WJEC Wales Chemistry GCSE 1.4: The ever-changing Earth

Practice flashcards covering the structure of the Earth, tectonic plate theory, atmospheric evolution, global warming, and chemical tests based on WJEC Wales Chemistry GCSE 1.4 notes.

What are the four main layers that make up the structure of the Earth?

The four main layers are the solid iron inner core, the molten iron outer core, the mantle, and the crust.

What is the composition and temperature range of the Earth's inner core?

The inner core is a solid metal ball $2,500\,\text{km}$ wide containing iron and nickel, with a temperature between $5,000 - 6,000\,{}^{\circ}\text{C}$.

Describe the characteristics of the Earth's outer core.

The outer core is over $5,000\,\text{km}$ deep, consists of liquid iron, nickel, sulfur, and oxygen, and has a temperature between $4,000 - 6,000\,{}^{\circ}\text{C}$.

How do the upper and lower sections of the Earth's mantle differ?

The lower mantle nearer the core is a slow-moving liquid at around $3,000\,{}^{\circ}\text{C}$, while the upper mantle nearer the surface is a solid between $1,500 - 3,000\,{}^{\circ}\text{C}$.

What is the thickness range of the Earth's crust?

The crust is the thinnest layer, ranging from as thin as $7\,\text{km}$ to as thick as $80\,\text{km}$.

What components make up the Earth's lithosphere?

The lithosphere consists of the Earth's crust and the upper part of the mantle.

What is the theory of tectonic plates?

The theory that the Earth's lithosphere is divided into separate parts called tectonic plates that move over the mantle at a rate of a couple of centimeters per year.

What causes continental drift?

Continental drift is caused by convection currents in the Earth's mantle, created by the temperature difference between the inner core and the surface.

Who first proposed the tectonic plate theory and the concept of the supercontinent Pangaea?

Alfred Wegener.

What evidence supported Alfred Wegener's theory of continental drift?

Evidence included the jigsaw-like fit of continents, fossils from the same species found on separate continents, and similar patterns of rock formation on both sides of the Atlantic.

What occurs at a destructive or convergent plate boundary?

Two plates move towards each other; the denser plate is pushed beneath the other and melts, forming magma that can create a volcano or cause an earthquake, eventually solidifying into igneous rock.

What characterizes a constructive or divergent plate boundary?

Two plates move away from each other, allowing magma from the mantle to rise and form new rock to fill the gap.

Describe the movement and activity at a conservative plate boundary.

Two plates slide past each other. If movement is sudden and large, an earthquake occurs, but no volcanoes form here.

What was the composition of the Earth's early atmosphere according to volcanic activity theory?

The early atmosphere was mainly $CO_2$ with little or no $O_2$, similar to Mars and Venus today, plus small proportions of methane ($CH_4$) and ammonia ($NH_3$).

How did the oceans form on Earth?

The Earth cooled, which allowed water vapor in the atmosphere to condense into liquid water.

What are the percentages of the main gases in the present atmosphere?

$78\%$ nitrogen, $21\%$ oxygen, $0.9\%$ argon, and $0.04\%$ carbon dioxide.

What is the balanced chemical equation for aerobic respiration?

$$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O$$

What is the balanced chemical equation for photosynthesis?

$$6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$$

How did oxygen levels increase in the atmosphere?

Algae first produced oxygen via photosynthesis about $2.7$ billion years ago, followed by plants evolving over the next billion years.

How did the concentration of carbon dioxide decrease from the early atmosphere?

$CO_2$ decreased through photosynthesis by algae and plants, dissolving in oceans, and the formation of sedimentary rocks and fossil fuels.

Which chemical reaction describes how ammonia was removed as oxygen levels rose?

$$4NH_3 + 3O_2 \rightarrow 2N_2 + 6H_2O$$

Which chemical reaction describes how methane was removed as oxygen levels rose?

$$CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O$$

What three factors have caused carbon dioxide levels to rise in the last 100 years?

Deforestation (burning forests and removing plants), increased burning of fossil fuels, and population growth (increasing respiration and energy demand).

What are the potential effects of global climate change?

Potential effects include destruction of animal habitats, rising sea levels, increased risk of skin cancer from UV rays, and more extreme weather conditions like droughts.

How is acid rain formed?

When fuels containing sulfur are burned, they form sulfur dioxide ($S(s) + O_2(g) \rightarrow SO_2(g)$), which dissolves in rainwater to form sulfuric acid ($H_2SO_4$).

What are the consequences of acid rain?

It damages limestone buildings and statues, corrodes metal, reduces growth or kills trees and crops, and lowers the pH of lakes, which kills fish.

How does the chemical test for oxygen work?

A glowing splint will relight if placed into a test tube containing oxygen gas.

What is the chemical test for carbon dioxide?

When bubbled through limewater, carbon dioxide causes it to go cloudy due to the formation of a precipitate of calcium carbonate.