Question

The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. What was the Earth's land surface like during the early Paleozoic? (E)

Short answer

During the early Paleozoic era, Earth's land surface was predominantly composed of the supercontinent Gondwana, which consisted of present-day Africa, South America, Antarctica, India, and Australia. The landscape was mostly barren initially, with simple terrestrial plants beginning to evolve by the end of the Silurian period. The climate fluctuated due to continental drifts, with periods of warm, tropical temperatures and glaciations that influenced the distribution of ice caps.

Step-by-step solution

Introduction to the Paleozoic Era

The Paleozoic Era spans from approximately 542 to 250 million years ago. It is divided into six distinct geological periods: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. The early Paleozoic refers to the Cambrian, Ordovician, and Silurian periods.

Cambrian Period (542-485 million years ago)

During the Cambrian period, the Earth's land area was mostly limited to a single supercontinent, named Gondwana. Gondwana consisted of present-day Africa, South America, Antarctica, India, and Australia. The overall landscape was prevalently barren, as terrestrial plants had not yet evolved. The climate during this time was warm and tropical, with no polar ice caps.

Ordovician Period (485-444 million years ago)

In the Ordovician period, the Gondwana supercontinent still dominated the land surface, but it started drifting towards the South Pole. Around the end of the Ordovician, the first primitive plants started to appear on the surface. The glaciations occurred during this period, resulting in a widespread ice age, with much of Gondwana covered by ice caps.

Silurian Period (444-419 million years ago)

During the Silurian period, Gondwana shifted further towards the southern hemisphere. Many of the Earth's other landmasses started to approach one another, eventually forming the supercontinent named Laurussia or Euramerica. The Silurian period witnessed an increase in the variety of land vegetation with the beginning of simple vascular plants that could transport water and nutrients throughout their tissues. The climate became warmer and tropical, with a relatively shallow ocean covering large parts of the continental crust. To sum up, the early Paleozoic Earth's surface was primarily made up of the supercontinent Gondwana, shifting towards the South Pole. The landscape was mostly barren in the beginning, and simple terrestrial plants began to evolve by the end of the Silurian period. Climate changes associated with continental drifts influenced the distribution of ice caps and the overall temperature of the environment.

Key concepts

Cambrian Period

The Cambrian Period was a groundbreaking chapter in Earth's geological history, stretching from about 542 to 485 million years ago. This period is notable for the "Cambrian Explosion," an event where there was a rapid increase in the diversity of life forms.
During this time, the Earth's land was mostly under the control of a vast supercontinent known as Gondwana. This massive landmass included parts of what we know today as Africa, South America, Antarctica, India, and Australia.
The surface of Gondwana was largely barren, with no significant plant life covering the land. At this stage, life was primarily aquatic. There were no land plants yet as terrestrial vegetation was not evolved. The environment was mostly warm and tropical, with no ice caps at the poles.

• No polar ice caps and a warm climate.
• Vast underwater biodiversity due to the Cambrian Explosion.
• Barren terrestrial landscapes on Gondwana.

These conditions set the stage for many of the unique life forms that defined this period and paved the way for more complex ecosystems in the future.

Ordovician Period

Following the Cambrian, the Ordovician Period, lasting from approximately 485 to 444 million years ago, saw significant geological and biological changes. Gondwana began to drift towards the South Pole, and the Earth experienced some of its first widespread glaciations.
This period marked the first emergence of simple, primitive plants on land. These plants laid the evolutionary groundwork for more complex land vegetation that would develop in later periods.
Despite the cold glacial conditions later in the Ordovician, the early part of the period still enjoyed warm tropical climates. This time saw an increase in biodiversity, particularly in marine environments.

• End-Ordovician glaciation and ice ages.
• Introduction of primitive terrestrial plants.
• Continual drift of Gondwana towards the South Pole.

The shift towards colder climates played a significant role in shaping the Earth's biological and geological landscape.

Silurian Period

The Silurian Period, ranging from about 444 to 419 million years ago, continued the transitions begun earlier, seeing further diversification of life on Earth. Gondwana remained in the southern hemisphere, edging closer to fully shifting south.
One of the key developments of the Silurian Period was the evolution and spread of the first vascular plants, which were more complex than their predecessors. These plants were capable of transporting water and nutrients throughout their structures, allowing them to colonize new areas.
Geologically, during this time, other landmasses started to drift together, forming a new supercontinent known as Laurussia or Euramerica. This played a crucial role in the shifting climatic patterns and sea levels.

• Rise of simple vascular land plants.
• Formation of Laurussia supercontinent.
• Climate warmed again, leading to mostly tropical environments.

The Silurian period set the foundation for complex land ecosystems and was a pivotal time of change and adaptation for life on Earth.