IB Biology A1.1 Notes

Now that you have learned about the properties of water, you can appreciate how vital it is to life on Earth. In fact, 70% of our bodies and 70% of the Earth's surface are composed of water, highlighting its importance to life. However, the Earth did not always have this much water.

You are expected to understand how these water levels formed on Earth. To understand this, let's start from the beginning:

1. Approximately 4.6 billion years ago, part of a molecular gas and dust cloud collapsed on itself.
2. It begun to rotate faster during its collapse and form a hot protostar center and colder protoplanetary disc.
3. Gravity condensed the center into the Sun and dust and gas in the disc into hundreds of protoplanets.
4. Many of these were ejected, destroyed or collided and merged to form the early planets of the Solar System. 
5. Solar winds and the high temperatures of the inner Solar System removed hydrogen and helium, forming the rocky planets of Mercury to Mars.
6. Further planets were far enough away that solar winds and low temperatures allowed gases to remain and expand, forming the gas giants of Jupiter to Uranus.
7. Leftover debris congregated in asteroid belts.