Origin of Life on Earth

What do we know about early life on Earth? Evidence from rocks called stromatolites Consist of banded domes of rock Similar to layered mats found in salt marshes today

Stromatolites Large mats found at Shark Bay, Western Australia are considered “living stromatolites”

Cross section of a stromatolite Notice the layers of microbes known as fossilized “mats” of bacteria

What do we know about early life on Earth? Evidence in individual fossilized cells suggest life as early as 3.2-3.5 billion years ago See Fig. 5.2 (text)

What do we know about early life on Earth? Evidence from analysis of ratios of carbon isotopes in ancient rocks (C13, C 12) Rocks older than 3.85 billion years may had organic life

If life existed 3.85 billion years ago… Would we find traces of it? No! Why?

Tree of life as evidence?

Evidence of early life on Earth Stromatolites Fossilized cells Use the tree of life to determine relationships

What was the early Earth like? Water, no land No oxygen present No protection from UV radiation Shallow ponds the home of first life

Early life needs better energy source deep sea vents http://www.ocean.udel.edu/deepsea/level-1/geology/smoker.mov Surface hot springs

Miller-Urey Experiment Used flasks to simulate chemical conditions present on Earth Generated organic molecules…but not enough for life

Where could organic compounds come from? Impacts (asteroids, comets, meteors) Chemical reactions near deep sea vents

What do we have so far? Organic compounds Environment that can produce these compounds What else do we need??

What type of molecule would be best at replication? DNA? RNA?

1980’s discover replicating RNA Cech and colleagues identify that RNA can self-replicate….acts as enzymes Called ribozymes

If it was an “RNA World”

If not “RNA World” then what? DNA…still have the “chicken and egg problem” Proteins were first Double origin, proteins and replication of nucleic acids Clay crystals serve as scaffolding

How can we get to a more “cell-like” model? Need to confine the organic compounds in membranes “pre-cells” formed from Amino acids Lipids mixed with water

Summary of early life…takes many steps Need materials to form “organic soup” Generate more complex molecules (polymers) Membranes formed Natural selection of RNA leads to DNA model

Is this the only idea behind early life on Earth? No What is panspermia?

Evidence to support Panspermia Organic molecules in meteorites Microbes can survive moderate time in space

When did bacteria evolve compared to other cells?

A look at early microbes General characterisitics

Deep Sea vents model early life for microbes

Photosynthesis changed the Earth Organisms could obtain energy from the sunlight Evolved slowly…first just pigments trap uv light Purple and green sulfur bacteria are much like early photosynthetic microbes

Photosynthesis using water Evolved 3.5 billion years ago Earliest fossils resemble modern cyanobacteria (blue-green algae)

Cyanobacteria in Lake Sammamish Sept 1997 Algal bloom of Microcystis aeruginosa