For a significant portion of its long history, Earth’s landmasses existed without trees. This treeless past meant the planet’s appearance and its ecosystems were profoundly different from the forest-dominated world we know today. Without trees, the terrestrial environment was shaped by different forces and hosted distinct forms of life.
The Ancient Eras of Treeless Earth
Earth’s land remained largely treeless for billions of years, with true trees emerging relatively late in geological time. The initial colonization of land by plants began around 460 million years ago, during the Ordovician period. While early non-vascular plants like mosses and liverworts appeared, they lacked the structural complexity to grow tall.
The Silurian period (443 to 419 million years ago) saw the evolution of the first vascular plants. These plants possessed internal systems for water transport, allowing them to grow more upright, though they remained small. Only towards the end of the Devonian period (around 358 million years ago) did plants evolve woody tissue and true roots, leading to the development of the first forests. This means that for vast stretches of the Precambrian, Cambrian, Ordovician, Silurian, and most of the Devonian periods, Earth’s land was devoid of anything resembling a tree.
The Ground Cover: Early Terrestrial Life
During treeless eras, Earth’s land was not entirely barren but covered by low-lying life forms. Non-vascular plants, such as mosses and liverworts, formed sprawling, carpet-like growths, often thriving in wet environments due to their lack of internal water transport. Early vascular plants, like Cooksonia and rhyniophytes, were also present, characterized by simple, leafless stems and growing only a few centimeters tall. These plants reproduced by spores, and their structures did not differentiate into true leaves, stems, or roots.
Lichens and various fungi played significant roles in colonizing the land. Some fungi, particularly Prototaxites, grew to immense sizes, resembling massive spires or columns. These towering organisms, existing between 420 and 350 million years ago, were the tallest living things on land during their time. Microbial mats, composed of cyanobacteria and algae, also formed widespread coverings, especially in damp areas, contributing to early terrestrial ecosystems.
The Barren and Alien Landscapes
Earth’s landscapes looked strikingly different without trees. Vast, open expanses of bare rock, sand, and mudflats dominated the terrestrial environment. Without extensive root systems to bind the soil, wind and water erosion were significant forces shaping the land. The color palette was dominated by browns, grays, and reddish hues from exposed minerals and sediments.
Microbial mats, mosses, liverworts, and early vascular plants formed low-lying carpets, creating a relatively flat ground cover that lacked the vertical complexity of modern forests. The presence of giant Prototaxites added an unusual element, standing as solitary, enormous columns across the landscape. This open terrain extended for vast distances, punctuated by these towering fungal structures or low-lying vegetation.
Atmospheric and Climatic Conditions
Atmospheric and climatic conditions on a treeless Earth differed considerably from present-day conditions. Before significant land plant colonization, atmospheric carbon dioxide levels were extremely high. As land plants evolved, they contributed to a decrease in atmospheric carbon dioxide and an increase in oxygen levels. This shift in atmospheric composition influenced global cooling trends.
The absence of widespread forests meant different rainfall patterns, as trees influence local weather systems through evapotranspiration. Land surfaces experienced increased exposure to solar radiation without widespread shade. Wind erosion was more prevalent across the open landscapes, affecting soil formation and sediment distribution. The emergence of land plants had a profound impact on Earth’s atmosphere, water cycle, and climate, gradually transforming the planet over millions of years.