Lecture Notes on "Origins of Life - NOVA Series"

Introduction

• The series explores how life began on Earth and whether we are alone in the universe.
• Discusses extreme conditions of early Earth and the cosmic events that could have contributed to the origins of life.

Early Earth Conditions

• Earth was formed around 4.5 billion years ago, initially a hostile, molten planet.
• Early Earth was bombarded by asteroids and comets, creating a violent and unstable environment.
• No life existed initially; Earth’s atmosphere was thick with CO2 and lacked oxygen.

Cosmic Contributions to Life

• The theory that meteors and comets delivered essential building blocks of life to Earth.
• Meteorites like the Murchison meteorite contain amino acids, which are vital for life.

Chemical Origins of Life

• Stanley Miller's experiment in the 1950s simulated early Earth conditions and produced amino acids from simple gases and electricity.
• Amino acids are fundamental building blocks of proteins and life.

Extreme Environments and Early Life

• Life possibly began in extreme conditions similar to environments found today, like hydrogen sulfide-rich caves.
• Microbes thrive in hostile environments, suggesting early Earth could support similar life forms.

Evolution of Early Life

• Evidence of early life found in ancient rocks and fossils, e.g., stromatolites in Western Australia.
• Microbial life may have existed as early as 3.8 billion years ago.
• Photosynthesis by cyanobacteria dramatically increased Earth's oxygen levels.

Impact of Photosynthesis on Earth

• Photosynthesis allowed for the production of oxygen, crucial for the evolution of complex life forms.
• Oxygen contributed to the development of an ozone layer, protecting life from harmful UV radiation.
• The transition to an oxygenated atmosphere enabled the evolution of multicellular life.

The Timeline of Life's Evolution

• Life remained microbial and invisible for billions of years.
• Complex life forms, such as plants and animals, evolved only in the last billion years.
• Human evolution occurred within the last second of Earth’s 24-hour metaphorical timeline.

Conclusion

• The lecture explores how life’s chemistry began and evolved under diverse and challenging conditions.
• The transformation from a lifeless rock to a planet teeming with life is a monumental event influenced by both cosmic and terrestrial factors.