EARTH’S EARLY HISTORY:The formation of the planet and the beginning of life

AN IMPORTANT NOTE:

These large-scale hypotheses are based on a relatively small amount of hard evidence. Because of this, these exciting inferences will without doubt develop, improve, and even change over time.

HOW THE PLANET FORMED

FORMATION OF PLANET EARTH

4.6 billion years ago

Cosmic debris

Collisions, compression, decay…HEAT

FORMATION OF PLANET EARTH

Differentiation:

Iron sank

Less dense “floated” to form crust

Least dense = first atmosphere

EARTH’S EARLY ATMOSPHERE

Very different from today’s atmosphere: Much hotter Frequent volcanic eruptions Little or no oxygen Toxic to us!

vs

SETTING THE STAGE FOR LIFE

3.8 billion years ago, Earth cooled, water in liquid form

Global ocean

Here, life will somehow form!

ANIMATION

http://www.precisiongraphics.com/portfolio/animation/

THE FIRST ORGANIC MOLECULESLife cannot begin without these!

HOW DO WE GET LIFE?

Living things can come from non living things

All living things must come from a living thing

Spontaneous Generation

Biogenesis

In the mid 1600’s Francesco Redi decided to find out…

REDI’S EXPERIMENT: DO FLIES SPONTANEOUSLY GENERATE ON ROTTING MEAT?

Uncovered jars with rotting meat

Covered jars with rotting meat

Air could pass through but not flies

Control Group Experimental Group

RESULTS: BIOGENESIS

TWO MORE EXPERIMENTS…1700’S

Lazzaro Spallanzani: Tried to prove micro-

organisms did not come from a “vital force” in the air

Opponents said that he heated the flasks for too long removing the “vital force”

FINALLY AN ANSWER…MID 1800’S

Louis Pasteur Similar to Spallanzi’s

but allows for the air to continue to be exchanged with the outside

Curve prevents solids from passing into the flask

FINALLY Accept Biogenesis

THE FIRST ORGANIC MOLECULES

Could organic molecules have evolved under the conditions of early Earth?

2 American chemists tried to answer that: Miller and Urey

MILLER AND UREY EXPERIMENT

Showed that mixtures of organic compounds necessary for life can be created from simpler compounds that were present on early Earth

IMPORTANT NOTE:

Not accurate!

Corrected, showed that organic compounds CAN form under these conditions…even cytosine and uracil, two bases found in RNA!

LIFE’S ORIGINS

PROTEINOID MICROSPHERES

Organic molecules forming bubbles

Selectively permeable membranes

Can store and release energy

Similar to modern cell

RNA AND DNA

RNA molecules can form

Theory: could these early forms of RNA (that predate more complex DNA and RNA molecules) have found a home inside a microsphere?

OXYGEN

The fossil record photosynthetic bacteria

Rising levels of oxygen in atmosphere

The rise of oxygen drove some life forms to extinction (it was toxic to them), while other life forms were able to thrive

THE BEGINNING OF MODERN LIFEEukaryotic Cell Origins

ORIGIN OF EUKARYOTIC CELLS

Prokaryotic cells

Internal membrane nucleus

Cells with a nucleus! The first eukaryotes!!!

ORIGIN OF EUKARYOTIC CELLS

Endosymbiotic Theory

EVOLUTION OF MULTICELLULAR LIFEThrough 4 eras

PRECAMBRIAN ERA

650-544 million years ago

Simple anaerobic life forms Photosynthetic life develops adding oxygen

to the atmosphere Eukaryotes appear

Life still only in the sea!

PALEOZOIC ERA 544-245 million years ago

Diversity of marine life First vertebrates First organisms walked on land Plants and insects appeared Mass extinction – 95% of life dies out!

MESOZOIC ERA 245-65 million years ago

Appearance of dinosaurs (which later dominate the land on Earth) Small mammals develop Leafy trees, shrubs, and flowering plants

develop Mass Extinction – 50% of life dies out

CENOZOIC ERA 65 million years ago – present

Plants and insects thrive Mammals adapt to environment well and

dominate life on Earth Appearance of human ancestors Ice age

BUT HOW DO WE KNOW THIS?Fossilization and Determining Ages

FOSSILIZATION

Fossil = remains or traces of an organism that died long ago

Ways to make a fossil Sedimentary Rock Amber Volcanic Ash

SEDIMENTARY ROCK – RELATIVE DATING

Principle of Superposition (1669) – if rock strata (layers) have not been disturbed, the lowest stratum was formed first

Relative Age – age compared to other fossils, determined by location in the strata

RADIOMETRIC DATING

Compare the amount of a naturally occurring isotope to its decay products.

Absolute Age – age of the rock as determined by radiometric dating

Half Life – Time it takes for half of the material to decay