1. Topic 6
Origins of Life

2. theories of the origin of life

3. What are we learning today?
Benchmarks
SC.912.L.15.8 – Describe the scientific explanations of the origin of life on Earth.
Learning Objectives
I will describe scientific explanations of the origin of life on Earth.
I will identify situations or conditions contributing to the origin of life on Earth.

4. What is the essential question?
Scientists explain that that life arose from nonlife billions of years ago through the theory of abiogenesis. Could life arise from nonlife today? Explain.
Probably not. The same conditions no longer exist on Earth. The oxygen in the atmosphere would likely react with and destroy any new kinds of organic molecules or they would be consumed by bacteria and molds.

7. What conditions make Earth unique?
Only planet known to sustain life.
Several conditions make Earth able to sustain life as we know it.
presence of liquid water
moderate temperature range
free oxygen in the atmosphere
adequate sunlight
no toxic substances in the atmosphere
absence of lethal radiation

8. What was earth like?
Earth’s early atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water.
Volcanic activity probably formed it.
Released great amounts of water vapor that later condensed to form oceans.
Released CO2 that warms the atmosphere by absorbing outgoing heat. How did that affect the temperature?
This early atmosphere lacked oxygen, so it could not support life as we know it today.
WHERE DID LIFE BEGIN?
HOW DID LIFE BEGIN?
WHAT DID IT LOOK LIKE? SO MANY QUESTIONS!!!

9. where did life Begin? Fossil Evidence Primordial Soup Theory
Fossil evidence indicates that life on Earth appeared about 3.5 billion years ago in the oceans
Provided protection from UV radiation
Allowed multidirectional movement
Served as a medium for essential chemical reactions.
Anaerobic prokaryotes
Proposed by Alexander Oparin and John Haldane.
Early atmosphere contain NH3, CO2, H2O, H2, and CH4
At high temperatures, these gases may have formed single organic compounds.
When Earth cooled and water vapor condensed, these simple organic compounds would have collected in lakes and oceans.
Overtime. these compounds could have entered complex chemical reactions, fueled by energy from ultraviolet radiation, volcanic eruptions, and lighting.

10. Abiogenesis vs. Biogenesis
Abiogenesis or spontaneous generation states that life can arise from nonliving things
Oparin reasoned that O2 prevents the synthesis of certain organic compounds that are necessary building blocks for the evolution of life
Oparin proposed that the "spontaneous generation of life" did in fact occur once, but was now impossible because the conditions found on the early Earth had changed
Oparin argued that a "primeval soup" of organic molecules could be created in an oxygen-less atmosphere.
Biogenesis states that every living thing came from a pre-existing living thing.
In 1668 Francesco Redi, proved that no maggots appeared in meat when flies were prevented from laying eggs.
In 1768, Lazzaro Spallanzani demonstrated that microbes were present in the air, and could be killed by boiling.
In 1861, Louis Pasteur performed a series of experiments which demonstrated that organisms such as bacteria and fungi do not spontaneously appear in sterile, nutrient-rich media.

11. HOW did life Begin? Hydrothermal Vents Electric Spark
These vents release important hydrogen-rich molecules
Mineral catalysts could have made critical reactions occurs faster
Can generate amino acids and sugars from an atmosphere loaded with water, methane, ammonia and hydrogen
Demonstrated in the famous Miller-Urey experiment reported in 1953
New evidence suggest that it may have occurred in volcanic clouds

12. How did the first organic compounds form?
Experiment conducted in 1953 by
Staley L. Miller and Harold C. Urey
Their apparatus, illustrated in the figure included a:
Gas chamber containing gases present in Earth early atmosphere
Electrodes supply electricity to provide energy to drive chemical reactions
Water chamber substituted for the oceans and lakes.
The Miller-Urey experiment produced a variety of organic compounds, including amino acids.
Miller Urey – , , ,
Three Domains –

13. HOW did life Begin? Panspermia Community Clay Ice Earth
Life could have come from outer space in a comet or meteorite.
Clay may have provided the foundation for first organic compounds.
Mineral crystals in clay could have arranged organic compounds into organized patterns.
Ice Earth
3 billion years ago ice might have covered the oceans.
Protected from UV light, organic compounds may have formed and reacted with one another.

14. How did cells form?
Sidney Fox and other scientists have done extensive research on the physical structures that may have given rise to the first cells.
Cell like structures, including microspheres and coacervates, form spontaneously in certain kinds of solutions.
Coacervates and microspheres like cells can take up certain substances from their surroundings.
Coacervates can grow
Microspheres can bud to from smaller microspheres. However, microspheres and coacervates do not have all of the properties of life.
Unlike cells, microspheres and coacervates do not have hereditary material.

15. When did atmospheric Oxygen appeared?
About 2.7 b.y.a., cyanobacteria or blue-green algae began photosynthetic reactions
About 1.8 b.y.a, the atmosphere contained abundant free oxygen.
Allowed for the development of more complex, oxygen-breathing life forms
Caused the first mass extinction of organism that had evolved in an oxygen-less planet
Ended the process of chemical evolution
Spirulina

16. How did the first eukaryotes forms?
According to the endosymbiotic theory, eukaryotic cells formed from a symbiosis among several different prokaryotic organisms.
Eukaryote provided a beneficial environment
Prokaryote provided a method of energy synthesis.
Did not receive much support until the 1960s, when it was championed by Lynn Margulis of Boston University.
Aerobic prokaryote
Anaerobic eukaryote

17. What Evidence supports the Endosymbiotic Theory?
Mitochondria and chloroplasts contain DNA similar to bacterial DNA.
Mitochondria and chloroplasts have ribosomes whose size and structure closely resemble those of bacteria.
Mitochondria and chloroplasts, like bacteria, reproduce by binary fission.
Mitochondria and chloroplast replicate independently from the replication cycle of the cells that contains them.
Endosymbiosis –

18. What is the essential question?
Scientists explain that life arose from nonlife billions of years ago through the theory of abiogenesis. Could life arise from nonlife today? Explain.
Probably not. The same conditions no longer exist on Earth. The oxygen in the atmosphere would likely react with and destroy any new kinds of organic molecules or they would be consumed by bacteria and molds.