During the Devonian period, the colonization of continental landmasses by early vascular plants dramatically altered the Earth's geosphere. Prior to this botanical invasion, terrestrial surfaces consisted largely of barren rock and primitive microbial crusts, which exerted minimal chemical influence on their substrates. The advent of deep, complex root systems, particularly those of progymnosperms like Archaeopteris, fundamentally changed this dynamic. These extensive root networks physically shattered bedrock and secreted organic acids, which vastly accelerated the rate of silicate weathering. Because the chemical weathering of silicate minerals consumes carbon dioxide from the atmosphere, this biological acceleration precipitated a significant drawdown of global carbon dioxide levels. Consequently, the greenhouse effect weakened, plunging the planet into a series of intense glacial episodes. At the same time, the massive influx of weathered nutrients and organic debris washed into marine environments, triggering widespread eutrophication. This nutrient overload fueled massive algal blooms, the subsequent decomposition of which depleted dissolved oxygen, culminating in catastrophic marine anoxia and the Late Devonian extinction event.
Based on the passage, in what order do the events occurring during the Devonian period causally lead to the onset of global cooling?
- 1Terrestrial colonization by early vascular plants and the development of deep, complex root systems
- 2Physical fracturing of bedrock and secretion of organic acids that accelerate silicate weathering
- 3Consumption and depletion of atmospheric carbon dioxide through the chemical weathering of silicate minerals
- 4Weakening of the greenhouse effect and the onset of intense global glacial episodes