was dissolved in water. It took a while before this became gaseous and not so toxic to all the lifeforms existing on earth at the time. The glacial ice sheets started to develop and travel down parts of the continents in the Northern Hemisphere. The first time period where glaciation occurred was known as the Gowganda glaciation. The equators were much warmer than the poles, just as is true right now. The history of supercontinents may be different from what you have been taught. You may have heard of Pangaea as the first continent, but this isn't how it all actally began. The first main supercontinent was Vaalbara, existing about 3.6 billion years ago. It broke up to make a supercontinent called Kenorland about 2.8 billion years ago, leading to 4 cratons. These were called the Baltica, Yilgarn, Laurentia, and Kalahari cratons. Still another supercontinent called Nuna or Columbia formed about 2 billion years ago. This broke up to make Rodinia about 1 billion years ago. Pangaea didn't arrive to make up the existing continents until about 335 million years ago.
THE OXYGEN CATASTROPHE The oxygen catastrophe caused a major ecological crisis around the world. Remember that most life forms not only didn't need oxygen, they didn't like it at all. Some oxygen was made into things like iron oxide or rust, while other oxygen atoms went to make other metal oxides. After this happened, oxygen simply had to go somewhere. It went into the atmosphere. When you see large banded areas of rust in rock formations, this is caused by iron oxidation which was rampant on earth. Figure 3A shows a rock that has some of these banded iron oxide layers:
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