The Origin and History of Life

What is a theory? An explanation widely accepted and supported by evidence Remember- –Theories are just as important or accepted as Laws

In a nutshell... 1.Simple organic molecules must have formed from something. 2.These simple organic molecules became organized into complex organic molecules like proteins and nucleic acids which led the way to further development. 3.Anaerobic organisms  chemosynthetic prokaryotes  photosynthetic prokaryotes (Oxygen)  aerobic prokaryotes  eukaryotes (endosymbiotic theory)

What happened before life on Earth? Atmosphere was probably composed of water vapor, carbon dioxide, nitrogen, and perhaps methane and ammonia.

How did life begin? Some of the different viewpoints –Divine origins –Spontaneous Generation- Redi, Pasteur –Primordial Soup- Oparin, Miller/ Urey –Meteorites –RNA World

Spontaneous Generation Spontaneous Generation- the idea that nonliving material can produce life (Meat - Maggots) –Redi (1668) - showed that large organisms do not arise spontaneously –Pasteur (1850s)- showed that microorganisms do not generate spontaneously

Redi’s Experiment

Pasteur’s Experiment

Oparin’s Hypothesis in the 1930s Energy from the sun, lightning, and Earth’s heat triggered chemical reactions to produce small organic molecules from the substances present in the atmosphere. Then rain washed the molecules into the ocean to form “primordial soup”.

Primordial Soup

Oparin’s Hypothesis Tested by Miller and Urey in 1953 Hydrogen + Methane + Ammonia + water vapor + electricity = amino acids and sugars

Miller and Urey’s Experiment

Other Ideas… Proteins and other first organic compounds came from outer space (meteorite idea) RNA came first

Other Ideas… Divine Intervention

But what about cells?? 3.5 billion years ago- first prokaryotic cell found in the fossil record 1st prokaryote came from protocell –Protocell: large, ordered membrane, that carries out some life activities (Fox-heated amino acids = formed chains which formed “cells”)

Endosymbiosis One organism lives within the body of another Both benefit from the relationship Early mitochondria and chloroplasts were once prokaryotic cells taken up by larger prokaryotes Smaller cell lived inside larger cell

Endosymbiosis Cell takes up mitochondria = energy gain in form of ATP Cell takes up chloroplast = gains the ability of photosynthesis

Evidence Mitochondria and chloroplast have their own DNA and ribosomes They can both copy themselves Both about the same size as prokaryotes Both have circular DNA, like a prokaryote

Cell Growth and Diversity Over time, cells began to reproduce sexually Led to diversity Unicellular to multicellular

Radiation of Multicellular Life As multicellular organisms evolved, the new environment produced new ecological opportunities

Life Moved to Land Multicellular = Paleozoic era (544 million years ago) –Cambrian explosion led to a huge diversity of animal species –All life was in ocean Life then moved to land –Plants increased