We know we're at the second half of Earth's life history because life has existed since the very beginning, at least 4 billion years, and it's widely believed that within 1 billion years from now, due to how the Sun will evolve, life will become utterly impossible [1]. Maybe the technology a highly evolved civilization can create could stop that, but given how things are going, that's extremely speculative.
EDIT: correction: by 1 billion years from now, the oceans will be mostly gone and likely animal life will be impossible, but unicelular life will still be possible for another few billion years, according to the linked article... "By 2.8 billion years from now, the surface temperature of the Earth will have reached 422 K (149 °C; 300 °F), even at the poles. At this point, any remaining life will be extinguished due to extreme conditions.". Mind blowing.
EDIT: correction: by 1 billion years from now, the oceans will be mostly gone and likely animal life will be impossible, but unicelular life will still be possible for another few billion years, according to the linked article... "By 2.8 billion years from now, the surface temperature of the Earth will have reached 422 K (149 °C; 300 °F), even at the poles. At this point, any remaining life will be extinguished due to extreme conditions.". Mind blowing.
[1] https://en.wikipedia.org/wiki/Future_of_Earth#Loss_of_oceans