Changing Atmosphere How Oxygen levels increased on Earth

Changing Atmosphere How Oxygen levels increased on Earth and Carbon dioxide levels decreased

Last Lesson Name the gases present in Earth’s early atmosphere Last Week Name the 3 processes that transport substances in and out of cells. Challenge Write the word equation for photosynthesis Last Topic What unit are forces measured in? How does an object behave if it has balanced forces acting on it? Last Year Which chemical process produces energy for all living things? What are the reactants in this process?

Learning objectives Explain how oxygen first appeared in the atmosphere Explain how carbon dioxide has been removed from the atmosphere over time

Create a timeline explaining how Oxygen levels increased on Earth. Use the following slides to add detail. Time Early Earth 2. 7 Billion Years Ago Additional Notes

2. 7 billion years ago. . . • Algae first produced oxygen about 2. 7 billion years ago and soon after this oxygen appeared in the atmosphere. • Over the next billion years plants evolved and the percentage of oxygen gradually increased to a level that enabled animals to evolve

1. 7 Billion years More and more plants evolved and over the next billion years photosynthesising plants removed much of the carbon dioxide in the atmosphere. The oxygen (produced by photosynthesis) levels gradually increased to a level that enabled animals to evolve.

Use the following slides to create a spider diagram explaining why the Carbon dioxide levels on Earth gradually decreased. Why Carbon dioxide levels decreased

1. Animals eat plants the carbon in plants is transferred and incorporated into structures like shells and skeletons. Over millions of years, as animals died, these structures became covered with sediment and the pressure from this process formed rocks like Limestone. The effect of all this was carbon dioxide levels continued to decrease.

Limestone

Formation of Crude Oil and Gas 2. Some carbon from these animals also formed fossil fuels. 1) Layers of dead sea _____ settle on the seabed. 2) Layers of _____ rock build up on top. 3) The heat and ____ from these rocks, along with the absence of ______, mean that oil and gas are formed over ______ of years. Words – sedimentary, millions, oxygen, creatures, pressure

Formation of Coal

3. Water vapour condensed as the Earth cooled down, and fell as rain. Water fell into the hollows in the crust and formed the oceans. When the oceans formed carbon dioxide dissolved in the water and carbonates were precipitated producing sediments, reducing the amount of carbon dioxide in the atmosphere. Carbon dioxide also reacted with rocks and became trapped in them.

Complete the following questions about our learning Todays lesson Last lesson 1. What has happened to Carbon dioxide levels on Earth? 2. Which process began adding Oxygen to the atmosphere? 3. Name 2 gases that were present in the early atmosphere. 4. Which structures probably created the first atmosphere? 5. What effect did the first oceans have on CO 2 levels? 6. How old is the Earth?