Aim: How do scientists explain the development of

life on earth?

What were the conditions on earth 4.5 billion years ago?

Harsh Early Earth

1)Hot2)Little Oxygen3)Abundant Lightning4) Volcanic Activity

Primitive Earth’s Energy Source

• As earth cooled, thunderstorms drenched the earth with water and the oceans formed. Lightning provided an energy source for life to begin.

• Inorganic compounds formed organic compounds.

Experiment by Stanley Miller & Harold Urey

Amino Acids, Nitrogenous Bases, Monsaccharides,

Fatty Acids

How did life begin on earth? Formation of Organic Compounds

Formation of Organic Polymers:Scientists have proven that polymers of organic compoundslike polysaccharides, polypeptides, lipids and nucleic acids could have formed during the conditions of early earth.

“RNA World”

Scientists hypothesize that the first genes were RNA. RNAserved as the both the molecule that stored the genetic info.& the molecule that directed protein synthesis.

Formation of Pre-Cells:

Experiments show that membranes can form aroundorganic polymers in a solution if certain kinds of lipidsare present.

**The simplest living organisms are far more complexthan these “pre-cells”

Where did life begin?

Today’s deep sea vents are populated with simple unicellularorganisms that may resemblesome of the earliest living cells.

First organism on Earth

Anaerobic prokaryote cells heterotrophs

The first organisms on earth were simple unicellular

organisms.

Where did the oxygen come from?

• Some of these early forms of life developed into unicellular Autotrophs (they got their energy from the sun and produced oxygen)

Aerobic Organisms

Now, that the new atmosphere had OXYGEN, organisms that could use oxygen

to do cell respiration slowly developed.

How do scientists explain this change from simple to more

complex organisms?

Theory of Evolution

1) The process by which species change over time (simple to complex).

2) Present day species arerelated to ancient species.

What is a theory?

Is an explanation, supported by observations and/orexperiments, that can be used to explain relatedoccurrences.

Theory ofEvolution

What is the evidence that supports the Theory of Evolution?

1) Fossil Record- collection of fossils that provides clues to the history of Earth’s organisms. The fossil record spansmuch of geologic time (billions of years of Earth’s history).

2) Similarities in Structure

3) Similarities in Development (Embryology)

4) Molecular Biology (DNA & Proteins)

How do we know that we have evolved from ancestors distinctly

different from us?

Hint: How do we know dinosaurs

existed?

The fossil record (remains of dead organisms) have given scientists the clues they needed to determine an organisms ancestry by comparing them to present day species.

FOSSILS

The fossil record shows…• Life has evolved from simple to more

complex

Older Organisms: more simplistic

Newer Organisms:more complex

What do we learn from fossils?

http://www.ucmp.berkeley.edu/education/explorations/tours/stories/middle/C7a.html

• How did behaviors evolve?

• How long did individuals live?

• How do features evolve over time?

http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html

Speciation

Evolution has lead to the formation of new species from different

ancient organisms

Species- a group of organisms thatshare certain characteristics & canmate with one another, producingfertile offspring.

• Descendents

CommonAncestor

Similar to a family tree

Descendents

Evolutionary Tree

Ancestral common species (bottom)

Species living at present time (top)

Our Common Ancestor

Unicellular CommonAncestor100’s of

Millions of year ago

How closely related are they?• Which organisms are

closely related? • Those who have a

recent common ancestor (a close point of intersection in a tree diagram)

• Which are distant relatives?

• Those who have a distant common ancestor (a far point of intersection in a tree diagram)

What organisms are our closest relatives? Why?

Summary of early evolution

Present day