Earth’s HistoryA history including how life evolved, how the

geosphere changed and major extinction events.

Eons◦ErasPeriodsEpochs

Time periods

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

Pre-Achean Eon (Hadean Eon): Formation of Earth

Could organic molecules form in Early Earth?

Miller and Urey experiment

The first organic molecules

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 puzzle of life’s origin

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?

Archean Eon: First organisms

Endosymbiotic theory

Proterozoic Eon: Origin of Eukaryotic cells

Proterozoic Eon : What did Earth look like?

How did live begin to evolve into diverse life?◦ Asexual versus sexual reproduction◦ Multicellularity

Phanerozoic Eon: Diversity

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.

Paleozoic Era

Cambrian Period: What did Earth look like?

Ordovician Period: What did Earth Look like?

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.

Ordovician Period

Silurian Period: What did Earth look like?

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.

Devonian period

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.

Permian Period

Periods:◦ Triassic: “Age of reptiles”, fishes, insects, cone

breaing plants, mammals/◦ Jurassic: dinosaurs, birds.◦ Cretaceous: dinosaurs, birds, leafy trees, shrubs,

small flowering plants.

Mesozoic Era

Triassic Period: What did Earth look like?

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

Triassic period

Jurassic Period: What did Earth look like?

Cretaceous Period: What did Earth look like?

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).

Cretaceous Period

Periods:◦ Tertiary: marine mammals, grasses, large

mammals◦ Quarternary: humans

Cenozoic Era

Quaternary Period: What Earth looks like today.

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.

Quaternary Period