See also my time-line for an
account of when particular things happened. Thechnically, that's concerned
with positions (in time) while the following is concerned with intervals
(separations in time). Note that there is a natural equivalence
between length scales and time scales, via a factor
of the speed of light; though we relate to the two rather
differently. Likewise, aside from an arguable unit of
something repeated, inversion yields an equivalence between times
and frequencies. Note that the Planck unit of
time, 0.13512e-42 s, is so ludicrously small as to be negligible for any
Over the last 800 k yr, rates of change in atmospheric CO2 concentrations have (except very recently) been at most 30 parts per million over a thousand years – but 1989 to 2006 also saw increases of 30 parts per million.
The Milky Way and Andromeda are expected to pass close to one another in about 2 G yr and, after a second close pass, to fuse together in about 5 G yr – which is roughly how long our Sun is expected to last before turning into a planetary nebula.