Tracking Down the First Oxygen Users
sciencehabit writes "None of us would be here today if, billions of years ago, a tiny, single-celled organism hadn't started using oxygen to make a living. Researchers don't know exactly when this happened, or why, but a team of scientists has come closer than ever before to finding out. They've identified the earliest known example of aerobic metabolism, the process of using oxygen as fuel. The discovery may even provide clues as to where the oxygen came from in the first place."
Oxygen is not the fuel. It is the oxidant to the fuel to release energy.
We already know the guys who produced the oxygen (or at least we have a good idea), we're interested in the ones who used it.
"My understanding ... is that atmospheric oxygen at levels high enough to sustain oxygen based metabolism came from plants and trees"
Your understanding is quite wrong.
By the time there were "plants and trees" the major part of the biosphere already was oxigen dependant.
The change of the atmosphere from reductive to oxidative predates trees by about two billion years -the start of the proterozoic age is marked about 2.4 billion years ago (with a strong spike around the precambric which still predates trees by about 300 million years).
Cyanobacteria changed the chemistry of the oceans as well. Before oxygen production the oceans contained large quantities of dissolved iron. When oxygen was produced the dissolved iron oxidized and precipitated out as rust. The banded iron formations are a relic of this epoch. It wasn't until the oceans reached equilibrium between oxygen and iron that surplus oxygen was released into the atmosphere.