History of the Earth

Early Earth 4.6 bya• VERY HOT (colliding meteorites, erupting

volcanoes)• Atmosphere was mostly nitrogen, carbon

dioxide, water vapor, methane, ammonia but NO OXYGEN!!!

4.4 bya• Earth cools• water vapor condenses into rain creates oceans

(where the first life will form)

Scientific Evidence

• Can scientists be sure that Earth formed this way?

• No• the physical processes of Earth constantly

destroy and reform rock eliminating evidence.

Scientific Evidence

Evidence that we do have!• Fossils = evidence of an organism that lived

long ago and show the great diversity of life

Scientific evidence

• A person who studies fossils is called a paleontologist

Scientific evidence

How is a fossil made?• after an organism is

buried, the sand and clay around it harden to form sedimentary rock. Then erosion brings the fossil to the surface

Scientific evidence

Dating Fossils• Relative Dating- older rocks/fossils are on the

bottom, younger ones are on top• Absolute Dating (also called radiometric

dating)- measures the amount of radioactive substance left in the rock or organism and determines its actual age

Scientific evidence

• By examining rock layers and dating the fossils, scientists have been able to put together a chronology, or calendar of Earth’s history called the GEOLOGIC TIME SCALE.

Remember:Scientific Method

1. Observation2. Hypothesis3. Experiment & Collect Data4. Conclusion

Cell Theory1. all living things are made of cells2. cells are basic unit of structure & function3. All cells come from pre-existing cells.

What is the big question this theory raises?

Two questions:1. Where did the first cell come from?2. What can be observed now if it happened so long ago?

Origin of life• The initial belief was that life was created

through spontaneous generation (abiogenesis).

• Example: a piece of decaying meat produces maggots (baby flies)

Origin of lifeDisproving Spontaneous Generation• Francesco Redi was the first to disprove

spontaneous generation in the 1600s.

Origin of life

• Although Redi was able to disprove that large organisms did not simply appear, many scientists thought that microorganisms (bacteria) were so numerous and widespread that they must arise spontaneously- probably from a vital force in the air.

Origin of life

• Louis Pasteur in the mid 1800’s designed an experiment that disproved the spontaneous generation of microorganisms.

Origin of life

• From this time on BIOGENESIS, the idea life comes from life holds true.

• (Ex. Humans give birth to humans, mice to mice, etc.)

Origin of life

• But…. How did the very first life form that start this chain reaction?!!!

• The current theory is that life began in the oceans.

Origin of life

Oparin’s hypothesis: • Energy from the sun and lightning triggered

chemical reactions with the vapors that were present in the early atmosphere to produce small, organic molecules. Then, the rain washed the molecules into the ocean to create what is called the primordial soup (place of the origin of life).

Origin of life

PROOF??• 1953- Stanley Miller

and Harold Urey tested the hypothesis by simulating the conditions of early Earth in a lab.

Origin of life

Simple Molecules to Complex molecules?• Stanley and Urey’s experiments showed that

that simple molecules like amino acids when heated without oxygen link up to form proteins (complex molecules)

Origin of life

Complex Molecules to Cells?• - Sidney Fox showed how amino acid chains

will form protocells

Evolution of cells

1st cells = prokaryotic, anaerobic and heterotrophic what does heterotrophic mean?

2nd cells = autotrophic prokaryoteswhat does autotrophic mean?

3rd cells = photosynthesizing prokaryotes

Evolution of cells

First organisms were prokaryotes• 2 types– Archaebacteria – bacteria that live in harsh

environments, and more closely related to early prokaryotes

– Eubacteria- all other bacteria

Endosymbiotic theory

Endosymbiotic theory

• Pre-eukaryotic bacteria engulfed another – (mitochondria or chloroplast)

Eukaryotic organisms formed much later than prokaryotes