HISTORY of LIFE

Before Life… Land Environments Earth was molten when it formed about 4.6 billion years ago After 500 million years, a solid crust formed Too much heat for life to exist

Before Life… Atmosphere Gasses in atmosphere came from volcanoes Water vapor, carbon dioxide, methane, ammonia gas, nitrogen, hydrogen, etc. The early atmosphere was anaerobic (it had little or no free oxygen)

Origins of life: Early Ideas Where did the first living things come from?

Aristotle (384 –322 BC) Proposed the theory of spontaneous generation Also called abiogenesis Idea that living things can arise from nonliving matter Idea lasted almost 2000 years

Disproving Spontaneous Generation

1668: Francisco Redi filled six jars with decaying meat. Conditions: Results: 3 jars covered with a lid No maggots 3 open jars Maggots appeared In a jar without a lid, maggots appeared in the meat because adult flies had laid eggs and more adult flies soon appeared

Franciso Redi

1765: Lazzaro Spallanzani boiled nutrient solutions in flasks. Conditions: Results: Nutrient broth placed in flask, heated, then sealed No microbial growth Later, he broke the seals & the soups became cloudy with microbes. Critics said sealed vials did not allow enough air for organisms to survive and that prolonged heating destroyed “life force”

Lazzaro Spallanzani

1861: Louis Pasteur demonstrated that microorganisms are present in the air. Conditions: Results: Nutrient broth placed in s-shaped flask and heated No Microbial growth Nutrient broth placed in s-shaped flask, heated, flask opened Microbial growth S-shaped flask kept microbes out but let air in. Proved microbes only come from other microbes (life from life) - biogenesis

Louis Pasteur

Origins of life: Modern Ideas If life can arise only from pre-existing life, then how did the first life form appear?

Life originated through a series of early chemical events Simple organic molecules simple metabolic pathways emergence of life

Stanley Miller & Harold Urey (1953) First scientists to show that simple organic compounds (macromolecules) could be made from inorganic compounds

Miller & Urey (cont’d) Filled apparatus with water and gases from early atmosphere Electric discharges simulate lightning for energy Resulting mixture contained organic compounds including amino acids.

The First Cells The first cells were anaerobic prokaryotes ( bacteria) Eukaryotic cells first appeared about 1.8 billion years ago when oxygen became a part of Earth’s atmosphere

The Endosymbiont Theory Proposed in 1966 by Lynn Margulis States that a long time ago prokaryotic cells engulfed (took in) other prokaryotic cells. Once inside, the two cells formed a permanent relationship that formed eukaryotic cells

Evidence for the Endosymbiont Theory Mitochondria & Chloroplast Contain their own circular DNA (similar to bacteria) Have their own ribosomes Can reproduce independently of the cell by binary fission (The same way bacteria reproduce!)

HOMEWORK History of Life Notes - Notes Assignment # 1