The upward spike at about 443 million years looks pretty nasty.
Some possible causes:
1. Alien technosignature from long-term visitors of that time period that have long since departed.
2. Advanced terrestrial civilization (aka lizard men/Silurian hypothesis) that was completely wiped away except for their technosignature of rapid heating at 443 million years.
3. Geological/rotational wobble of earth's axis/orbital/revolutional/solar system plane natural process in that time frame.
4. The Russians built a time machine.
IMHO number 3 is most likely (as in 99.999%).