Transcript Day 1 Life on Earthx

A history including how life evolved, how the
geosphere changed and major extinction events.
 Eons
◦Eras
Periods
Epochs


Earth is approximately 4.6 billion years old.
Remember:
◦ How did Earth form?
◦ How are elements arranged?

Earth began to cool
◦ 4 billions years ago: rocks
◦ 3.8 billions years ago: water


Could organic molecules form in Early Earth?
Miller and Urey experiment


Geologic evidence suggests that about 200 to
300 million years after earth cooled enough
to carry liquid water, cells similar to modern
bacteria were common.
How did these cells originate?
◦ Microspheres
◦ Evolution of RNA and DNA

The first organisms were single celled
prokaryotic anaerobic cells that resemble
modern bacteria.
◦ Evidence: microscopic fossils in rocks
that are more than 3.5 billion years old.

Photosynthetic cells!
◦ How did the oceans go from brown to blue-green?
What color is the sky now?

Endosymbiotic
theory

How did live begin to evolve into diverse life?
◦ Asexual versus sexual reproduction
◦ Multicellularity

Periods:
◦ Cambrian: “Cambrian explosion”, hard parts, shells,
outer skeletons, invertebrates, arthropods.
◦ Ordovician and Silurian: aquatic arthopods, fishes,
first land plants, octopi and squid.
◦ Devonian: land plants, insecnts, vertebrates, sharks,
“age of fishes”.
◦ Carboniferous (Mississipian/Pennsylvanian) and
Permian: amphibians, reptiles, winged insects,
ferns.




Most organisms lived in the sea at this time.
The sea level dropped caused by plate
tectonics.
The majority of land mass was over the south
pole at this time and was a large glacier.
Approximately 57% of Earth’s species went
extinct at this time.


The third extinction event occurred at the end
of this period.
It was caused by
◦ fluctuating sea levels because more glaciers pulled
water from the oceans.
◦ and global cooling due to land plants removing
CO2 from the atmosphere.

There was approximately a 50% extinction of
the species on Earth.


This is the fourth extinction event.
It is often called the “Great Dying” event and
was caused by:
◦ Eruption of Siberian Volcanoes
◦ Formation of Pangaea disrupted ocean currents
◦ Possible meteor impact

This resulted in an 83% extinction event
◦ About 96% of all marine species
◦ About 70% of all land vertebrates
◦ Many arthropods and land plants also died.

Periods:
◦ Triassic: “Age of reptiles”, fishes, insects, cone
breaing plants, mammals/
◦ Jurassic: dinosaurs, birds.
◦ Cretaceous: dinosaurs, birds, leafy trees, shrubs,
small flowering plants.


This is the fifth extinction event
Caused by the eruption of the central Atlantic
province.
◦ Sulfur gas blocked the sun
◦ Large amount of lava released over several
centuries.

This was a 48% extinction and a majority of
the species that went extinct were marine
◦ Ammonites
◦ Corals
◦ Seed ferns


At the end of the cretaceous period there was
a sixth mass extinction event.
It is often referred to as the “K-T Boundary”
and was likely caused by
◦ Pangaea breaking up,
◦ Eruption of Deccan Volcanoes in India
◦ And possibly an asteroid impact.

It marks the end of the cretaceous
period/Mesozoic era, the “age of reptiles”
(dinosaurs).

Periods:
◦ Tertiary: marine mammals, grasses, large mammals
◦ Quarternary: humans



73,000 years ago there was an event that led
humans to near extinction.
It was caused by the Toba super volcano on
the island of Sumatra. It disrupted
ecosystems on a global scale.
Only a few ‘pockets’ of individuals remained,
estimated at around 10,000 total.