WJEC GCSE Chemistry 1.4 The Ever-Changing Earth Exam Questions

About WJEC GCSE Chemistry 1.4 The Ever-Changing Earth

The ever-changing Earth covers the structure of our planet and how its atmosphere has changed. You need to describe the layers of the Earth and the theory of plate tectonics, including the evidence that led to its acceptance and what happens at plate boundaries. You must explain how the early atmosphere, mostly from volcanoes, changed into today's atmosphere through condensation forming oceans and photosynthesis. The topic includes the carbon and oxygen cycles, the causes and effects of acid rain and global warming, and laboratory tests for gases. Examiners often ask you to explain how carbon dioxide levels fell and to give the present composition of air.

What you need to know

• Earth's structure The Earth has a solid inner core, liquid outer core, mantle and a thin crust. The crust and upper mantle form tectonic plates that move slowly, driven by convection currents in the mantle.
• Plate tectonics Wegener's idea of continental drift was based on matching coastlines, fossils and rock types but was not accepted until later evidence, such as sea-floor spreading, supported it. At plate boundaries, plates move apart, collide or slide past each other, causing earthquakes and volcanoes.
• Early atmosphere Volcanoes released mainly carbon dioxide and water vapour, with some nitrogen. Water vapour condensed to form oceans; carbon dioxide dissolved in oceans and became locked in carbonate rocks and fossil fuels; photosynthesis by plants added oxygen.
• Today's atmosphere Dry air is about 78% nitrogen, 21% oxygen, about 1% argon (with other noble gases) and about 0.04% carbon dioxide. The carbon and oxygen cycles involve photosynthesis, respiration and combustion.
• Pollution Burning fossil fuels increases carbon dioxide, a greenhouse gas linked to global warming. Sulfur dioxide (and nitrogen oxides) dissolve in rainwater to form acid rain, which damages buildings, trees and aquatic life.
• Gas tests Oxygen relights a glowing splint; hydrogen burns with a squeaky pop; carbon dioxide turns limewater milky (cloudy); chlorine bleaches damp litmus paper.

Common mistakes in 1.4 The Ever-Changing Earth

• Saying the hole in the ozone layer causes global warming. Global warming is caused by greenhouse gases such as carbon dioxide trapping heat.
• Stating that air is mostly oxygen. Air is about 78% nitrogen and 21% oxygen.
• Writing that oxygen relights a splint without saying glowing. The test is that a glowing splint relights.
• Explaining plate movement as caused by earthquakes. Plates move because of convection currents in the mantle; earthquakes are a result of the movement.

Try three 1.4 The Ever-Changing Earth exam-style questions