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Origins of Life
• Early Idea: Spontaneous Generation– The idea that non-living material can produce
life—Life magically appears!
– Examples• Meat produces maggots• Mud produces fish (mudskippers)• Grain produces mice
Origins of Life
• Francesco Redi disproved the theory of spontaneous generation in 1668– Experiments with rotting meat
Origins of Life
• Also during this time, scientists were just beginning to use microscopes…
– They were able to see that microorganisms were EVERYWHERE!
– Even though Redi was able to disprove the theory of spontaneous generation, many scientists thought that microorganisms arose spontaneously from a “vital force” in the air
Origins of Life
• Louis Pasteur– Disproved the spontaneous generation of
microorganisms – Experiments with broth
Origins of Life
• Pasteur’s experiments showed that microorganisms do not arise from the broth alone even in the presence of air
• Biogenesis became the accepted theory about the origin of life– Biogenesis is the idea that living organisms
only come from other living organisms
How Did Life Begin On Earth?
• Currently, there is no way to know for certain how life began on Earth.
• Scientists have developed theories about the origins of life, using the scientific method to test hypotheses about conditions on early Earth.
• Only about 1% of all known species exist today– 99% are extinct!
How Did Life Begin On Earth?
• Early Earth– Very Hot – Meteorite Collisions – Volcanoes– Very little oxygen
• Atmosphere made of H2O Vapor, CO2, Nitrogen gas, Methane & Ammonia
• Ingredients for Life: Before life can occur, you need the molecules of life– 1st: Formation of simple organic molecules – 2nd: Organization into complex organic
molecules• Proteins/Carbohydrates/Nucleic Acids/Lipids
• So… How did this happen in such a harsh environment?
How Did Life Begin On Earth?
How Did Life Begin On Earth?
• Alexander Oparin (1930’s) – Life began in the oceans
• Sun, lightening & heat caused chemical reactions producing organic molecules
• These molecules washed into the ocean forming primordial soup
• Miller & Urey (1953) – Tested Oparin’s theory by
simulating conditions on early Earth in a lab
– Mixture of H2O vapor, ammonia, methane, and hydrogen gasses were zapped with electrodes
– Cooled gasses condensed in flask– After a week, several kinds of amino
acids, sugars, and other small organic molecules were present in the flask
How Did Life Begin On Earth?
• The next steps in the origin of life were the formation of complex organic molecules and cells.
– Sidney Fox – produced protocells by heating solutions of amino acids
• Protocells – a large ordered structure, enclosed by a membrane, that carries out some life activities, such as growth and division.
How Did Life Begin On Earth?
The First True Cells
• First forms of life were prokaryotes that likely evolved from protocells– Anaerobic Heterotrophs
– Later, early prokaryotes evolved to be able to make their own food
• These were similar to archaebacteria and used chemosynthesis to produce their food
The First Photosynthetic Prokaryotes
• Likely the next kind of organisms to have evolved were:– Able to use sun to make glucose– Produced OXYGEN, which
changed Earth’s atmosphere– Lightening + Oxygen = Ozone
Layer formation
The First Eukaryotes
• The Endosymbionic Theory– Lynn Margulis – 1960’s– Eukaryotes evolved
from prokaryotes– Evolved b/c of
symbiotic relationships between early prokaryotic bacteria (mitochondria & chloroplasts)
The Record Of Life
• Paleontologists – scientists who study ancient life, often using fossil evidence– Uses fossils to determine look and characteristics of
the organism, as well as the climate and geography of the area.
• Fossils – evidence of an organism that lived long ago – typically found in sedimentary rock
• compressed clay/sand/mud
The Record Of Life
• Different kinds of fossils:– Trace– Casts– Imprints– Petrified– Molds– Amber– Frozen
Mold Fossil
Cast Fossil
Imprint Fossil
Trace Fossil
Frozen FossilAmber Fossil
• Fossil Aging – Relative Dating – The deeper the fossil, the
older it is.– Radiometric Dating – Uses radioactive
isotopes to determine specific ages of fossils.• Potassium-40: used for really old fossils• Carbon-14: used for fossils less than 50,000 years
old
The Record Of Life
• Chronology, or calendar, of the Earth’s history.
– Based on evidence from rocks
– Organized according to living organisms of the time period
– 4 different eras
Geologic Time Scale
Time Line of Earth’s History 4.6 billion ybp – Earth forms
hot/volcanoes/meteors/ancient atmosphere
3.9 billion ybp – Earth cools water vapor condenses. Millions of yrs of rainstorms create oceans
• 3.9-3.5 billion ybp – Precambrian Era – First organisms appear, photosynthesizing organisms add OXYGEN
to atmosphere– 3.5 billion ybp – unicellular prokaryotes– 1.8 billion ybp – eukaryotic organisms develop– 544 million ybp – multicellular eukaryotes (sponges & jellyfish)
540 million ybp – Paleozoic Era Animals & plants appeared
500 million ybp – first vertebrates 430 million ybp – first land plants 390 million ybp – first amphibians 300 million ybp – first reptiles 250 million ybp – mass extinction
Time Line of Earth’s History
Time Line of Earth’s History
245 million ybp – Mesozoic Era Age of the Dinosaurs
• 245 million ybp – Triassic Period– 225 million ybp: first dinosaurs– 210 million ybp: first mammals
• 208 million ybp – Jurassic Period– 150 million ybp: first birds
• 144 million ybp – Cretaceous Period – 135 million ybp: continents broke apart & began to drift– 66 million ybp: mass extinction of dinosaurs
Time Line of Earth’s History
• 66 million ybp – Cenozoic Era – Era in which we now live
• 30 million ybp – Primates appear• 200,000 ybp – Modern Humans Appear