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#           Paleozoic      

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Paleozoic (541-252 million years ago) means ‘ancient life.’ The oldest animals on Earth appeared just before the start of this era in the Ediacaran Period, but scientists had not yet discovered them when the geologic timescale was made. Life was primitive during the Paleozoic and included many invertebrates (animals without backbones) and the earliest fish and amphibians. 

Paleozoic signposts are colored green. The images show the art on the Trek Through Time signposts. The name of each period is a link to the entire plaque installed on the Trek Through Time.

### The Cambrian Period: 541 to 485 million years ago

**What did Earth look like during the Cambrian Period?**

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                            - One large supercontinent (Gondwana) and eight smaller continents, most of them located in the Southern Hemisphere.
                            - The area that is North America today stretched along the equator and a shallow sea covered part of the land.
                            - No continents near the poles, very little glacial ice.

**What was Earth’s climate like****during the Cambrian Period****?**
                            - The Earth had no polar ice caps.
                            - Warm and wet, without distinct seasons. 

**What animals were on Earth****during the Cambrian Period****?**
                            - Land animals hadn't evolved yet.
                            - Marine life flourished.
                            - Most major groups of invertebrates first appeared.
                            - Protective shells and exoskeletons evolved. Many unique and unusual invertebrates, which looked nothing like the animals of today, swam in the Cambrian seas.
                            - The most iconic invertebrates were trilobites, a group of arthropods similar to horseshoe crabs that ranged in size from a small coin to a tire.
                            - Crinoids, also known as sea lilies, lived attached to the seafloor, filtering plankton out of the water with their feather-like arms.
                            - The first vertebrates (animals with backbones) were primitive, jawless fish that first appeared near the end of the Cambrian Period.
                            - KIDS’ CORNER: Imagine that you’re swimming in a shallow, warm ocean and there are giant roly-polies swimming toward you! They can see you very well, too. Trilobites - meaning three lobes or parts - had very advanced eyes, and some even walked along the sea floor instead of swimming.

**What plants were on Earth****during the Cambrian Period****?**
                            - Many types of algae lived in the ocean.
                            - Land plants had not yet evolved.

**What was Virginia like****during the Cambrian Period****?**
                            - All of Virginia was under water during the Cambrian!
                            - The sediments from that sea are limestones, shales, and sandstones today.

 

### The Ordovician Period: 485 to 444 million years ago

**What did Earth look like during the Ordovician Period?**

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                            - Most continents were still part of the supercontinent Gondwana.
                            - North America and northern Europe were slowly moving toward each other.
                            - Near the end of the Ordovician, the part of Gondwana that is northern Africa today moved over the South Pole, triggering an ice age.
                            - When more of Earth’s water is frozen in glaciers, less water fills the oceans and sea level drops. The massive glaciers that formed on proto-Africa caused sea level to drop, emptying many of the shallow seas that surrounded the continents. 

**What was Earth’s climate like****during the Ordovician Period****?**
                            - Warm and wet like the Cambrian until near the end of the Ordovician.
                            - Then, the climate got much colder and an ice age began.

**What animals were on Earth****during the Ordovician Period****?**
                            - Trilobites and crinoids were still around.
                            - Many new marine invertebrates with shells evolved at this time and replaced Cambrian forms.
                            - The first corals appeared, but they were not widespread.
                            - Algae and sponges dominated reefs.
                            - Jawless, armored fish were common.
                            - KIDS’ CORNER:  Is that an octopus in a pointy tube swimming toward me? Not really, but this animal was a type of cephalopod, which is in the same group as octopi. This nautiloid, known as Orthoceras is extinct today, but would have propelled itself toward you quickly by sucking in water at one end and squeezing it out at the other.

**What plants were on Earth****during the Ordovician Period****?**
                            - The first land plants appeared.
                            - They were similar to mosses and other plants without deep roots or leaves.

**What was Virginia like****during the Ordovician Period****?**
                            - Near the end of this period, North America and northern Europe collided, forming the Taconic Mountains north of Virginia.
                            - The mountains eventually eroded, sending large amounts of sediment into the shallow sea that later solidified into sedimentary rocks (shales and sandstones).
                            - Later, these sedimentary rocks rose above sea level in what is now Virginia.

**What else happened****during the Ordovician Period****?**
                            - A MASS EXTINCTION ended the Ordovician Period when ~80% of species living in the shallow seas became extinct!
                            - Abundant glaciers caused sea level to drop.

 

### The Silurian Period: 444 to 419 million years ago

**What did Earth look like during the Silurian Period?**

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                            - Gondwana started moving away from the South Pole.
                            - North America and northern Europe had collided.

**What was Earth’s climate like****during the Silurian Period****?**
                            - As Gondwana moved away from the South Pole, many of the glaciers melted, and the ice age ended.
                            - The climate was similar to today’s, with cold weather and glaciers near the South Pole and warmer weather near the equator.
                            - There was a significant increase in sea level from the melted ice, resulting in the reappearance of many shallow seas.

**What animals were on Earth****during the Silurian Period****?**
                            - Large coral reefs first appeared, and they were common in tropical shallow seas.
                            - There was significant evolution in the jawless fishes, and some species lived in brackish waters.
                            - The first fish with jaws appeared.
                            - The first evidence for animals on land occurred in the Silurian: scorpions and millipede-like animals.

 

 

**What plants were on Earth****during the Silurian Period****?**
                            - The first vascular plants (with veins for transporting liquids) appeared, but they were very small.
                            - Once these land plants appeared, they rapidly covered most of the land surface.

**What was Virginia like****during the Silurian Period****?**
                            - Large amounts of sediment continued to erode off the Taconic Mountains to the northeast.
                            - These sediments settled to the bottom of a sea to form the sandstones we find in VA today.

 

### The Devonian Period: 419 to 359 million years ago

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**What did Earth look like during the Devonian Period?**
                            - At the beginning of the Devonian, there were three major continental masses.
                            - The North America/Europe continent was near the equator.
                            - To the north was a portion of modern Siberia, and Gondwana dominated the Southern Hemisphere.
                            - During the Devonian, all three continents were moving toward each other.
                            - Sea level was high, and much of what is land today was under shallow seas.   

**What was Earth’s climate like****during the Devonian Period****?**
                            - Because so much of the land was near the equator, the climate was warm and mild; it was a greenhouse age.
                            - The interiors of the large continents were dry, and salt and gypsum deposits formed.

**What animals were on Earth****during the Devonian Period****?**
                            - The shallow, tropical seas had abundant reefs and were home to a myriad of sea life.
                            - Sharks became common at this time.
                            - The first lobe-finned fish evolved early in the Devonian, and by the end of the Devonian had evolved into the first amphibian-like animals.
                            - These proto-amphibians were the very first vertebrates to inhabit the land. 
                            - The oldest preserved insects and centipedes appeared in the Devonian.
                            - Trilobites were declining, and this may have been due to an increase in swimming predators.

**What plants were on Earth****during the Devonian Period****?**
                            - By the end of the Devonian, the first trees and the forests were present. 
                            - Ferns and seed-producing plants also first evolved in the Late Devonian.
                            - No flowering plants existed.
                            - Because of the great increase in land plant debris, the first loamy soils, ideal for plant growth, were formed.

**What was Virginia like****during the Devonian Period****?**
                            - To the north, the Acadian Mountains were pushed up, and fine sediments from the erosion of these mountains flowed into Virginia, which was still underwater, forming the shales we find today.

 

### The Carboniferous: 359 to 299 million years ago

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The Carboniferous Period is often further divided into two different periods - The Mississippian Period (early Carboniferous) and the Pennsylvanian Period (late Carboniferous).

The Carboniferous has a clue in its name – CARBON – and this is when much of Earth’s carbon-rich coals formed because many places on Earth were swampy.

**What did Earth look like during the Carboniferous?**
                            - The continent of Gondwana moved close enough to the North America/Europe continent to cause initial uplift of the Appalachian Mountains.
                            - Their eventual continental collision created the super continent Pangaea by the beginning of the Permian Period. 

**What was Earth’s climate like?**
                            - The early part of the Carboniferous had a uniform, tropical, wet climate with little seasonality.
                            - As part of Gondwana reached the South Pole, a major ice age began. 
                            - There were alternating glacial periods when vast ice sheets covered much of Gondwana and nonglacial times when much of the ice melted.
                            - This caused repeated major changes in sea level.
                            - Land near the equator always stayed moist and tropical.

**What animals were on Earth?**
                            - The shallow seas surrounding each continent retreated as the continents approached each other and as the ice ages caused periodic lowering of sea level.
                            - With the loss of these seas, many of the shallow marine organisms disappeared.
                            - On land, the first reptiles appeared, and they laid the first shelled eggs.
                            - With this important evolutionary innovation, vertebrates no longer had to find water in which to lay their eggs.
                            - The first land snails and insects with wings appeared (i.e., dragonflies and mayflies), and some of these had wingspans of more than three feet!
                            - KIDS’ CORNER: Giant dragonflies!

**What plants were on Earth?**
                            - Forests were widespread near the equator.
                            - Lush plant growth provided the raw material for the great coal deposits of the world.
                            - The first conifers appeared during the Carboniferous. 

**What was Virginia like?**
                            - The area that will become Virginia was now on land where it was tropical and swampy.
                            - Thick layers of plant detritus filled shallow swamps, eventually forming the coal deposits we see today.
                            - The Appalachian Mountains began to rise.

 

### The Permian Period: 299 to 252 million years ago

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**What did Earth look like****during the Permian Period****?**
                            - Pangaea now existed as a super continent that contained almost all the land area of the world.
                            - This continent stretched from the North Pole to the South Pole and was the largest land mass since before the Cambrian Period.
                            - Once again, there was an ice sheet at the South Pole.
                            - There were fewer shallow seas than during the Carboniferous Period.

**What was Earth’s climate like during the Permian Period?**
                            - With all the landmass now in one giant continent, there were huge climatic changes.
                            - Because there were no moderating effects from nearby water bodies, vast deserts formed in the central region of Pangaea.
                            - These deserts had great daily and seasonal temperature changes, perhaps greater than anything we see on the planet today. 
                            - The drier climate doomed the mighty coal swamps of the Carboniferous.
                            - There was a wide latitudinal variation in climate with glaciers at the poles and tropical vegetation at the equator.   

**What animals were on Earth during the Permian Period?**
                            - Shallow coastal seas continued to decrease in size, so habitats for shallow marine organisms also decreased..
                            - As many swamps dried up, amphibian populations dwindled.
                            - Reptiles diversified and spread across the land.
                            - The precursors to mammals evolved.

**What plants were on Earth during the Permian Period?**
                            - As Pangaea became more arid and seasonal, most of the tropical coal swamps disappeared.
                            - Swamps were replaced by temperate forests that contained abundant conifers.

**What was Virginia like during the Permian Period?**
                            - Some coal swamps continued to exist in Virginia, and there was continued uplift of the Appalachian Mountains.

**What else happened during the Permian Period?**
                            - The LARGEST MASS EXTINCTION of life on our planet occurred at the end of the Permian when ~ 96% of all species perished.
                            - Evidence suggests that massive volcanic eruptions, one or more meteor impacts, and/or a rapid temperature increase due to a sudden release of methane from the ocean bottoms may have contributed to this extinction.  

Onward to the Mesozoic!

Backward to the Introduction