9.2- The Evolution of Multicellular Life

Earth’s HistoryMany events have happened throughout Earth’s history, causing the extinction of different plants and animals that were not able to adapt to survive.

● Ice age● Continents moved● Carbon dioxide levels changed

An ice age, also called “snowball earth”

Snowball Earth2.10 Snowball Earth; It Did Freeze Over!

Organisms’ HistoryBecause of the changes on Earth, organisms with special evolved adaptations were able to survive their new environments.

● Sexual reproduction- allowed some organisms to survive● By working in colonies, individual cells were able to work together.

○ These small individual cells eventually became one larger organism

Geologic Time ScaleDivides Earth’s history into sections based on major events and changes.

Just like we divide one year into months, weeks, and days, we can divide the Earth’s history into Eons, Eras, Periods, and Epochs

We will focus on a few eras and periods and some of the important things that happened within them

The Precambrian ExtinctionThere have been 5 mass extinctions throughout Earth’s history (some believe we are currently going through a 6th mass extinction).

In the precambrian extinction, most species that existed quickly disappeared from Earth.

● This is probably due to climate change and land change

The Cambrian PeriodAfter the precambrian extinction, there was space for new organisms to form. This lead to the Cambrian explosion.

New animals, such as sponges, formed during this time

4.2- Cambrian Explosion

The Permian PeriodDuring the Permian Period, continents moved together to form Pangea.

● Pangea is known as a supercontinent because all of the continents that we know today moved together to create one large land mass.

The Mesozoic EraThis era is known as the “Age of Dinosaurs.”

It is split into three periods:

1. Triassic- dinosaurs first started to evolve from reptiles2. Jurassic- “golden age of dinosaurs,” dinosaurs roamed the earth; the

first birds developed3. Cretaceous Periods- Largest dinosaurs (T. rex)

An asteroid hit the Earth, causing dinosaurs and many other organisms to die out.

How Dinosaurs Went Extinct!

Mount St. Helens (Volcano, 1980)

Mount St. Helens Erupts

Mount St. Helens (Volcano, 1980)

Yellowstone Caldera

Yellowstone Caldera

The Cenozoic EraKnown as the “Age of Mammals.”

Mammals evolved and became the dominant animals on Earth.

● Primates● Woolly mammoths● Early horses and deer

This is the Era we are in today!

The Quaternary PeriodWe are currently in the Quaternary Period:

● At the beginning of the Quaternary Period, Earth cooled, and there were more ice ages.

● Land bridges were created during the ice ages (because the water was frozen), so animals were able to migrate to different continents.

KQED Ice Age Bay Area

Human Evolution7.9- The Rise of Humans- Getting a Leg Up on the Competition