Week 1 Module Video 1

Overview of Earth's History

• Discussion of the timeline of Earth's history, spanning 4.6 billion years.

• Significant events that shaped life on Earth are highlighted.

Formation of the Universe

• Big Bang occurred 13.7 billion years ago, marking the beginning of the universe.

• Earth and the solar system began formation approximately 4.6 billion years ago.

  • Earth began as molten material and cooled to form a solid crust.

Geological and Biological Insights

• The oldest rocks today date back to 3.8 to 4 billion years ago, formed after heavy bombardment period.

• The oldest signs of life (fossils) discovered in rocks that are about 3.5 to 3.8 billion years old, indicating biological processes:

  • Structures resembling microorganisms found in ancient rocks, suggesting biological origin rather than geological.

Emergence of Cyanobacteria

• Cyanobacteria, or blue-green algae, appeared around 2.5 billion years ago.

  • Photosynthetic capabilities of cyanobacteria led to oxygen accumulation in oceans and atmosphere.

  • Modern-day examples: colonies of individual cyanobacterial cells observed in nature, demonstrating current existence and ecological role.

Evolution of Eukaryotic Cells

• Eukaryotic cells emerged approximately 2 billion years ago.

  • Characterized by organelles such as nuclei and mitochondria.

  • The symbiotic theory suggests that eukaryotic cells originated from the incorporation of aerobic bacteria leading to mitochondria, and later cyanobacteria evolving into chloroplasts.

  • This transition represented increased efficiency in photosynthesis, leading to greater oxygen production.

Snowball Earth Events

• Snowball Earth episodes occurred between 750 and 600 million years ago:

  • Planet experienced dramatic freezing due to continental drift and increased landmass near equator reflecting sunlight.

  • Volcanic activity later contributed to thawing, leading to a warm climate after periods of ice cover.

• This climatic fluctuation allowed diverse forms of life to evolve post ice period.

Cambrian Explosion

• Cambrian explosion occurred around 545 million years ago, showcasing a dramatic increase in biodiversity.

  • Introduction of all major phyla present today.

  • Emergence of complex life forms such as Anomalocaris, a super predator of its time.

  • Example of Hallucigenia and unique organisms showing varied body structures.

Carboniferous Period

• During the Carboniferous period (360 to 330 million years ago), large deposits of coal formed:

  • Appearance of giant dragonflies around 300 million years ago.

Dinosaurs to Modern Life

• Dinosaurs emerged around 230 million years ago.

  • Major extinction event approximately 65 million years ago attributed to a comet strike, leading to a mammalian radiation.

• The evolution of modern humans began around 200,000 years ago, representing a brief period in the long history of life.

Understanding Deep Time

• Concept of deep time illustrates the vastness of Earth's history and helps contextualize geological and biological timelines:

  • Counting exercises demonstrate time scale (e.g., reaching 1 billion takes over 30 years).

• If Earth’s history were condensed to one year:

  • Formation: January 1

  • Oldest rocks: March 4

  • First fossil signs of life: March 28

  • Emergence of cyanobacteria: June 16

  • Eukaryotic algae: Late September

  • Major animal life (Cambrian explosion): November 18

• This visualization emphasizes the uneven pace of life evolution on Earth, showcasing how life began quickly but developed complexity over significant periods.