Problem 17 - Biology

Question

Plant life first appeared on land during which of the following periods? a. Cambrian period b. Ordovician period c. Silurian period d. Devonian period

Step-by-Step Solution

Answer

c. Silurian period

Step 1 - Understanding the Question

Determine which period is known for the first appearance of plant life on land. Review the given options: Cambrian, Ordovician, Silurian, and Devonian periods.

Step 2 - Reviewing Geologic Time Periods

Understand the characteristics of each period: - Cambrian period: Known for the Cambrian Explosion, with a variety of marine life. - Ordovician period: Marine algae and the first evidence of land plants as spores. - Silurian period: More robust evidence of plant life developing on land. - Devonian period: Known as the Age of Fishes, but also had significant plant diversification.

Step 3 - Narrowing Down the Options

From these periods, pinpoint the specific period known for the first substantial plant life evidence on land. The Ordovician period has initial signs of spores, while the Silurian period shows substantial development of land plants.

Step 4 - Conclusion

Silurian period is recognized for more robust evidence of the development of vascular plants. Thus, the first significant appearance of plant life on land is in the Silurian period.

Key Concepts

geologic time periods

To understand when plant life first appeared on land, it's crucial to grasp the concept of geologic time periods. Geologic time is divided into a series of eons, eras, periods, epochs, and ages that help scientists communicate about Earth's history.
These time divisions help us understand the sequences and timing of events that have occurred over Earth's 4.6 billion-year history.

• **Eons** are the largest time intervals and include numerous eras. The Phanerozoic Eon, for example, covers the time from roughly 541 million years ago to the present.
• **Eras** break down eons further. The Phanerozoic Eon includes the Paleozoic, Mesozoic, and Cenozoic eras.
• **Periods** are subdivisions of eras. Our focus includes the periods: Cambrian, Ordovician, Silurian, and Devonian.

Understanding these periods is essential to pinpoint when terrestrial plant life began its journey on Earth.

Cambrian period

The Cambrian period spanned from about 541 to 485 million years ago. It is primarily known for the Cambrian Explosion—a remarkable burst of evolutionary activity resulting in the appearance of various marine organisms.
The seas teemed with life, including trilobites, brachiopods, and the first primitive vertebrates.
However, terrestrial environments during this period were barren due to a lack of substantial plant life.
In summary, the Cambrian period marked a significant development in marine biodiversity but recorded no evidence of plant life colonizing land.

Ordovician period

The Ordovician period lasted from around 485 to 444 million years ago. While the oceans continued to diversify with marine life, something important happened on land.
The earliest evidence of land plants came in the form of spores, indicating that some algae and early plants were beginning to adapt to terrestrial environments. These early plants were likely non-vascular, meaning they lacked true roots, stems, and leaves.
The appearance of these spores is a critical step in understanding the transition of life from water to land.

Silurian period

The Silurian period, occurring between 444 and 419 million years ago, brings us closer to the stage where plant life firmly established itself on land.
This period is particularly significant because it offers more robust evidence of terrestrial vegetation. Vascular plants, which have specialized tissues for transporting water and nutrients, began to appear. These early vascular plants included simple forms such as cooksonia.
With vascular systems, plants could grow taller and inhabit a broader range of environments, which paved the way for more complex ecosystems.

Devonian period

The Devonian period, from about 419 to 359 million years ago, is often called the Age of Fishes due to the diversity and dominance of fish in aquatic ecosystems.
However, this period also saw significant advances in plant life. Plants began to develop more complex structures, including leaves and roots, and grew into sizeable forests.
This period marks an increase in plant diversity and complexity, leading to the formation of the first forests. It’s a critical era for understanding how terrestrial ecosystems as we know them began to take shape.
Although the first substantial evidence of terrestrial plant life appeared in the Silurian period, the Devonian period showcases their evolution and establishment.