History of Earth

Formation of the Solar System

• 4.5 billion years ago: Solar system formed from a dense cloud of interstellar gas and dust.
  • Cloud collapsed into a swirling disc of matter.
  • Hydrogen fused into helium, leading to the birth of the Sun.

Formation of the Earth

• Clumps of matter in the disc formed planets and moons.
• Inner planets (like Earth) formed from rocky materials closer to the Sun.
• Young Earth was volcanically active, releasing gases:
  • Hydrogen sulfide, methane, carbon dioxide.

Early Collisions and Atmosphere

• Earth experienced violent collisions:
  • Thea, a Mars-sized planet, collided with Earth, forming the Moon.
• No oceans initially; water existed as gas.
• 3.8 billion years ago: Earth cooled, water condensed, creating the first oceans.

Origin of Life

• 3.7 billion years ago: Earliest forms of life appeared (microscopic organisms).
• Nearly a billion years later, organisms evolved and changed the world.

Formation of Continents

• First continents emerged from ancient oceans (called cratons).
• Formation of the first supercontinent, Valbara.

Evolution of Oxygen Producers

• 2.4 billion years ago: Cyanobacteria evolved to photosynthesize, producing oxygen.
• Resulted in lower CO2 levels, leading to the first ice age.

Continental Movements and Supercontinents

• Continents broke apart and reassembled into Rodinia (largest supercontinent).
• Rodinia broke apart, leading to Pannotia.
• Cambrian Explosion (540-485 million years ago): Explosion of life, evolution of hard-bodied animals.

Mass Extinctions

• 440 million years ago: First mass extinction (Ordovician-Silurian extinction).
• First trees and land animals evolved between 420-350 million years ago.
• 250 million years ago: Last vast supercontinent, Pangea.
  • Experienced the greatest mass extinction (about 90% of species).

Dinosaurs and Evolution

• 240-230 million years ago: First dinosaurs appeared and dominated for 150 million years.
  • Example: Argentinosaurus and T-Rex.
  • Pangea eventually broke apart, forming modern continents.

Chicxulub Impact Event

• 6 million years ago: Asteroid impact near present-day Mexico.
  • Caused climate changes, leading to the extinction of dinosaurs.

Emergence of Mammals and Humans

• 6 million years ago: Earliest known human species, Sahelanthropus.
• 4 million years ago: Early humans began walking upright.
• 800,000 years ago: Discovery of fire, leading to cooking and heat.
• 40,000 to 15,000 years ago: Extinction of other human species (except Homo sapiens).

Agricultural Development

• 10,000 years ago: Emergence of the first farmers, settling down after a nomadic lifestyle.

Industrial Revolution and Population Growth

• 250 years ago: Industrial Revolution transformed societies.
  • Human population:
    • 1804: 1 billion
    • 1927: 2 billion
    • Rapid increase since the 1960s, now over 8 billion.

Current Threats

• Climate change threatens existence of humans and other life forms.
• Rising temperatures, sea levels, and declining biodiversity could lead to another mass extinction event.