ideas on the origin of life on earth general biology answer key name___________________
TRANSCRIPT
Early Ideas
• Spontaneous generation - the idea that nonliving material can produce life.Examples:– mud producing fish– grain producing mice– decaying meat producing maggots
Redi’s Experiment
• Effort to disprove spontaneous generation• Decaying meat in uncovered control jars vs.
covered experimental jars.• Results: maggots and flies filled the open jars but
not covered jars. Showed only flies produce flies.
People still didn’t believe it…
• Although Redi disproved spontaneous generation of large organisms, many scientists thought microorganisms must arise spontaneously, probably from a vital force in the air.
Two things must have occurred before life arose:
The formation of simple organic molecules
The organization of those molecules into more complex organic molecules such as proteins, carbohydrates, and nucleic acids.
Earth’s Early Atmosphere
• Contained: – Little oxygen– Mostly water vapor, carbon dioxide gas,
nitrogen gas, methane gas, ammonia gas
• Energy sources - heat from Earth’s formation, lightning, UV radiation
Oparin’s Hypothesis
• Energy from the sun, lightning, and earth’s heat triggered chemical reactions to produce small organic molecules from the substances in the atmosphere. Rain washed these into the oceans, forming a “primordial soup”.
Miller and Urey (1953)
• Set up a simulation of conditions on early earth.
• After 1 week, found they had produced several kinds of amino acids, sugars and other small organic molecules.
• Supported Oparin’s hypothesis.
How did simple organic molecules form complex organic molecules?
• Studies in 1950’s showed that if amino acids are heated without oxygen, they form proteins. A similar process produces ATP and nucleic acids from small molecules.
• Therefore, this may have occurred on early earth in the warm pools of water.
How did these molecules become CELLS?
• Sidney Fox: Protocells could be formed by heating solutions of amino acids.
• Protocell is a large, ordered structure, enclosed by a membrane, that carries out some life activities, such as growth and division.
~LIFE BEGAN!~
• We have found fossils of photosynthetic prokaryotic cells from 3.5 billion years ago. However, these were probably not the first cells.
• Reminder:– prokaryotic:
• example:
– eukaryotic:• examples:
~LIFE BEGAN!~
• We have found fossils of photosynthetic prokaryotic cells from 3.5 billion years ago. However, these were probably not the first cells.
• Reminder:– prokaryotic: simple cell structure, no nucleus
• example: bacteria
– eukaryotic:complex cell structure, has nucleus• examples: protists, fungi, plants, animals
The First Cells
• First cells were probably prokaryotes that evolved from protocells; didn’t need oxygen, used molecules in oceans for food.
• At some point, some cells developed the ability to make their own food– CHEMOSYNTHESIS - making glucose from
inorganic molecules, probably near deep sea vents or in hot springs. No light needed.
And later...
• Some cells developed the ability use light to perform PHOTOSYNTHESIS. This started increasing the amount of oxygen in the atmosphere.
• Some cells developed the ability to use oxygen through respiration.
• Lightning caused some oxygen (O2) to form ozone (O3).
– Protective layer, prevents most UV radiation from sun
– stopped origin of cells; enabled evolution of more complex cells.
Evolution of Eukaryotic Cells
• Lynn Margulis (1960s) - Endosymbiont Theory
– Ancient bacteria may have “taken in” other bacteria, which evolved to become cell structures such as mitochondria and chloroplasts.
– Supporting Evidence:• M & C have their own DNA (similar to
prokaryotes)
• M & C have ribosomes (similar to prokaryotes)
• M & C reproduce independently within cells
And finally...
• Over millions of years, these early cells evolved to the diversity of living things we have on Earth today!!
• This likely involved many, many different mutations over time. Survival was likely determined through natural selection (“survival of the fittest”).
Time From the Present First Records of:
a 4.5 billion years ago origin of the Earth
b *3.8-3.5 billion years ago prokaryotic heterotrophs
c *2.5-3 billion years ago prokaryotic autotrophs, first evidence of photosynthesis
d 1.5 billion years ago unicellular (single celled) eukaryotes
e 650 million years ago multicellular eukaryotes
f 400 million years ago plants invade the land
g 300 million years ago animals invade the land
h 200 million years ago first mammals
i 150 million years ago first dinosaurs
j 100 million years ago last dinosaurs
k *100,000 years ago human development