The History of Life on Earth and its driving force:

How did life begin on earth?

Your Hypotheses? Journal Entry (three minute power write

and then finish at home.)

Some actual scientific theories on the beginning of

life on earth.

Early scientific theory: Spontaneous Generation

Definition: Life from non-life Examples:

Mud +Water = Ducks and Swans Dirty Shirt + Hay = Mice Maggots from Dead Animals

In 1658 Francisco Redi’s experiment on flies

disproves spontaneous generation.

1862 Louis Pastuer’s broth and bacteria experiment

also disproves spontaneous generation.

Today scientists believe life came from life:

BIOGENESIS

If biogenesis is true, how did it begin?

Not spontaneous generation, but spontaneous origin.

Early earth was a harsh environment.

CO2,N,SO2,H2S,NH3,CH4

Spontaneous Origin: Chemical reactions of non-

living matter forming simple organic molecules.

These molecules energized by the sun and volcanic heat formed more complex molecules

These molecules became the building blocks of cells.

Miller and Urey’s experiment (1953)

Mixed water vapor, methane, ammonia and hydrogen gases in a reaction chamber, after one week’s time they found amino acids and other organic compounds.

Today scientists believe their model was slightly flawed.

Primordial Soup: Earth’s early oceans

Louis Lerman’s Bubble Model.

(1986) Gases from undersea volcanoes

protected and concentrated. Ejected into the atmosphere and

exposed to lightning and uv radiation.

Fall back into the ocean as simple and complex organic compounds.

Some scientists think the molecules for life may have originated from Space.

Panspermia — the theory that microbes transmit life to habitable bodies in space; or the process of such transmission.

Starting in the 1970s, British astronomers Fred Hoyle and Chandra Wickramasinghe rekindled interest in panspermia. They found new evidence, traces of life, in the intervening dust. They also proposed that comets, which are largely made of water-ice, carry bacterial life across galaxies and protect it from radiation damage along the way. One aspect of this research program, that interstellar dust and comets contain organic compounds, has been pursued by others as well. It is now universally accepted that space contains the "ingredients" of life.

There is a big jump from organic molecules to life

on earth.

Microspheres: tiny vesicles of organic molecules may have been the first step to cellular organization.

Lipid structure: Hydrophobic. There is a lot left to be learned

Early mulitcellular life

Scientists have found the first multicellular animals that apparently live entirely without oxygen, Loricifera. The creatures reside deep in one of the harshest environments on earth: the Mediterranean Ocean's L'Atalante basin, which contains salt brine so dense that it doesn't mix with the oxygen-containing waters above. The creature's cells apparently lack mitochondria, the organelles that use oxygen to power a cell. Instead they are rich in what seem to be hydrogenosomes, organelles that can do a similar job in anaerobic (or oxygen free) environments. The find could help scientists understand what life might have looked like in the earth's early oceans, which also had very little oxygen.

Loricifera.

Earliest Fossils found were 3.5 billion years old.

2.5 billion years ago photosynthesis evolves What impact did this cause?

Complex cells develop from Endocytosis/symbiosis (endosymbiosis)

Early life was prokaryotic, heterotrophic, and anaerobic.

1.5 billion years ago eukaryotic organisms evolve.

Fossil Record: Our Key to Life’s History

Fossils are usually found in sedimentary rock when hard parts of organisms are quickly buried in sediment.

Fossils are any evidence of past life Examples include shells, casts,

molds, bones, prints, frozen soft tissues, teeth, and others.

Paleontologists study fossil record.

They learn where to look for fossils by looking at what is going on today.

By using geologic events that take place today scientists can figure out the past.

Piece together the clues to life and the environments in which they lived.

Uniformitarianism:

“The present is the key to the past.” Geologic forces that are taking place

today took place in the past. Where do you think fossils would be

best found? Consider areas where sediments would

collect and fast burial would take place. Examples?

Father of modern GeologySir Charles Lyell

(1797-1875)

Explain his law of uniformitarianism to your table partner and provide an

example?

Dates and ages of fossils, How do paleontologists

know?

Absolute vs. Relative time measurements.

Absolute time: the actual age of a fossil or life form.

Relative time: the comparison of a fossil or object to something else such as another rock or fossil.

Tree rings can identify absolute dates based on their annual growth of tissues.

Absolute time uses radiometric dating.

Radioactive T1/2 (half life) the time it takes for 1/2 of the unstable radioactive isotopes to become stable.

Based on the known rate and the known percentages of atoms in a fossil or rack the absolute age can be determined.

Carbon Dating:T 1/2 problem.

A bone is found with 12.5% carbon 14 atoms and 87.5% nitrogen 14 (a stable atom) the T 1/2 for carbon 14 is 5,600 years. If the ratio of carbon 14 to Nitrogen 14 was 100% to 0% at the time the animal was alive how old is the fossil now?

Hint: :How much C14 will be left after 5,600 years?

Using relative and absolute dating methods, paleontologists have created a geologic time

scale from the layers of sedimentary rock.

Relative Dating of rock layers and fossils/environments: Which rocks and

fossils are the oldest? Why?

Geologic Time Scale

As you examine the geologic time scale note the key events, simple to complex progression of

life, mass extinctions, and humans position relative

to other life forms.

A change in a population of organisms over time is

known as:

•Evolution•What is the definition of population?

Population:A group of organisms of

the same species within a given area.

Six different points of evidence for

evolution

#1 Fossil record

• The fossil record develops from simple to complex.

• Demonstrates gradual changes over time.

• Combinations of fossils in the rocks allow us to reconstruct the ancient communities and thus probable ecosystems.

Fossil environments

The gap of life in the fossil record lead people to argue for

the theory of creationism.

Very little life before the Cambrian time period. (600,000,000 years ago)

Then there is an explosion of life in the fossil record.

Why?

Scientists have a different explanation for why the sudden explosion in the fossil record.

What do you think might cause the sudden appearance of many types of fossils. Hint:What are the requirements for a fossil to form? Discuss with your lab partner.

#2 Homologous Structures:

• Characteristics on modern organisms that are similar because they most likely were inherited by a common ancestor

• Examples:->

#3 Vestigial Structures

• Body parts no longer used but still present from an earlier ancestor.

Picture

#4 Analogous Structures

• Structures that are similar in purpose but not inherited from a

common ancestor.• Environmental pressures are solved in a similar but slightly

different manner.

Picture

#5 Ontogeny Recapitulates

Phylogeny (embryonic

development)

• During fetal development higher vertebrate organisms resemble

less developed vertebrate organisms with tails, gill slits, etc.

3 week old human embryo

Yes, you looked like this! Yikes! Human embryo 4.5 weeks

Note tail and gill slits in human embryo at 5 + weeks

#6 Comparative Biochemistry

• Examples:• Cell organelles and cell structure

similarities.• Protein synthesis DNA/RNA code.• C&G, A&T for all life forms, we can

inject human DNA into bacteria and the bacteria will build human protein.

• Photosynthesis and Respiration complement each other.

Mechanisms for Evolution

• What makes it happen?• Your ideas?

Early Theories

• Lamark believed in the theory of acquired characteristics.

• Organisms constantly strive to improve themselves.

• The effort to improve causes the most used body structures to develop.

• Once a structure has been modified it is inherited by the organisms offspring.

Example of Lamark’s idea of acquired characteristics in Giraffes

1889 August Weisman cut the tails off of hundreds of mice for 22 generations to disprove Lamark. OUCH!

1844 Darwin and Wallace formulated the theory of natural selection as the driving force for

evolution.

Tenets of Natural Selection

• Variation exists within the population• Some individuals in a population are

better suited to the environment• More offspring are born than can

survive.• Over time traits that are favorable

spread throughout the population

Where do you think most of the variation for a

population originates?

While it is true that mutations account for

variation most variations come from existing

combinations of alleles. (remember them?)

Sources for recombination of existing alleles are. . .

• Independent assortment• Crossing over during meiosis• Combination of sperm and egg

The impetus for evolution comes from the

environment as it changes over time.

• What might cause the environment to change?

• Examples of how it might change:

Present day examples of natural selection:

• English pepper moth• Predator/prey relationships• Exotic species introductions• Geographic isolation/Island

Biogeography• Pesticides (DDT)• others

Genetic Equilibrium is when a population is not evolving and allele frequency is constant.• Random mating• No environmental pressure• No migration• No mutations

• Does this happen?

If an accidental change in gene frequency takes place it is known as:

•Genetic Drift• Example:

What defines a species?

• Your definition?• An interbreeding population that

can produce healthy, fertile offspring.

Evidence of species evolution can be seen in

the representatives of life on earth today.

• Isolation (divergent evolution)• Adaptive radiation• Convergent evolution

Isolation forms new species

The Environment drives the change.

Divergent evolution: Isolated populations evolve

independently

Adaptive Radiation:

Multiple branching of a family tree,

new environments may have many available niches.

Convergent Evolution: Different Types of Organisms Evolve Similar

Characteristics.

Convergent evolution in marine life

THE END

• OR IS IT STILL JUST THE BEGINNING?• GEOLOGIC TIME WILL TELL.