The Earth was formed roughly _______________ billion years ago based on ____________ dating. Off-gassing occurred upon the formation of the Earth. As it cooled down to what scientists think was 212 degrees F, water vapor condensed, and oceans formed about __________ billion years ago. The first life we can see in the geologic record appeared as single-cell organisms about ______ billion years ago, just before we see oceans forming. About ___________ billion years ago, life in the oceans produced oxygen that was pumped into the young atmosphere. This life uses the process of _______________ to use the sun and carbon dioxide to respirate oxygen. When water first condensed, it began __________________ cycling of carbon and the water cycle on Earth. A theory called The ____________________ describes Earth covered in a glacial state 2.3 billion years ago, receiving 30