1. Earth's Timeline

2. Paleozoic Era Explosion of life
During the Cambrian Period there was so many new life forms appeared in a relatively short time.
At this time, all animals lived in the sea.
Many were animals without backbones or invertebrates. Example: sponges, worms, jellyfish, brachiopods (two shells) and trilobites.
During the Ordovician and Silurian periods the ancestors of modern octopus and squid appeared. During this time, jawless fish evolved. Jawless fish were the first vertebrates.

3. Paleozoic Era
Until the Silurian Period, only one- celled organisms lived on land.
During the Silurian plants grew low to the ground.
By Devonian Period plants grew in drier areas.
Both invertebrates and invertebrates lived in the Devonian Seas.
Devonian was known as the Age of Fish
During this period animals began to invade land.
Amphibians began to appear.

4. Paleozoic Era During this era life expanded over Earth’s continents.
Small reptiles began to appear.
During the Carboniferous Period, winged insects evolved into many forms.
During the Paleozoic Era a mass extinction occurred. Both plants and animals on land and in the sea became extinct. Scientist do know the what caused the mass extinction.
During the Permian Period, about 260 million years ago, Earth's continents moved together to form a great landmass, or super continent, called Pangaea.

5. The Mesozoic Era Some animals survived the mass extinction.
Plants and animals that survived included fish, insects, reptiles and cone bearing plant called conifers.
This was know as the Age of Reptiles
During the Triassic period mammals first appeared.
During the Jurassic period, dinosaurs became the dominant animals on land.
During Cretaceous Period dinosaurs and other reptiles still dominated. Flying birds and reptiles competed for places in the sky. Flowering plants evolved, flowering plants produce seeds that are inside a fruit. This fruit help the seeds survive.
At the close of Cretaceous Period ,about 65 million years ago, another mass extinction occurred. Scientist hypothesize that this mass extinction occurred when an object from space struck Earth. This object was probably an asteroid.
When the asteroid hit Earth it created a huge amounts of dust and water vapor into the atmosphere.

6. The Cenozoic Era
During the Mesozoic Era ,mammals had a hard time competing with dinosaur for food and places to live.
The extinction of dinosaurs created an opportunity for mammals to thrive and survive. Mammals evolved to live in many different environments (land, water and air).
Tertiary Period Earth’s climate was warm and mild.
Quaternary period-Earth’s climate cooled, causing a series of ice ages. Large mammals roamed the ice-free parts of North America and Eurasia.
The fossil records suggest that modern humans may evolved as early as 100,000 years ago
We are Presently living in the Quaternary Period of the Cenozoic Era.