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The world is believed to be very warm at this time. Much of the polar ice caps have melted raising sea levels to the point where almost the entire planet was covered with water.
In the atmosphere, the level of oxygen rose sufficiently for the Sun's powerful ultraviolet rays to convert a fraction of the oxygen into ozone in the upper atmosphere.
Ozone is an important substance for it helps to shield living organisms from the harmful effects of ultraviolet light (which is considered by some scientists as one of the most important factors in shortening the lifespan of all living organisms). Without ozone, life, especially for the animals, would probably not have reached out and made the first tentative steps on dry land.
According to computer studies on the development of the ozone layer in prehistoric times, the first animals to ever set foot(?) onto dry land probably appeared at about this time in swampy and heavily protected areas.
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