Question

The earliest fossils of vascular plants were formed during the _______ period. a. Ordovician b. Silurian c. Devonian d. Triassic e. Jurassic

Short answer

The earliest fossils of vascular plants were formed during the Silurian period.

Step-by-step solution

Understanding Geological Time scales

Different geological periods, from the Proterozoic Eon to the Phanerozoic Eon, contain rich fossil records that provide information about plant life in those periods.

Understanding Plant Evolution

Vascular plants, which are land plants that have lignified tissues for conducting water and minerals throughout the plant, first evolved during a specific period. The key is to identify this correct period.

Identifying the Correct Period

Among the options given, the Silurian period is known to be the time when the first vascular plants, specifically the Cooksonia, appeared.

Key concepts

Geological Time Scales

The Earth's history is divided into a series of chronological divisions known as geological time scales. These scales represent periods of time defined by significant geological or paleontological events, like the emergence of new forms of life or mass extinctions. The largest divisions of time are eons, followed by eras, periods, epochs, and ages. Understanding these scales is essential for studying the history of life on Earth, including plant evolution.

Within these scales, the fossil records serve as a historical archive, allowing scientists to piece together the story of Earth's past. By examining rock layers and the fossils within them, geologists and paleontologists can discern what the world was like at various points in its 4.6-billion-year history. The knowledge of which organisms existed and how they changed over time provides a window into evolutionary processes.

Plant Evolution

Plant evolution is a fascinating journey that spans over hundreds of millions of years. Initially, life was confined to the oceans, but over time, plants made the colossal leap to colonize land. This transition involved the development of several critical adaptations such as roots, stems, leaves, and notably, vascular tissues.

Vascular plants, or tracheophytes, are distinguished by their lignified tissues called xylem and phloem. These specialized structures enable the efficient transport of water, minerals, and sugars throughout the plant, which is essential for survival on land. The earliest vascular plants had to overcome numerous challenges, including desiccation and the support against gravity. Throughout plant evolution, these essential traits became more complex, leading to the rich diversity of plant life we see today.

Silurian Period

The Silurian period, which lasted from approximately 443.8 million to 419.2 million years ago, is a significant chapter in the Earth's history for plant evolution. It came after the Ordovician period and before the Devonian period. During the Silurian, Earth experienced considerable changes that set the stage for major evolutionary advancements. One of the most noteworthy events was the appearance of the earliest known vascular plants.

Notable Silurian Plants

Cooksonia, often considered the earliest known vascular plant, is our best evidence of plant life from this era. Its simple structure lacked true leaves and roots but had stems with vascular tissues, representing a major evolutionary step. The colonization of land by plants during the Silurian had profound effects on the planet, including influencing the climate and soil development, and paving the way for subsequent terrestrial ecosystems to evolve.