The Vendian Period began about 650 million years ago and ended about 543 million years ago. This period was when plants were the first living thing on earth. It also began the Cambrian Period.

Scientist call the Cambrian Period the "Cambrian Explosion" because many organisms had hard parts including shells and outer skeletons. In this period the first known represented of most animal phyla evolved. Invertebrates, such as jelly fish, worms, and sponges crawled along the sandy bottom. Arthropods also crawled along the sandy bottom, witch are Invertebrates with segmented bodies jointed limbs and an external skeleton.

In this period of time ancestors of the modern octopi and squid appeared also aquatic arthropods. Some even became the first animals to live on land. Among the first vertebrates (animals with back bones) to Appear were jaw less fishes, witch had sucker like mouths. Also the first land plants evolved.

The Silurian Period was also part of the Ordovician Period. In this period also aquatic arthropods appeared. Even land animals appeared. Many octopuses and squids also evolved from aquatic ancestors. Plants started to grow low on the ground in dump areas.

Insects started appearing on land during this period. In the seas both invertebrates and vertebrates thrived. They also called the Devonian Period the ages of fishes because many group of fishes were present in the ocean. Most fishes of this time had jaws, bony skeletons, and scales on their bodies. During this time vertebrates began to invade the land.

In this period most plants started to form into vast swampy forest. At the end of the Paleozoic Era many organisms died out. This was called mass extinction. It affected both plants and animals on land and seas. About 95% of the complex life in the oceans disappeared.

The Permian Period extended through the continents. Other groups of vertebrates, such as reptiles evolved from certain amphibians. Reptiles are animals that have scaly skin and lay eggs with tough leathery skin like the ones we have until this day. Winged insects evolved into many forms including huge dragonflies and cockroaches.

Organisms that survived the Permian mass extinction became the main forms of life early in Triassic. Important organisms in this ecosystem were fishes, insects, reptiles, and conspiring plants. Reptiles were successful in this era. This era is often called "Age of Reptiles". About 225 million years ago the first dinosaur appeared. One of the first dinosaurs was a meat eater that had light and ran swiftly on it's hind legs.

In this era dinosaurs became the dominant animals on land. Dinosaurs ruled Earth for about, 150 million years, but different types lived at different times. One of the first birds was called Archaeopteryx, appeared during this time. Many paleontologist now think that birds are relatives of dinosaurs.

Reptiles were dominant vertebrates during this time. Dinosaurs such as meat-eating Tyrannosaurus Rex dominated land ecosystems, while flying reptiles and birds soared in the sky. However flying reptiles became extinct during this time. This era also brought new forms of life, including leafy trees, shrubs, and small flowering plants like today.

Earths climates were generally warm and mild. Marine mammals such as whales and dolphins evolved. On land flowering plants and insects flourished. Grasses evolved providing food source. Some mammals became very large, as did some birds.

Mammals that evolved during Tertiary Era eventually faced a changing environment during this era. Earth's climate cooled, causing a series of ice ages. Continental glaciers advanced and retreated over parts of Europe and North America. Earth's water froze in continental glaciers that the level of the ocean fell by more than 100 meters. Then about 20,000 years ago, Earth's climate began to warm.