Planet+Earth+and+Its+Environment,+A+5000+Million+Year+Journey

8.2 Planet Earth and Its Environment – A Five Thousand Million Year Journey Contextual Outline According to currently accepted theory, the Sun formed about 4.7 x 109 years ago from a cloud of gas and dust whose collapse was triggered by a supernova explosion. The condensing gas and dust that went to form the Sun contained all its original elements plus the elements formed during the supernova explosion. Those elements heavier than uranium, from plutonium to californium and beyond, rapidly split into light elements or decayed into uranium and thorium whose half-lives are so long that they have survived in considerable amounts to the present day. In addition to the different elements in the collapsing cloud of gas and dust, there would have been the many and various types of molecules like those found in interstellar space. As the young terrestrial planets formed, they would have consisted of a chaotic mixture of silicates, metals, liquids and gases. The metals sank to the centre of the planets leaving the silicates floating above. This raised the core temperature and forced out the gases that had been trapped inside earlier. These gases formed the early planetary atmosphere. In time, Earth had a surface temperature sufficiently low for liquid water to exist and accumulate in natural depressions, forming the primitive oceans. The hydrologic and lithologic cycles removed methane, ammonia, hydrogen and carbon dioxide from the atmosphere, leaving nitrogen as the dominant gas. The evolution of life and the innovation of photosynthesis produced changes in the atmosphere. The Earth’s atmosphere, lithosphere and hydrosphere have experienced cyclic episodes of cooling and heating and, during this time, the biosphere has been slowly evolving. The present cycles have been established for many millions of years.

This module increases students’ understanding of the historical background and the nature and practice of Earth and Environmental Science.

Assumed Knowledge Domain: knowledge and understanding Refer to the Science Years 7–10 Syllabus for the following: 5.9.1a)discuss current scientific thinking about the origin of the universe 5.9.1b)identify that some types of electromagnetic radiation are used to provide information about the universe 5.9.3a)relate some major features of the universe to theories about the formation of the universe