Place the following list in order of occurrence from oldest to most recent: 1)appearance of the first oceans on Earth,
2) the Big Bang,
3) contraction of the solar nebula,
4) outgassing of Earth's secondary atmosphere,
5) stellar ignition in our sun,
6) build-up of oxygen in Earth's atmosphere,
7) evolution of photosynthesis.

The nuclear potential that binds protons and neutrons in the nucleus of an atom is often approximated by a square well. imagine a proton conned in an innite square well of length 105 nm, a typical nuclear diameter. calculate the wavelength and energy associated with the photon that is emitted when the proton undergoes a transition from the rst excited state (n 2) to the ground state (n 1). in what region of the electromagnetic spectrum does this wavelength belong?