1. Earth Science 13.2B Paleozoic Era : Life explodes
Paleozoic Era : Life Explodes: Part B

2. Paleozoic Era: Devonian period
Devonian Earth: ( )
During the Devonian period, jawed fishes and sharks evolved in the seas.
Plants continued to colonize the land, along with insects and other small arthropods.
Later, amphibians evolved with adaptations for life on land.

3. Gondwana and Laurasia Devonian Earth:
A world map of Earth during the Devonian period would show two large continents.
Gondwana still occupied a large part of the southern hemisphere.
To the north, land masses collided to form a new large continent called Laurasia.
Laurasia included what is now North America, Europe, and parts of Asia.
As Europe and North America collided, mountains formed. Today, rocks from this past collision make up what is now parts of the Appalachian mountains.
Because Gondwana lay across the equator, western North America had a tropical climate.
The interior of Laurasia would have been hot and dry.

4. Devonian Life in the Ocean
Devonian Life: Ocean
Major developments in the Devonian seas include the appearance of many new types of jawed fishes and the evolution of sharks.
These jawed fishes had bony skeletons like those of present day fishes.
Sharks, in contrast, have skeletons made of softer material called cartilage.
Reefs formed by sponges and new types of corals continued to form in tropical seas.

5. Devonian Life: First forests
As land plants continued to evolve, the first forests developed. The Devonian forest was made up of large clubmosses, tree ferns, and twig like plants called horsetails.
There is fossil evidence that wingless insects, spiders, and centipedes lived in Devonian forests.
Toward the end of the Devonian, amphibians evolved from fishes. An amphibian is a four legged animal, with lungs for breathing, that can live on land but lays it’s eggs in the water. Frogs, toads, and salamanders are descended from early amphibians.
Devonian forest

6. Devonian Life: First forests
Devonian Life: First Amphibians
The fishes from which amphibians evolved probably lived in tidal flats or small ponds. They had primitive lungs as well as gills for breathing.
They probably used their fins to push themselves in soft mud.
Eventually these fishes evolved into true air-breathing amphibians with fishlike heads and tails, but with four legs.
Many types of amphibians rapidly evolved because they had little competition from other land animals.
Amphibians could eat the plants and insects that were already abundant on land.

7. Devonian Life: First forests
Devonian Life: First Amphibians
Two mass extinctions struck earth toward the end of the Devonian period.
The first affected mainly ocean organisms. For example, jawless and armored fishes became extinct.

8. Carboniferous period:
The Carboniferous period saw the development of great “coal swamp forests” in wet, tropical regions.
Amphibians and winged insects became common and the first reptiles evolved.
Geologists often divide the Carboniferous Period into two separate periods: the Mississippian and Pennsylvanian periods.

9. Carboniferous period:
During the Carboniferous period, there was a series of collisions between Earth’s major land masses.
Africa collided with the eastern edge of North America. This event formed what is now the southern Appalachian mountains.
By late in the period, landmasses began to merge to form the supercontinent of Pangaea.

10. Carboniferous period:
During the carboniferous period, flat, low-lying parts of continents flooded again and again as sea levels rose and fell.
In these areas, reef building organisms laid down huge deposits of calcium carbonate. Today, these deposits form thick layers of limestone.

11. Carboniferous period:
Among the animals that evolved during the Carboniferous period were the first reptiles.
Reptiles are animals that lay leathery shelled eggs that can survive out of water. Reptiles evolved out of amphibians. Reptiles could live in drier areas where amphibians could not survive.

12. Carboniferous period:
Vast swamps, called coal forest swamps, developed in wet tropical regions during the Carboniferous period.
The amphibians and winged insects that had recently evolved lived in these forests.
When the plants and animals in the swamp died, their remains built up in thick layers. Over millions of years, pressure and heat changed these layers of sediment into deposits of coal. The Carboniferous period takes it’s name from these coal deposits.

13. Permian period: Permian period: ( 299 – 251 )
As the Permian period began, earth’s continents were joined into the supercontinent Pangaea.
The evolution of life during the period continued trends that began during the Carboniferous period.
The Permian ended with the largest mass extinction in geological history.

14. Permian period: Permian period: ( 299 – 251 )
The formation of Pangaea greatly changed global environments during the Permian period.
Continental glaciers formed where Pangaea extended into the southern region. These ice ages in the southern hemisphere gradually ended when Pangaea drifted northward.
This led to a warming trend. Deserts formed in the center of Pangaea, which was far from any source of moisture. Today, huge deposits of red sandstone provide evidence of these deserts.

15. Permian period: Permian period: ( 299 – 251 )
As Earth’s climates warmed, sea levels fell. Many of the shallow continental seas dried up. As a result, there are few reefs dating to the Permian period.
Reefs still flourished in a few small ocean basins however. In what is now the southwestern United States, organic material from ocean organisms built up in the Permian Basin.
Over millions of years, these deposits formed the oil fields of Texas and New Mexico.

16. Permian period: Permian Life: ( 299 – 251 )
During the Permian period, life became more diverse on land and in the oceans. Conifers became abundant. New types of insects, amphibians, and reptiles evolved.
One group of the early reptiles were mammal-like reptiles.
Fossils show that their legs, skulls, and jawbones were similar to those of a later group – mammals.

17. Permian period: Permian Life: ( 299 – 251 )
Some mammal like reptiles had huge “sails” on their backs. These structures were formed from elongated spines covered with skin.
Dimetrodon (at right) had a sail which may have helped regulate body temperature.

18. Permian period: Permian Extinction: 251 million years ago
Nearly 250 million years ago, a mass extinction ended the Permian period. Scientists think that this extinction killed off 96% of all species.
Ocean organisms that became extinct included most brachiopods and bryozoans and all trilobites.
On land, most mammal-like reptiles died out, though a handful survived.

19. Permian period: Permian Extinction: 251 million years ago
Scientists aren’t sure what caused the Permian extinction.
One hypothesis is that huge volcanic eruptions in Siberia led to climate change.
Another hypothesis is that the climate change resulted from an asteroid impact in Antarctica.
Some scientists think that several factors at once contributed to the environmental climate changes that ended much of life on Earth.