  Magnetic reconnection is a sporadic process responsible for energy release in
space and laboratory plasmas. It is believed that the tearing mode instability
may be responsible for the onset of reconnection in the magnetotail. However,
due to its elusive nature, there is an absence of in-situ observations of the
tearing instability prior to magnetic reconnection in our nearest natural
plasma laboratory. Using neural network outlier detection methods in
conjunction with Cluster spacecraft data, we find unique electron pitch angle
distributions that are consistent with simulation predictions of the tearing
instability and the subsequent evolution of plasma electrons and reconnection.
We confirm that the events identified via our neural network outlier method are
well above the tearing stability threshold based on the criterion detailed in
this paper. We find signatures of magnetic reconnection minutes after the
majority of tearing observations. Our analysis of the tearing instability
provides new insights into the fundamental understanding of the mechanism
responsible for reconnection, a process that is ubiquitous in different
astrophysical plasma regimes across the universe and in laboratory experiments
on Earth.
