what would happen to the planet if all oxygen breathing organisms became extinct and only plants remained on the earth

All the power plants and various ways we get electricity would keep going, although anything controlled with artificial intelligence might automatically switch off.

Before that happens, most of our pets will die because they can't get out of the house. Some of those that can, will adapt to the great outdoors and become feral. Farm animals would break out of their fields as electric fences would no longer be working. A lot of those animals that can't escape would soon die

The nuclear power plants within a month or two will meltdown, and this will expose the Earth to a lot of radiation. There will be explosions at oil refineries, and fires will break out. There will be floods in subways as we have machines that pump out millions of gallons of water every day. In fact, because flood gates in some cities won't be operational, many of our metropolises will soon turn very soggy. Any dry cities located near deserts will soon be covered with sand. All this will happen in the first two or three months.

4. weeds will start spreading around cities, while vines will be growing up the sides of buildings. Cities will look a lot greener as plant-life flourishes. Indoors, mold will grow on the walls, and all houses will be overrun with insects, mites, and mice.

5. At about 20 years, 75 percent of the world's cities will be completely overgrown with plant life. Many buildings will be crumbling, and animals that survived will be in vast numbers. Bridges will have rusted; cars will, too, as vines wrap around them.

6. After 50 years, we hear the croak of what sounds like someone speaking English. It is the last words of a dying parrot, the last living thing to use what was once human language.

7. After 100 years, you can just about make out the skeleton of a car, almost unrecognizable due to corrosion. Washington DC is a swamp, and the White House has almost crumbled. Insects and mites have eaten almost all of our great works of art.

8. A hundred years after that, and most of our great buildings have collapsed. Earthquakes and hurricanes have transformed the surface of the Earth. Many of the oldest structures still remain intact. Stonehenge still sits amid long grass, where sparrows busily go about their day just as they did when humans were still around.

9. After 500 years, cities such as Rio de Janeiro look like rainforests. 500 years after that, and almost all cities have been overrun with vegetation.