Life on Earth
From Stardust to Earth: The Start of
Everything
The Start of Everything
• - The universe has fascinated people
throughout history
• - About 13.8 billion years ago: the universe
began
• - In comparison: Dinosaurs extinct ~66 million
years ago
• [Image: Stars and galaxies background]
The Big Bang
• - Theory of the universe’s origin (~13.8 billion
years ago)
• - Edwin Hubble observed galaxies moving
away (expansion)
• - Universe expands like raisins in rising dough
• - Cosmic radiation confirms cooling and
expansion
• [Image: Big Bang illustration]
The Universe Evolves
• - Expansion started from a tiny, dense, hot
point
• - Not an 'explosion' but rapid expansion
• - Particles formed, leading to protons and
neutrons
• - Hydrogen and helium created ~380,000
years later
• [Image: Expanding galaxy visual]
The First Stars
• - Stars formed a few hundred million years
after Big Bang
• - Gravity compressed hydrogen and helium
into stars
• - Fusion created heavier elements
• - Supernovae spread elements across the
universe
• [Image: Star formation / supernova]
The Birth of Earth
• - Earth formed ~4.5 billion years ago from gas
and dust
• - Core heated by radioactive decay
• - Heavier elements sank to the core, lighter to
crust
• - Oldest rocks ~3.8 billion years old
• [Image: Early Earth illustration]
The First Life
• - First life: bacteria (~3.5 billion years ago)
• - Blue-green bacteria performed
photosynthesis
• - Released oxygen, slowly building the
atmosphere
• - Enabled more complex life to evolve
• [Image: Cyanobacteria in water]
Are There More Earths?
• - Earth has all conditions for life
• - Life exists in extreme environments
• - Scientists search for exoplanets with life
potential
• - Universe may hold billions of galaxies and
stars
• [Image: Exoplanet / galaxy illustration]
Summary
• - Universe formed ~13.8 billion years ago (Big
Bang)
• - Stars created heavier elements
• - Earth formed ~4.5 billion years ago
• - First life ~3.5 billion years ago (bacteria)
• - Blue-green bacteria produced oxygen →
complex life
• [Image: Timeline of the universe]