  Sixty years ago the first observation was published showing solar energetic
particles (SEPs) with a sampling of chemical elements. Thus began study of the
direct products of dynamic physics in the solar corona. As we have progressed
from 4-min sounding-rocket samples to continuous satellite coverage of SEP
events, we have extended the observations to the unusual distribution of
element abundances throughout the periodic table. Small "impulsive" SEP events
from islands of magnetic reconnection on open magnetic-field lines in solar
jets generate huge enhancements in abundances of 3He and of the heaviest
elements. Solar flares involve the same physics but there the SEPs are trapped
on closed loops, expending their energy as heat and light. The larger,
energetic "gradual" SEP events are accelerated at shock waves driven by fast,
wide coronal mass ejections (CMEs). However, these shocks can also reaccelerate
ions from pools of residual suprathermal impulsive ions, and CMEs from jets can
also drive fast shocks, complicating the picture. The underlying element
abundances in SEP events represent the solar corona, which differs from
corresponding abundances in the photosphere as a function of the first
ionization potential (FIP) of the elements, distinguishing low-FIP (<10 eV)
ions from high-FIP neutral atoms as they expand through the chromosphere.
Dependence of SEP acceleration upon A/Q allows best-fit estimation of ion
Q-values and hence of the source plasma temperature of ~1 - 3 MK, derived from
abundances, which correlates with recent measures of temperatures using extreme
ultraviolet emission from jets. New questions arise, however, about the
theoretical basis of correlations of energy-spectral indices with power-laws of
abundances, about the coexistence of mechanisms for enhancements of 3He and of
heavy elements, and about the overall paucity of C in FIP comparisons.
