The History of Life. The Record of Life You may have seen thrilling movies or read books that describe travel in time. The characters often encountering.

The History of LifeThe History of Life

The Record of LifeThe Record of Life

You may have seen thrilling movies You may have seen thrilling movies or read books that describe travel in or read books that describe travel in time. The characters often time. The characters often encountering strange organisms. encountering strange organisms.

Did the differences you saw Did the differences you saw surprise you?surprise you?

After all, everything changes over After all, everything changes over time.time.

It is difficult to imagine what Earth It is difficult to imagine what Earth might have been like that long ago!might have been like that long ago!

Early History of EarthEarly History of Earth

Early Earth was inhospitable!Early Earth was inhospitable!

It was probably It was probably very hot, volcanoesvery hot, volcanoes might have erupted might have erupted frequently spewing frequently spewing gases gases and lavaand lava

• These gases helped form Earth’s early atmosphere which These gases helped form Earth’s early atmosphere which contained contained little oxygenlittle oxygen but but abundant carbon dioxide and abundant carbon dioxide and

nitrogennitrogen About About 3.9 billion3.9 billion years ago, years ago, earth might have cooledearth might have cooled enough enough

for for water in the atmosphere to condensewater in the atmosphere to condense• This would have led to millions of years of rainstorms, This would have led to millions of years of rainstorms,

enough to fill Earth’s oceansenough to fill Earth’s oceans It is in the oIt is in the oceans ceans that scientist propose that the that scientist propose that the first first

organismsorganisms appeared appeared between 3.9 and 3.5 billion yearsbetween 3.9 and 3.5 billion years ago ago

History in RocksHistory in Rocks

Scientist cannot be sure that earth formed in this Scientist cannot be sure that earth formed in this way. There is no direct evidence of the earliest way. There is no direct evidence of the earliest years of Earth’s history.years of Earth’s history.

The physical processes of Earth constantly The physical processes of Earth constantly destroy and reform rock. destroy and reform rock. The oldest rocks that have been found on earth The oldest rocks that have been found on earth

formed only about 3.9 billion years agoformed only about 3.9 billion years ago Rocks are an important source of information Rocks are an important source of information

about the diversity of life that once existed on about the diversity of life that once existed on the planetthe planet

Fossils – Clues to the PastFossils – Clues to the Past

The millions of species that live today are The millions of species that live today are probably only a small fraction of all the probably only a small fraction of all the species that ever existed.species that ever existed. About 99% of species are extinct – they no About 99% of species are extinct – they no

longer live on Earthlonger live on Earth Fossil – evidence of an organism that lived Fossil – evidence of an organism that lived

long agolong ago. . Scientists use fossils to learn about ancient Scientists use fossils to learn about ancient

species.species.

Fossils Cont.Fossils Cont.

A person who studies fossils is a A person who studies fossils is a PaleontologistPaleontologist

Fossils can form in many different ways.Fossils can form in many different ways. Fossils are used to understand Fossils are used to understand

Events that happened long agoEvents that happened long ago Kinds of organisms that lived in the pastKinds of organisms that lived in the past Behavior of organisms that lived in the pastBehavior of organisms that lived in the past Ancient climate and geographyAncient climate and geography

Could ferns have lived in Could ferns have lived in Antarctica?Antarctica?

Scientist have discovered fossil remains of Scientist have discovered fossil remains of ferns in the rocks of Antarctica. These ferns in the rocks of Antarctica. These fern fossils are related to ferns that grow in fern fossils are related to ferns that grow in temperate climates on Earth today.temperate climates on Earth today.

How did they get there?How did they get there?

Pangaea linkPangaea link

How fossils formHow fossils form

Fossils occur in sedimentary rocksFossils occur in sedimentary rocks What is a sedimentary rock?What is a sedimentary rock?

Fossils form when organisms are buried in Fossils form when organisms are buried in small particles of mud, sand or clay soon small particles of mud, sand or clay soon after they die.after they die. Over time, the particles compress and harden Over time, the particles compress and harden

into sedimentary rockinto sedimentary rock Fossils can still form today in the bottom of Fossils can still form today in the bottom of

lakes, streams and oceans.lakes, streams and oceans.

The Fossilization ProcessThe Fossilization Process

Describe how the movements of earth Describe how the movements of earth might expose a fossil.might expose a fossil.

Why do you think that fossils are rare in Why do you think that fossils are rare in igneous and metamorphic rock?igneous and metamorphic rock?

Follow this link to see the processFollow this link to see the process

Fossils in different layers of Fossils in different layers of sedimentary rock vary in agesedimentary rock vary in age

Ways of dating fossilsWays of dating fossils Relative datingRelative dating – The deeper the layer of rock, the – The deeper the layer of rock, the

older the fossil is. Layers closer to the top are older the fossil is. Layers closer to the top are younger (Geologic law)younger (Geologic law)

• Relative dating only gives you an Relative dating only gives you an estimate of ageestimate of age, not the , not the actual age of a fossilactual age of a fossil

Radiometric datingRadiometric dating – Uses radioactive isotopes in – Uses radioactive isotopes in rocks or fossils (radioactive isotopes break down over rocks or fossils (radioactive isotopes break down over time giving off radiation) time giving off radiation)

• Decay rate of the isotopes can measured – Decay rate of the isotopes can measured – half lifehalf life• Scientist use potassium-40 to date older samples (1.3 billion Scientist use potassium-40 to date older samples (1.3 billion

years) and years) and carbon-14carbon-14 to date fossils less than 50,000 years to date fossils less than 50,000 years oldold

The Geologic Time ScaleThe Geologic Time Scale

By examining layers of sedimentary rock and By examining layers of sedimentary rock and dating the fossils that are found in the layers, dating the fossils that are found in the layers, scientists have been able to put together a scientists have been able to put together a chronology (calendar) of the Earth’s history.chronology (calendar) of the Earth’s history.

Draw the geologic time scale on pg 383 and Draw the geologic time scale on pg 383 and 384. Be sure to include major life forms, major 384. Be sure to include major life forms, major events, the period, era and time in years on your events, the period, era and time in years on your time scale. Make your time line to scale.time scale. Make your time line to scale.

How do we know how old fossils How do we know how old fossils are?are?

Relative Dating – dating of fossils based Relative Dating – dating of fossils based on depthon depth Layers at the surface are younger than those Layers at the surface are younger than those

at deeper layersat deeper layers Just an estimate, not really accurateJust an estimate, not really accurate

Radiometric datingRadiometric dating – uses radioactive – uses radioactive isotopes in rocks or fossilsisotopes in rocks or fossils

Radioactive isotopes are atoms with unstable Radioactive isotopes are atoms with unstable nuclei that decay over time giving off radiationnuclei that decay over time giving off radiation

Radioactive isotopes form a new element after Radioactive isotopes form a new element after they decaythey decay

All radioactive isotopes have a characteristic All radioactive isotopes have a characteristic decay rate which scientist use decay rate which scientist use

Half life – time it takes for half of the Half life – time it takes for half of the radioactive isotope to decay into a new radioactive isotope to decay into a new element – used to measure decay rateelement – used to measure decay rate

ExampleExample When a rock forms it contains radioactive When a rock forms it contains radioactive

isotopes that decay to half of its original isotopes that decay to half of its original amount in 1 million years. Today, if a rock amount in 1 million years. Today, if a rock contained equal amounts of the radioactive contained equal amounts of the radioactive isotope and the new substance, the rocks isotope and the new substance, the rocks would be 1 million years old.would be 1 million years old.

Scientists use potassium-40, a radioactive Scientists use potassium-40, a radioactive isotope that decays to argon-40, to date isotope that decays to argon-40, to date rocks containing very old fossils.rocks containing very old fossils. Chemists have determined that potassium-40 Chemists have determined that potassium-40

decays to half its original amount in 1.3 billion decays to half its original amount in 1.3 billion yearsyears

Scientist use carbon-14 to date fossils less Scientist use carbon-14 to date fossils less than 50,000 years oldthan 50,000 years old

History of Life - ReviewHistory of Life - Review What was early earth like? What was early earth like? How do we think oceans were formed? When?How do we think oceans were formed? When? When and where do we think life began?When and where do we think life began? How do we know about organisms from the past?How do we know about organisms from the past? How do fossils develop?How do fossils develop? How can we determine the age of a fossil?How can we determine the age of a fossil? What four eras is the geologic time scale divided into? What types What four eras is the geologic time scale divided into? What types

of organisms mark each era?of organisms mark each era? The continents were at one time joined together in a landmass The continents were at one time joined together in a landmass

known as Pangaea. How long ago was that? Refer to your known as Pangaea. How long ago was that? Refer to your geologic time scale to understand when that occurred. geologic time scale to understand when that occurred.

Summarize the trend of how organisms developed during Earth’s Summarize the trend of how organisms developed during Earth’s history.history.

The Origin The Origin of Lifeof Life

Francesco Redi’s experiment Francesco Redi’s experiment (1668)(1668)

How do the results differ in the two How do the results differ in the two jars?jars?

What might you conclude from What might you conclude from these results?these results?

Louis Pasteur’s experiment – Louis Pasteur’s experiment – finally disproved finally disproved spontaneous spontaneous generationgeneration (mid 1800’s) (mid 1800’s)

Which came first, the chicken or Which came first, the chicken or the egg?the egg?

Biologists have accepted the concepts of Biologists have accepted the concepts of biogenesis for more than 100 yearsbiogenesis for more than 100 years

Biogenesis does not answer the question of how Biogenesis does not answer the question of how life began on Earthlife began on Earth

No one will ever know for certain how life began No one will ever know for certain how life began on earth. We can only make hypotheses about on earth. We can only make hypotheses about conditions on early Earth.conditions on early Earth.

How does chemistry become life??How does chemistry become life??

Evolution of complex moleculesEvolution of complex molecules

Primordial SoupPrimordial Soup Step 1: simple organic molecules must Step 1: simple organic molecules must

have formed (molecules that contain have formed (molecules that contain carbon)carbon)

Step 2: Simple organic molecules must Step 2: Simple organic molecules must have become organized into complex have become organized into complex organic molecules (proteins, carbohydrates, organic molecules (proteins, carbohydrates, and nucleic acids)and nucleic acids)

1930’s Oparin (Russian) – hypothesized 1930’s Oparin (Russian) – hypothesized that life began in the oceansthat life began in the oceans

Energy from sun and lightning triggered Energy from sun and lightning triggered chemical reactions to produce small chemical reactions to produce small organic molecules from substances in organic molecules from substances in the atmospherethe atmosphere

1953 Miller and Urey (American) – 1953 Miller and Urey (American) – replicated conditions in the lab and replicated conditions in the lab and produced amino acids, sugars, and other produced amino acids, sugars, and other moleculesmolecules

The next step…The next step…

How did we get from simple organic How did we get from simple organic compounds to complex organic compounds?compounds to complex organic compounds?

In the presence of heat, without oxygen, In the presence of heat, without oxygen, amino acids link to from proteins. ATP is amino acids link to from proteins. ATP is produced in a similar way.produced in a similar way.

Sidney Fox found that if you continued to heat Sidney Fox found that if you continued to heat the complex organic compounds the complex organic compounds protocellsprotocells developed.developed.

The Evolution of CellsThe Evolution of Cells

The first true cells…The first true cells… ProkaryotesProkaryotes that evolved from a protocell that evolved from a protocell Anaerobic (no oxygen present in atmosphere)Anaerobic (no oxygen present in atmosphere) Food – organic molecules abundant in oceansFood – organic molecules abundant in oceans Autotrophs evolved to inhabit harsh conditions Autotrophs evolved to inhabit harsh conditions

(ie. Archaebacteria)(ie. Archaebacteria)

Endosymbiont TheoryEndosymbiont Theory Eukaryotes probably evolved from prokaryote cellsEukaryotes probably evolved from prokaryote cells Theory proposes that eukaryotes evolved through a symbiotic Theory proposes that eukaryotes evolved through a symbiotic

relationship between prokaryotesrelationship between prokaryotes Evidence:Evidence:

• Chloroplast and cyanobacteria – resemble eachotherChloroplast and cyanobacteria – resemble eachother• mitochondria and bacteria – some look similarmitochondria and bacteria – some look similar• Chloroplast and mitochondria contain DNA that is similar to the DNA Chloroplast and mitochondria contain DNA that is similar to the DNA

in prokaryotesin prokaryotes• Today, some prokaryotes live in close association with eukaryotesToday, some prokaryotes live in close association with eukaryotes

Life TodayLife Today

Could new life originate on Earth today? Could new life originate on Earth today? List the specific evidence that supports each List the specific evidence that supports each

conclusion.conclusion. Life comes from existing lifeLife comes from existing life Life probably originated on Earth through the reaction Life probably originated on Earth through the reaction

of chemicals in Earth’s atmosphere and their further of chemicals in Earth’s atmosphere and their further reaction on Earth’s surfacereaction on Earth’s surface

Cells probably evolved as the chemicals on early Cells probably evolved as the chemicals on early Earth became more organized. Earth became more organized.