Chemistry 1.4 The Ever-Changing Earth

What are the four main layers of the Earth?

Solid iron inner core

Molten iron outer core

Mantle

Crust

What is the theory of plate tectonics?

The idea that the Earth’s lithosphere is divided into separate parts known as tectonic plates

These plates move over the mantle at a rate of a couple of cm/year, and the process is called continental drift

What was Alfred Wegener’s early theory of continental drift?

The continents all used to be joined together in a supercontinent called Pangea. The Earth’s crust and upper mantle are made up of sections which drifted apart over millions of years.

What occurs at a conservative plate boundary?

Two plates slide past each other

If the movement is sudden and large enough, then there is an earthquake

No volcanoes are found at these boundaries

What occurs at a destructive plate boundary?

Two plates move towards each other

The denser plate is pushed beneath the other and melted

This forms magma, which rises up and leads to the formation of a volcano or an earthquake

The magma then cools, forming igneous rock

What occurs at a constructive plate boundary?

Two plates move away from each other

Magma from the mantle rises up and forms new rock to fill the gap created

If the pressure is high enough, a volcanic eruption may occur

How was the early atmosphere formed?

The intense volcanic activity released gases such as CO2 and water vapour.

What is the present composition of the atmosphere?

78% Nitrogen

21% Oxygen

~0.9% Argon

~0.04% Carbon dioxide

~0.04% Water vapour

What are the causes which lead to the increase of atmospheric concentration of oxygen?

Algae and plants release O2 into the atmosphere during photosynthesis

As plants evolve, the concentration of oxygen gradually increases, enabling animals to evolve and exist

How has carbon dioxide concentration changed in the atmosphere?

Algae and plants decrease the concentration of CO2 in the atmosphere by using CO2 for photosynthesis

Formation of sedimentary rocks and fossil fuels which contain carbon decreases atmospheric CO2

Atmospheric CO2 decreases when it dissolves in the ocean

How has the concentration of ammonia and methane in the atmosphere changed?

As oxygen levels increase:

Ammonia reacts with oxygen to form nitrogen and water

Methane reacts with oxygen to form carbon dioxide and water

Which three processes maintain oxygen and carbon dioxide levels in the atmosphere?

Respiration

Combustion

Photosynthesis

Why has the concentration of CO2 increased considerably in the last 100 years?

Deforestation

Increased burning of fossil fuels

Population growth

What is the major cause of climate change?

Global warming that results from the increase in carbon dioxide and greenhouse gas levels.

What are the potential effects of global climate change?

Destruction of animal habitats that may cause extinction of species

Rising sea level due to the melting of polar ice caps

Increased risk of skin cancer due to more exposure to UV rays

More extreme weather conditions (such as droughts)

What is another byproduct of burning fuels other than CO2?

Sulfur dioxide.

How is acid rain formed?

Sulfur dioxide, released from the burning of fuels, dissolves in rainwater, forming sulfuric acid (also known as acid rain).

What are the effects of acid rain?

Damages buildings and statues made of limestone

Causes corrosion of metal

Reduces the growth of or kills trees and crops

Lowers pH of water in lakes, killing aquatic organisms

What measures are used to address the problems of global warming?

Reduce fossil fuel usage and use renewable sources instead

Encourage eco-friendly travel, recycling, and reusing

Reforestation and creation of more green areas

International deals and targets for emissions between countries

What measure is used to address acid rain?

Sulfur scrubbing - this technique removes 95% of sulfur dioxide from gases released by burning fuels.

Which elements can be found in air?

Nitrogen

Oxygen

Argon

Neon

What is the chemical test to identify oxygen gas?

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

What is the chemical test to identify carbon dioxide?

When bubbled through limewater, carbon dioxide turns limewater cloudy due to the formation of calcium carbonate precipitate.