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