Oxygen before animals?

Animals evolved about 600 million years ago and late in Earth’s history. Their late evolution and the fact that oxygen is central for animal respiration led to the idea that animal evolution corresponded with an increase in the atmospheric oxygen concentrations. However, recent studies from samples from the Xiamaling Formation in China showed that a deep ocean 1.4 billion years ago contained at least 4% of modern oxygen concentrations, which is enough for animals to exist. This shows that over 800 million years went by before the first animals appeared on Earth. Some researchers said that animals such as sponges and worms are capable of managing with less than 4% oxygen. Since the results from different studies differed so much, researchers are questioning why animals rise so late in Earth’s history and considering the fact that perhaps, the oxygen rise had less to do with the animal revolution than they presumed.