  Early dark energy (EDE), introduced at the epoch of matter-radiation equality
to alleviate the Hubble tension, has posed a new coincidence problem: why EDE
appears at matter-radiation equality when their physics are completely
unrelated? To solve this coincidence problem, we propose a new EDE model based
on scalar-tensor gravity with the idea that EDE is triggered by spacetime
dynamics that encodes cosmic radiation-matter transition. Our model can induce
EDE naturally at matter-radiation equality without unnatural parameter tuning.
Compared with other EDE models, a distinguishing feature of ours is that it can
also induce a new energy component during cosmic matter-dark energy transition.
This is testable with low-redshift observations.
