Japan 高校1年 Basic Earth Science
Chapters: 2
1. The Earth
Earth as a planet · Active Earth · Atmosphere and ocean
- Distribution of Oceans and Continents: Drift, Spreading and Plates – In 1912 Alfred Wegener said all continents were once one landmass, Pangaea, surrounded by one ocean, Panthalassa, and that they drifted apart. Matching coastlines, rocks, fossils, glacier deposits and placer gold supported him, but he could not explain the force. Mapping the ocean floor showed ridges, plains and trenches; Harry Hess then proposed sea-floor spreading: new crust forms at mid-ocean ridges and old crust sinks at trenches. This led to plate tectonics: the lithosphere is broken into rigid plates that move on the soft asthenosphere and meet at divergent, convergent and transform boundaries. The Indian plate broke away from the south, moved north, and collided with Asia to raise the Himalayas.
- Composition and Structure of the Atmosphere – The atmosphere is a thick blanket of air held to the Earth by gravity. It is mostly nitrogen (78%) and oxygen (21%), with small amounts of argon, carbon dioxide, ozone, water vapour and dust. It has five layers: troposphere (where weather happens), stratosphere (ozone layer), mesosphere (coldest), thermosphere (ionosphere, very hot) and exosphere (the outer edge). Weather is the state of air for a short time; climate is the average over about 30 years. Both are described by the same elements: temperature, pressure, wind, humidity, clouds and precipitation.
2. Changing Earth
History of the Earth · Earth's environment
- History of the Earth – The universe is about 13.8 billion years old. The Sun and Earth formed from a spinning cloud of gas and dust about 4.6 billion years ago. Earth began hot, then cooled and got oceans. Life started in the sea more than 3.5 billion years ago and filled the air with oxygen. Rock layers and fossils, with the oldest at the bottom, tell us which life and which climate existed at each time. Four big eras (Precambrian, Palaeozoic, Mesozoic, Cenozoic) divide Earth's history, and humans arrived only in the last few seconds of a 24-hour clock.
- Natural Hazards – A natural hazard is a natural event that can harm people and property, such as an earthquake, volcano, landslide, flood, drought or cyclone. It becomes a disaster when it hits people who are not ready. Geological hazards come from inside the Earth; meteorological (weather) hazards come from the air and water. Risk = hazard × vulnerability ÷ capacity to cope, so warning systems, strong buildings and trained people cut the damage.