Early Earth Conditions

Origin of Life Beliefs

• 1. Spontaneous Generation- idea that nonliving material can produce life

ex. People believed decaying meat produced maggots ex. Mice suddenly appearing in sacks of grain• 1668- Francesco Redi (Italian physician)

disproved spon. gen.

Redi’s Spontaneous Generation Experiment

Disproving spontaneous generation

• Redi disproving spon. Gen. allowed people to believe in biogenesis (idea that living organisms come from other living organisms)

The Modern Ideas1. Meteorites

a. Life started when a meteorite containing organic matter collided with the Earth

b. Could explain how organic molecules that are necessary for cell formation arrived on Earth and entered the oceans

2. Divine Origins (Intelligent Design)

a. Many major religions teach that life was created by supreme being

1. Explain it as life could not have been created without the intervention of a divine force

The Modern Ideas (continued)3. Primordial Soup

a. Idea that Earth’s ancient atmosphere probably contained nitrogen, methane, ammonia, and carbon dioxide

1. Energy from sun, volcanoes, and lightning fueled chemical reactions among these gases, which combined into small organic molecules like amino acids

2. Rain washed these molecules into the oceans making…primordial soup!

b. Harold Urey and Stanley Miller provided evidence to support this.

Early Earth Conditions• According to the geologic time scale it’s believed

that the Earth formed approximately 4.6 billion years ago

• SO HOT!!! Due to radiation (left over from big bang), volcanoes, friction from colliding meteorites

• All eruptions of volcanoes made all gases present (CO2, N2, H2, CO, methane, and ammonia)

• H2O is present as water vapor b/c it’s so hot!!

Early Earth Conditions• About 3.5 byo (billion years ago) earth started to

cool and H2O condensed to form liquid H2O

*Rock evidence shows 1st signs of life (from fossils) was around 3.5 byo

• Led to millions of years of rainstorms to form the oceans

• Helps support Miller/Urey experiment

How do scientists believe life began?

• SO HOW DID LIFE BEGIN ON EARTH??• TO GET LIFE YOU NEED TO FORM ORGANIC

MOLECULES (CONTAIN CARBON)!!!

Formation of Organic Molecules

• 1. Believed early atmosphere contained little to none free O2

• 2. Most atmosphere was made of (water vapor, carbon dioxide gas, nitrogen gas, methane gas, ammonia, hydrogen gas, and carbon monoxide) Key point- No Free Oxygen Yet!!• *1938 Alexander Oparin proposed Primordial

Soup Theory (says life began in the oceans)

Primordial Soup Theory• Oparin said energy from sun, lightning, &

Earth’s heat triggered chem rxns. to produce small organic molecules from substances present in Earth’s atmosphere

• Then rain washed these molecules into oceans making this primordial soup

• 1953 Stanley Miller/Harold Urey (American Scientists) wanted to test Oparin’s theory by simulating Earth’s early conditions in the lab

Miller/Urey Experiment• 1. Mix water vapor (steam) w/ ammonia, methane gas, and hydrogen gas• 2. Send electric current (simulates lighting) through it• 3. Cool gases- which produces a liquid that simulates rain• 4. Collect liquid in flask• 5. Results- found several kinds of amino acids, sugars, nucleotides & other organic molecules that supported Oparin’s hypothesis

So, how do organic molecules lead to cells??

• Evolution of Cells• 1st cells- protocells- large structure w/ a

membrane that contains the primordial soup & carries out cell division

• Believed that prokaryotes (bacteria) evolved from protocells

*Remember there is no free O2 present yet

Evolution of Cells Timeline

3.5 byo- So, 1st prokaryotes were non-photosynthetic bacteria (heterotrophic anaerobes) that ate primordial soup or others did chemosynthesis & made own glucose

4.5 byo 3.5 byo 2.5 byo 1.5 byo 0.5 byo

Evolution of Cells Timeline

• 3.2 byo- 1st photosynthesizing prokaryotes • (autotrophic bacteria) evolved • which released O2 in the atmosphere

4.5 byo 3.5 byo 2.5 byo 1.5 byo 0.5 byo

Evolution of Cells Timeline

• 2.0 byo-2 major events occurred: Due to • the accumulation of oxygen the 1st • eukaryotic cells evolved…lightning • striking the O2 would have formed O3 • (ozone) and allowed more complex • organisms (eukaryotes) to thrive•

4.5 byo 3.5 byo 2.5 byo 1.5 byo 0.5 byo

Endosymbiont Theory• *Believed that eukaryotes evolved from

prokaryotes• 1960s- Lynn Margulis proposed this theory• She said eukaryotes evolved by symbiotic

relationships w/ prokaryotes

Evidence to support Margulis’ beliefs

• Cyanobacteria & chloroplasts (contain DNA & ribosomes) look similar & can both do photosynthesis

• Some bacteria & mitochondria (contain DNA & ribosomes) look similar