Earth Science 13.2A Paleozoic Era : Life explodes

Paleozoic Era : Life Explodes

Paleozoic Era

The Paleozoic Era followed the Precambrian period, running from 542 million years ago to 251 million years ago.

Throughout the Paleozoic era, there were major developments in the evolution of life. Many of these developments occurred in response to environmental changes.

Each species is fitted to survive in a particular type of environment. If the environment changes too much; the species must evolve or die off.

Trilobite fossil from earlyPaleozoic era

Paleozoic Era Environmental changes that have

affected the course of evolution on Earth include The formation and breakup of

continents Mountain building Volcanic activity Changes in climate Changes in sea level

Such changes have affected evolution throughout geological time.

Rapid change can lead to mass extinction; the extinction of many groups in a short amount of time. Fossil records show that with each mass extinction; life rebounded back as new species evolved.

Trilobite fossil from earlyPaleozoic era

Paleozoic Era

The Paleozoic Era divides up into 6 time intervals called periods Cambrian period (542 – 488

million) Ordovician period (488- 444) Silurian period (444 – 416) Devonian ( 416 – 359) Carboniferous period (359 –

299) Permian (299 – 251)

Many firsts in the history of evolution occurred during this era; from the first organisms with shells up to the first birds and flowering plants.

Trilobite fossil from earlyPaleozoic era

Paleozoic Era: Cambrian period

Cambrian Period: (542 – 488) As during the Precambrian era,

life in the early Paleozoic was found only in the seas.

But the Cambrian period (542- 488) brought dramatic changes to Earth.

Many new groups of organisms evolved in a relatively short time in an event geologists refer to as the “Cambrian explosion”.

Paleozoic Era: Cambrian period

Cambrian Earth:

Geologic developments contributed to the Cambrian explosion. The breakup of the supercontinent Rodinia formed many pieces of continents.

New environments formed in the shallow seas between these pieces, some of which lay near the equator.

Earth continued to warm after an ice age that had chilled the planet in the late Precambrian. This warming trend may have been a factor in the evolution of new living organisms.

Paleozoic Era: Cambrian period

Cambrian Life: As a result of the Cambrian

explosion, the number of different kinds of organisms increased greatly in only 15 million years.

Cambrian organisms are well know from the Burgess shale, a fossil-rich formation in the Canadian Rockies. Most Burgess shale fossils belong to several groups of invertebrates.

An invertebrate is an organism that lacks a backbone. The Burgess shale fossils also include early ancestors of vertebrates, organisms that did have backbones.

Paleozoic Era: Cambrian period

Cambrian Life: Cambrian animals were the first

to evolve hard parts such as shells.

The shells of mollusks, such as clams and snails, protected them from dangers in their environments.

Shells also allowed body organs to function in a more controlled environment.

Animals called arthropods evolved that had an external skeleton made of a protein called chitin.

Modern day arthropods include insects and crustaceans.

Paleozoic Era: Cambrian period

Cambrian Life:

One arthropod that developed early in Cambrian life was the trilobite.

A trilobite’s exoskeleton allowed it to burrow through soft mud in search of food.

More than 600 types of these mud burrowing scavengers evolved worldwide during this era.

Geologists also found limestones from the Cambrian period that began as reefs in the oceans. Cambrian reefs were made up of the remains of sponges or mats of material produced by cyanobacteria.

Paleozoic Era: Ordovician period

Ordovician period: (488-444) Major developments

During the Ordovician period, more complex communities of organisms developed in the oceans.

The first land dwelling plants evolved.

This period ended with a mass extinction.

Paleozoic Era: Ordovician period

Ordovician Earth:

Plate movements pushed the huge landmass of Gonwanda south during the Ordivician.

Part of five of today’s continents are made up of Gonwanda: South America, Africa, Australia, Antarctica, and parts of Asia.

Collisions between landmasses near the equator led to mountain building in what is now eastern North America.

Paleozoic Era: Ordovician period

Ordovician Ocean Life:

During the Ordovicain period, the diversity of organisms living in the ocean increased. For example, reef-building invertebrates called bryozoans evolved, along with early corals.

Trilobites continued to be abundant, and shelled organisms called brachiopods became even more common.

Vertebrates became more common as jawless fishes evolved. Jawless fishes had a bony, external covering and are the ancestors of today’s modern fishes.

Brachiopod fossils

Ordivician jawless fish

Paleozoic Era: Ordovician period

Ordovician Plant Life:

Another major development in the Ordovician period was the development of land plants.

These first plants resembled small, primitive plants such as liverworts.

They lived in moist areas and reproduced through spores, not seeds.

As plants multiplied on land, they added oxygen to the atmosphere.

Geologists think that an ice age caused a mass extinction at the end of the Ordovician period. Volcanic eruptions may have contributed to this event.

Modern day liverworts

Paleozoic Era: Silurian period

Silurian Earth: (444-416) The Seas

During this time, several factors caused sea levels to rise, flooding low lying parts of continents.

Large barrier reefs formed in these shallow seas.

The reefs restricted circulation between shallow marine basins and the open ocean.

Water in these basins evaporated, depositing large quantities of rock salt and gypsum.

Silurian Period

Paleozoic Era: Silurian period

Silurian Earth: Life

In the oceans, reef building corals developed. Jawless fish survived, developing thick armored plates.

The first jawed fish evolved during this period.

Other ocean organisms during this period include arthropods called eurypterids.

On land, small plants similar to mosses spread over moist lowland areas. The first vascular plants evolved.

eurypterid

vascular plant

Paleozoic Era: Silurian period

Silurian Earth: Plant Life

The stem of a vascular plant contains thin tubes that carry liquids within the plant.

These early plants were leafless spikes about the size of your index finger.

There is no evidence from trace fossils that arthropods began to adapt to life on land during the Silurian period.

The Rhyniophyta comprise the oldest known division of vascular plants during the Silurian period of 400 million years ago. The shoot is leafless and dichotomously branched in the genus Rhynia. Cooksonia is the oldest known vascular plant.