Topic 3: The Evolution of Life on Earth

Origin of the atmosphere and life Lesson 1

Introduction In this topic you will be studying how the Earth has evolved to support life. The earliest evidence for our atmosphere comes from rocks which were deposited some 3.8 billion years ago in a watery environment.

Early Atmosphere The current scientific view is that the early atmosphere f the Earth consisted of methane (CH 4 ), water vapour (H 2 O), nitrogen (N 2 ), ammonia (NH 3 ) and hydrogen sulfide (H 2 S). These gases are thought to have existed before the evidence shown in the 3.8 million year old rocks.

Early Atmosphere It is not possible to provide absolute measurements of the early Earth’s atmosphere. However there is a degree of credibility as the physical properties of elements found in the 3.8 billion year old rocks are unchanging and the reactions will always follow predictable patterns. We can experiment with this in the lab today.

Origin of Life Charles Darwin ( ) is considered the founder of the modern day theory of evolution. He speculated that life may have started in a warm, phosphate rich pond.

Origin of Life In 1953 a 23 year old, University of Chicago graduate in chemistry named Stanley Miller planned an experiment to reproduce conditions similar to those believed to be on Earth 4 billion years ago.

Origins of life Under the guidance of Harold Urey, Miller began to experiment with a simple apparatus which represented the early Earth.

Origins of life This apparatus was a simulation in which water and gases (representing the Earths early oceans and atmospheres) could be heated and circulated through sparks which simulated lightning.

Origins of life After letting the experiment run for a while, the water began to turn pink and red. Miller analysed the chemicals in the water and discovered an abundance of amino acids. So why does this matter???

Origins of life Amino acids are the building blocks of life. Miller has just performed an experiment that creates amino acids from naturally occurring elements!!

Summary of Urey/Miller Experiment Based on the evidence that Earth’s early atmosphere consisted of methane (CH 4 ), water vapour (H 2 O), nitrogen (N 2 ), ammonia (NH 3 ) and hydrogen sulfide (H 2 S), Urey and Miller set up equipment to try and simulate this early atmosphere. The experiment was performed using two connecting flasks. One flask represented the atmosphere and contained methane, water vapour, nitrogen, ammonia and hydrogen. The other flask represented the oceans and contained boiling water.

Summary of Urey/Miller Experiment continued The gases were circulated between the two flasks and an electrical charge was passed through the “atmosphere” flask to represent lightning. The water representing the ocean was later examined and was found to contain a number of organic compounds including amino acids.

Summary of Urey/Miller Experiment continued Amino acids have a potential to combine and form proteins. Proteins are responsible for the formation, repair and function of all cells in living organisms! It’s important to consider that this is only one scientific perspective and is theory. It’s not proven to create life, and this experiment is currently under investigation as we are not exactly sure what the atmospheric conditions were 4 billion years ago.

A bit to think about In 1997, scientists studying Hale-Bopp Comet discovered that the comet contained: water, ammonia, formaldehyde and hydrogen cyanide which can react to form amino acids! We know that the early Earth was heavily hit by meteorites and asteroids between 4.5 and 3.8 BYA. This was the time life developed…. Could an asteroid collision with Earth have ‘brought’ life to planet Earth?

Homework Read pages Prelim Spotlight Text Update vocab list Complete Dot Points

The Earliest Forms of Life Lesson 2

Early Earth 4 billion years ago the Earth was a very different place than it is today. Not only was Earth different our solar system was different too.

Early Earth The sun was only 70% of its present strength. Earth was spinning much faster and day was only 18 hours long. There was no free oxygen in the atmosphere and only volcanic islands broke the surface of the ocean.

Early Earth How was anything to survive on such an inhospitable planet? To understand this scientists look to current day organisms living in extreme conditions on Earth.

Archaeobacteria ‘Archeo’ means beginning, so these bacteria are thought to be the very first cellular organisms on Earth. They have no nucleus; are ‘prokaryotic’ and are believed to have lived without oxygen present. Unfortunately scientist will never know what these organisms looked like because they did not leave fossilised remains to study.

Present Day Archaeobacteria There are a number of places where microscopic bacteria survive and flourish without oxygen present. This type of environment is called anaerobic (without oxygen). For example, sewage treatment plants and marshes.

Present Day Archaeobacteria Archae have also been found living in a large range of extreme environments; near boiling water surrounding deep-sea vents and hot springs, under glaciers, in highly acidic lakes, in highly alkaline soils and in stomachs of animals

Present Day Archaeobacteria Discovering Archae today, especially near fumorales deep within the ocean, challenge the idea that early Earth was to harsh to support life. This can be viewed as evidence that life could have evolved on a very young and extreme planet Earth. Lets now look at how organisms survive in these extreme conditions

Obtaining Energy Today most cells and organisms live in an oxygen rich environment. Having oxygen present allows them to burn sugars to obtain energy. We call this respiration. When we think of respiration we think of breathing. However this process is much more complex than just breathing.

Respiration There are two types of respiration: Aerobic Respiration: requires the use of oxygen. This is what humans and animals do. Anaerobic Respiration: can take place without oxygen being present. This is what some bacteria are capable of doing. You may be familiar with the term: Fermentation

Aerobic Respiration The equation below is a summary of the chemical reactions involved in aerobic respiration within a cell: If you look carefully you will notice oxygen to be a critical part of this process. Without it, organisms must have obtained energy in other ways

Anaerobic Respiration (fermentation) As we discussed before, anaerobic means without oxygen. Bacteria living in such conditions would have had to generate energy to survive without oxygen present. An example of this is anaerobic fermentation.

Anaerobic Respiration (fermentation) This involves the breaking down of a glucose molecule into two pyruvate molecules, like aerobic respiration but there is further decomposition of these pyruvate molecules which go on to form ethanol.

Chemosynthesis This is another process in which organisms are able to obtain energy in extreme environments. This is a process in which energy is obtained from chemicals present in their surroundings.

Chemosynthesis Organisms use the energy released as chemical bonds are broken in extreme conditions to make carbohydrates from carbon dioxide and water. These organisms are found in areas near black smokers where temperatures can rise above 300 degrees Celsius.

Chemosynthesis Sulfate is stable under normal conditions. The conditions surrounding black smokers superheats water and at these exterme temperatures sulfates are converted into hydrogen sulfide. Chemosynthetic bacteria use the energy released from this conversion as energy instead of the sun.

Homework Complete Dot Points Write up Fermentation Activity 1.15 (pg25) Prelim Spotlight Text in your lab books.

Fermentation Practical Lesson 3

Homework Complete DOT Point 3.7