Global Atmosphere Watch was mere scientific interest, but of course, many scientists eventually wondered what effects these trace chemicals could have on the atmosphere, and on life. The GAW's genesis began as far back as the 1950s when the World Meteorological Organization began a programme of monitoring the atmosphere for trace chemicals, and also researching air pollution from a meteorological point of view. They were also responsible for monitoring ozone, establishing the Global Ozone Observing System (GO3OS) in 1957, in the International Geophysical Year. In 1968, the United Nations called for an international conference to address world environmental problems caused by rapid industrialization.
Carbon dioxide in Earth's atmosphere carbonate sediments. The production of free oxygen by cyanobacterial photosynthesis eventually led to the oxygen catastrophe that ended Earth's second atmosphere and brought about the Earth's third atmosphere (the modern atmosphere) 2.4 billion years before the present. Carbon dioxide concentrations dropped from 4,000 parts per million during the Cambrian period about 500 million years ago to as low as 180 parts per million during the Quaternary glaciation of the last two million years. On long timescales, atmospheric concentration is determined by the balance among geochemical processes including organic carbon burial in sediments, silicate rock weathering, and volcanism. The net effect