Simulic
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Earth's Atmosphere over 4.5 Billion Years – Changing Composition and the Rise of Life

ChemistryApplied & Practical ChemistryAges 14–15

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Drag the time slider from the early volcanic atmosphere (mostly CO₂ and water vapour, some N₂, almost no O₂) to today's air (N₂ 78 %, O₂ 21 %, Ar 0.93 %, CO₂ about 0.04 %). Watch water vapour condense to form the oceans, CO₂ dissolve and become locked in carbonate rocks and fossil fuels, cyanobacteria, algae and plants raise O₂ (the Great Oxidation Event) and the ozone layer form. A live pie chart and timeline graph update as you go, and a table names the process changing each gas.

Lesson: Evolution of Earth's atmosphere: the early atmosphere, formation of the oceans, photosynthesis and the rise of oxygen, carbon locked in carbonate rocks and fossil fuels

What it shows

Earth's first atmosphere came from volcanoes: mostly carbon dioxide and water vapour, with some nitrogen and small amounts of methane and ammonia, and almost no oxygen. As the planet cooled, water vapour condensed into oceans, which dissolved CO₂ and locked it into carbonate sediments. About 2.7 billion years ago cyanobacteria began photosynthesis; once dissolved iron was used up, oxygen built up in the air and an ozone layer formed. Plants later locked carbon into coal and other fossil fuels, leaving today's nitrogen–oxygen atmosphere. Early values are scientific estimates.

How to use

Drag Time, press Play to run through Earth's history, or use the milestone buttons such as Great Oxidation Event and Today. You can also drag along the timeline graph. Untick Include water vapour to see dry air, and switch Scale to Logarithmic to see trace gases. Press Record to add the current composition to the table and compare times.

Parameters you can change

  • Time (before present) 0–4500 million years ago
  • Include water vapour in the composition
  • Graph scale Linear (0–100 %), Logarithmic (shows trace gases)
  • Play speed 50–500 million years per second

Questions to explore

  1. Which two processes removed most of the carbon dioxide from the early atmosphere, and where is that carbon stored today?
  2. Why did oxygen stay close to zero for hundreds of millions of years after cyanobacteria began photosynthesis?
  3. How did the rise of oxygen make it possible for life to colonise the land?

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