Key Words Flashcards
What is the atmosphere?
A layer of gas surrounding the earth
What was the early atmosphere composed of?
Mostly carbon dioxide
How did the oceans form?
Water vapour condensing as the earth cooled
How did the amount of carbon dioxide in the atmosphere decrease to today’s levels?
Dissolved in the oceans,photosynthesis,converted to fossil fuel,precipitated as insoluble metal carbonates
When did life start to appear, and what was the impact of this on oxygen in the atmosphere?
About 2.7 billion years ago; amount of atmospheric oxygen increased as it was released in photosynthesis
How has the amount of nitrogen in the atmosphere changed over time?
Increased slowly as it is a very stable molecule
Why can scientists not be sure about the composition of the earths early atmosphere?
It was billions of years ago and evidence is limited
What is the current composition of the atmosphere?
Approximately 80% nitrogen,20% oxygen and trace amounts of other gases such as carbon dioxide,water vapour and noble gases
What is a greenhouse gas?
A gas that traps radiation from the sun
What type of radiation do greenhouse gases absorb?
Longer wavelength infrared radiation
