8.4 Life, Chemical Evolution and Climate Change 8.5 Cosmic Influences on the Evolution of Earth

Stromatolites

• a calcareous mound built up of layers of lime-secreting cyanobacteria and trapped sediment

Atmosphere

• Lacked oxygen which would allow for amino acid production 

• Evolution of Cyanobacteria: Helped perform photosynthesis → Taking in CO₂and producing O₂ 

  • Originally oxygen would react with the crust not allowing it to build up, but it did enveutally 

• Free oxygen allowed for the formation of the ozone layer → Protected earth from UV rays 

  • Life evolved from ocean to land due to the ozone

Theory

• Life began in nutrient rich seas and evolved from there, thrived in high temps 

• LIfe begun on mars and then came to earth via meteorites 

• LUCA: Modern genetic and genomic studies show all life shares a common ancestor

  • Most of Earth’s biodiversity is microbial 

Anthropocene

Geological epoch where humans dominantly influence earth’s ecosystem and atmosphere

Craters

Caused by the impact of celestial objects onto another's surface

• Earth lacks visible craters due to it being geologically active, tectonic plate movement reshapes earths surface to erase any craters

Notable Impacts

• Tunguska Event: Serbia

  • Stony projectile (~60 m diameter) exploded 8 km above ground.

  • Flattened ~1,000 km² of forest, killed animals, injured people.

  • No crater formed because the object disintegrated in the atmosphere.

  • Explosion equivalent to 10-megaton nuclear bomb.

• Chelyabinsk Event: Russia 

  • Smaller projectile (~20 m) exploded 21 km above ground.

  • Burst brighter than the Sun, broke windows, hundreds injured.

• Meteor Crater: Arizona

  • Iron projectile (~40 m) formed a crater ~1 mile across.

  • One of the few relatively intact impact craters on Earth.

Mass Extinction

• Cretaceous-Paleogene (K-Pg) Extinction (65 million years ago)

  • The impactor struck the shallow sea in the Yucatán Peninsula, Mexico, creating the Chicxulub crater (~200 km wide).

• Evidence of it being a crater from an astronomical object

  • IN this crater there is Global iridium-rich sediment layer, rare on Earth but common in asteroids.

  • Minerals indicating high temperatures and pressures.

impact of K-Pg

• Ended the age of dinosaurs and many other species.

  • Mammals subsequently diversified and evolved.

  • Survival also depends on surviving random global catastrophes not just adaptation 

• 100 trillion tons of dust blocked sunlight → months of cold and darkness.

• Death of sunlight-dependent plants → collapse of food chains.

• Worldwide fires and acidic rain.