system
Given the following post, respond as if you're commenting on Reddit:
human
What caused the massive spike in oxygen content in Earth's atmosphere 300 Million years ago?
gpt
The success of land plants as forests of tree-like vascular plants led to the spike in atmospheric O2 in the Carboniferous Period. This and the rapid burial of plant material in swamps that became world wide coal measures. The fossil evidence for this is the rise of very large insects, such as *meganeura* a dragonfly the size of a small bird, allowed because the capacity of the tubes that insects use to breathe was limited but could be offset for larger individuals by the higher O2 concentration.