Paleozoic Era Timeline
The Paleozoic Era began about 541 million years ago and lasted till 251.9 million years ago. It was the first era of the Phanerozoic Eon and is otherwise known as the “Age of Ancient Life.” The other two eras that follow this are the Mesozoic (age of middle life) and the Cenozoic (age of recent life). The Precambrian Eon predates the Paleozoic. The era is further divided into geologic periods marked by major changes in Earth’s geology, climate, and lifeforms.
Cambrian Period — 542 to 485.4 Million Years Ago
This was the first period of the Paleozoic Era and Phanerozoic Eon. It was a significant time in geologic history because it was characterized by major changes in the types of living organisms on Earth. Prior to this time, the living organisms on Earth were mostly small unicellular animals. The Cambrian explosion occurred at the beginning of this period, giving rise to complex multicellular animals.
Ordovician Period — 485.4 to 443.8 Million Years Ago
The Ordovician Period is characterized by notable changes in Earth’s geology and climate. Some of the Earth’s highest peaks, like Mount Everest, were formed during this period. The rapid spreading of the seafloor not only gave rise to the formation of new rocks but also caused major flooding as the sea level rose. North America was almost entirely underwater at the time. The global flood allowed the deposition of sedimentary rocks and supported the preservation of several fossils of marine animals. The Ordovician Period ended with an extinction event known as the Late Ordovician mass extinction.
Silurian Period — 443.8 to 419.2 Million Years Ago
This was the shortest period in the Paleozoic Era. It saw high sea levels because the glaciers formed during the Ordovician ice age started melting. Since the Ordovician Period had ended with an extinction event, the Silurian was characterized by a gradual recovery of marine and terrestrial life.
Devonian Period — 419.2 to 358.9 Million Years Ago
The Devonian Period had more dry lands, and vascular plants thrived because of this. Scientists often refer to the Devonian as the “Age of Fishes” because there were diverse creatures in the Devonian seas, and they were quite abundant in their numbers. Also, receding seas allowed the first seed-bearing plants to appear on land. Later during this period, vertebrates such as four-legged amphibians started to come on land.
Carboniferous Period — 368.9 to 298.8 Million Years Ago
This was the longest period in the Paleozoic Era. It is also known as the “coal-bearing period” because of the coal beds formed globally during this time. More terrestrial animals also arrived on the scene during this period. The Carboniferous Period is commonly called the “age of the amphibians” because amphibians became the dominant land vertebrates. Insects were also quite widespread. During the latter half of the period, the Carboniferous forest system collapsed, and another ice age occurred. The Earth’s continents also collided to form the supercontinent Pangaea.
Permian Period — 298.9 to 252.2 Million Years Ago
This was the last period in the Paleozoic Era. It is most notable for the largest mass extinction on Earth and wiped out 81% of marine species and about 70% of terrestrial species. The effects of the catastrophic event were so powerful that it took the planet 30 million years to recover. Before this time, life on Earth had made significant progress, with insects evolving into new habitats and new reptile lineages appearing. The Earth gradually warmed up during the Permian, which probably contributed to the ecological crisis that occurred towards the end of that period.
The Paleozoic Climate
The climate in the early period of the Paleozoic was relatively moderate and stable. However, as the Cambrian Period went by, the climate grew warmer. In contrast, the marine environment became colder. The climate remained stable until the ice age at the end of the Ordovician Period. The mid-Paleozoic was considerably stable as the sea level had dropped and the Ordovician ice had melted. During the Devonian, plants found more ground, resulting in warmer climates as the carbon dioxide level dropped and oxygen level rose. This continued until the early Carboniferous Period as the carbon dioxide level continued to decline. The low level of carbon dioxide destabilized the climate, causing another round of ice age. After this period, the Paleozoic climate experienced temperature extremes until the Permian extinction.
The Paleozoic Geography
The Paleozoic Era is also characterized by major changes in the Earth’s geology. The continents as we currently know them formed gradually over the course of the Paleozoic Era. At the beginning of the era, the supercontinent Pannotia was just starting to break up as a global ice age was ending. The massive single landmass broke up into relatively smaller continents that drifted away from each other. As the era progressed, the continents of Africa and South America on the west joined with Madagascar, India, Antarctica, and Australia on the east to form a single landmass known as Gondwanaland. Scientists studying the plant life of the Paleozoic Era discovered that the plant life on the southern continents remained distinct from those in North America until the Devonian Period. This suggests that North America collided with Gondwana around this period. From that point forward, the fauna became quite similar. The formation of a new supercontinent (Pangea) finally became complete during the Permian when the landmass of southern South America, western Antarctica, and New Zealand collided with Gondwana. With Pangaea fully formed, the shallow seas of the Paleozoic Era retreated from the continents.
Paleozoic Life
As mentioned earlier, the early Paleozoic Era was characterized by marine life alone. At the start, life on Earth mainly consisted of simple unicellular and complex multicellular organisms in the form of bacteria, algae, and sponges. Given the nature of these early Cambrian organisms, there was little or no fossil evidence from this period. The Cambrian explosion, also known as the biological Big Bang, gave rise to about 35 new animal phyla. These were mainly marine animals whose fossils are abundant in Cambrian rock. Invertebrates were the dominant life form until the mid-Paleozoic. The Devonian is called the “Age of Fishes” because this was when fishes evolved. Around this time, leafless vascular plants also began to form on land. The transition of life from the marine to terrestrial habitat also occurred during the Devonian Period as more land amphibians came on the scene. By the Carboniferous Period, plants and animals were less dependent on water or moist areas for living; seed plants replaced water-borne spores. Life broke away from the oceans fully as the evolution of the amphibians paved the way for the emergence of reptiles. This period also saw the evolution of flight animals. These were insects with wings, such as mayflies and dragonflies. The Permian extinction, which occurred at the end of the Paleozoic Era, wiped out up to 90% of all species on Earth at the time. The global extinction event set the stage for the next event in Earth’s history.
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