Thought I'd start this thread from a question posed by Carl2 ...

QuoteSo a rather strange question when life first began did the animals or the plants start first, was there ever an excess of oxygen and lack of enough carbon dioxide?

There are several orders of life (the top classification) and it can be ambiguous what is alive (virus' etc.)
If gets more interesting in the domains of life, which are Archaea, Bacteria and Eukaryote.
All plants and animals are eukaryote life and are much further down the evolutionary tree than archaea and bacteria.

The earliest life was about 4 billion years ago, oxygen started building up about 3.5 billion years ago, the great oxygenation event happened about 2.45 billion years ago, eukaryote life evolved about 2.1 billion years ago, multi cellular life about 1.6 billion years ago, plants about 850 million years ago, animals trace back to the Cambrian explosion about 635 million years ago.

So, atmospheric oxygen is due to life but beats plants by about 1-2 billion years and animals came after plants but are the same domain of life. After that you get to kingdoms of life.

Snowcrash,
  Thanks for putting this in, must have taken time and effort, I followed most of it and went from link to link.  it seems we did have an oxygen explosion but very long ago.  I also learned first there earth and after time there was earth and the oceans.
Carl2

And... we are all fish.

I see your "We are all fish" video and raise you a "No such thing as fish" video.  

I'll just put in this link
https://en.wikipedia.org/wiki/Fish
Carl2