• Evolutionary Biology is the study of the history of life forms on earth.
• Evolution refers to the changes in flora and fauna that have occurred over millions of years.
• To understand evolution, we must understand the origin of life and the evolution of the earth, stars, and universe.
• The origin of life and evolution of different life forms on earth can be seen in the context of the evolution of the earth and the universe.
• When we see stars, we are seeing them as they were in the past because of how long it takes their light to reach us. Stellar distances are
measured in light years.
• The light we see from stars has been traveling for millions of years, having started its journey from trillions of kilometers away.
• In contrast, we see objects in our immediate surroundings in the present because light from them reaches us instantly.
• Therefore, when we look at stars, we are in a sense observing the past.
• The origin of life on Earth is a significant event considering the vastness of the universe.
• The universe is enormous at almost 20 billion years old and contains huge galaxies and clusters of galaxies.
• Compared to the universe, Earth is very small.
• The Big Bang theory explains the origin of the universe as a massive a singular explosion that caused the universe to expand and cool,
allowing hydrogen and helium to form and later gases condense into galaxies through gravity.
• Earth formed around 4.5 billion years ago.
• Initially, Earth had no atmosphere. Gasses like water vapor, methane, carbon dioxide and ammonia covered the surface from the molten mass.
• Sun's UV rays split water into hydrogen and oxygen. Hydrogen escaped and oxygen combined with ammonia and methane to form water,
CO2 and others.
• The ozone layer was formed.
• Water vapor condensed and fell as rain, filling depressions to form oceans.
• Life appeared on Earth around 4 billion years ago, around 500 million years after Earth's formation.
• Some scientists believe that life came from outside the earth in the form of units of life called spores through panspermia theory.
• In the past, people thought life arose from decaying organic and rotting matter through spontaneous generation.
• Through experiments, Louis Pasteur demonstrated that life only comes from pre-existing life and disproved spontaneous generation
theory.
• However, Pasteur's experiments did not explain how the first life form originated on earth.
EVOLUTION
ORIGIN OF LIFE
INTRODUCTION
