The Web of Life (20-7) Evolutionary Effects

 Evolutionary Effects

As a consequence of continental drift, biotas once together come apart or vice versa. This drives evolution, though the tectonic dynamic is on a much longer time scale than other factors more immediately affecting life: the landscape (including volcanic activity), atmosphere, and oceans – elements which influence climate as a demanding evolutionary impetus. Still, from an evolutionary perspective, tectonics and climate are 2 of most influential geophysical forces for the prospects of life on Earth. Though global climate may gyrate without land masses moving, tectonic changes have invariably caused major shifts of climate.

0.8 to 0.5 BYA, the planet experienced an extraordinary epoch, termed Snowball Earth, featuring 3 episodes of near-global glaciations. Thanks to the anomalous behavior of water, the planet was able to break its frozen grip.

Unlike most molecules, water’s solid phase is less dense than its liquid phase. If ice did not float, the oceans would have frozen from the bottom up, with the world long locked in ice.

Lacking sufficient mass of photosynthetic organisms to soak up all the atmospheric carbon dioxide from volcanic emissions, an energetic greenhouse effect developed, resulting in rapid melting. Volcanoes sated the seas with helpful chemicals, including phosphate. In the wake of Snowball Earth multicellular organisms proliferated.

Beyond tectonics (including volcanism) and climate, another major impact on life has been bolides. Though the age of dinosaurs was coming to a close on some continents due to tectonic shifts, the end was hastened by a strike from space.

Mammals began to thrive when biomes were particularly fragmented. Relative isolation from dinosaur dominion allowed a new evolutionary lineage to emerge.

Old and New World monkeys came from the same stock but followed independent paths as South America and Africa drifted apart some 50 MYA. The marsupial mammals of Australia evolved in isolation from placental mammals as the island continent drifted out to sea more than 60 MYA.

India crashed into Asia 45 MYA, creating the Himalayas, and inciting an exchange of life. Africa and Eurasia made contact 18 MYA. Primates joined other species making a south-to-north migration, while many antelope species moved the other way.

The Americas came together ~3 MYA at the Panamanian Isthmus, facilitating an exchange of species that had evolved separately for millions of years. This was the Great American Interchange.