
The central and peripheral nervous system
Male Reproductive System
How Axis Tilt Affects the Intensity of Solar Radiation