Section 1.1: The Ordovician Period (485 to 443 million years ago)

Diversification

During this period, Gondwana emerged as the predominant landmass—not quite a supercontinent due to the presence of northern islands, but substantial nonetheless, encompassing much of the modern southern hemisphere. Meanwhile, evolution thrived in the oceans.

If the Cambrian Period marked the appearance of various body structures, the Ordovician was significant for the diversification of species, a phenomenon grandly termed the Great Ordovician Biodiversification Event. This era saw the rise of modern clams, snails, octopuses, and the first coral reefs.

The Advent of Land Plants

However, the hallmark of the Ordovician was the introduction of terrestrial plants. While the initial colonizers were modest mosses and liverworts, they represented the first steps toward greening our planet.

Sadly, the Ordovician period met a grim end due to a severe extinction event.

Extinction Event

Approximately 445 million years ago, Earth faced another glaciation, known as the Hirnantian, which proved catastrophic, annihilating 60% to 85% of all species. This extinction ranks among the most severe in Earth's history, second only to one other event.

The geography of Gondwana played a crucial role in this devastation. Typically, when climate shifts occur, flora and fauna can migrate to suitable climates. However, with Gondwana situated around the southern pole, its entire coastline shared the same latitude. When temperatures drastically dropped, there were no alternative habitats for the species, leading to their demise and the end of the Ordovician.

Section 1.2: The Silurian Period (443 to 419 million years ago)

Recovery Phase

As the ice sheets from the Hirnantian receded, sea levels surged to heights 100 to 200 meters above present levels, submerging coastal regions. The brief Silurian Period was marked by Earth's recovery, striving to regain balance among the atmosphere, biosphere, and climate.

Despite uncertainties, evolution surged forward. The period witnessed the emergence of bony and jawed fish, as well as the first land dwellers, including millipedes, centipedes, and spiders.

Evolution of Land Plants

This era also saw significant advancements in terrestrial plants, with the introduction of ferns, horsetails, and conifers. These new plant forms contained lignin, a vital compound for structural integrity, allowing them to grow larger than the delicate mosses.

Fungi's Role in Evolution

Co-evolving alongside these new plants were fungi, which thrived in the thin soils. Fungi formed a mutualistic relationship with land plants, exchanging nutrients essential for terrestrial life. This symbiosis began in the Silurian and was crucial for the establishment of life on land.

In the late Silurian and early Devonian, one of the largest known organisms was a remarkable mushroom called Prototaxites, reaching heights of 8 meters and a trunk width of one meter, overshadowing all other terrestrial life. However, the reign of these giant fungi was brief as life on Earth began to accelerate rapidly.

This article is Part 43 in a series of 50 exploring Earth's history, with each installment detailing a 100-million-year epoch.

Video Insights

To gain deeper insights into the evolution of plants, fungi, and animals, watch the following video:

This video titled "The Evolution of Plants, Fungi and Animals | Tree of Life Ep 3" explores the intricate relationships among these life forms.

Additionally, to understand how plants significantly altered Earth's history, view this:

This video, "How Plants Changed Earth's History," delves into the transformative impact of plant life on our planet.

Click here for Part 42: CHANGE and Part 44: FISH AND COAL. If you wish to explore all articles in the series, please follow me.