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| Giant armadillos (glyptodonts), Doedicurus clavicaudatus Credit: © Peter Schouten |
Recent findings by scientists from the Universities of Arizona, Wyoming and Connecticut, give a fascinating insight into how Earth's ecosystems are dynamic, and how evolution is an integral part of how the system works to maintain itself, without the need for magic or interference.
The researchers, led by Barbara Carrapa, professor and head of the UA Department of Geosciences, showed that there was a major change in the climate of South America between 7 and 6 million years ago, caused by a change in the global tropical atmospheric circulation known as the Hadley circulation. The result was that South America became drier allowing subtropical grasslands to expand.
This expansion of grasslands resulted in the evolution of several species of mammal that could eat grass, and to the evolution of both high-crowned and ever-growing teeth in response to the wear from eating grass with a high silica content.
Using computer modelling to simulate climate change based on atmospheric CO2 and ocean surface temperature and the resulting soil chemistry, they team found a high degree of correlation between the predicted soil chemistry and the actual soil chemistry for an intensification of the Hadley circulation. The paleontological record closely matched the predicted expansion of grasslands.
The team's findings were published in Proceedings of the National Academy of Science a few days ago.
Significance
This paper analyzes the Late Miocene continental record of hydroclimate from the central Andes and subsequent ecological response to climatic change during this interval. The Late Miocene cooling (LMC) is characterized by a sharp decrease (up to 6 °C) of sea-surface temperatures and has been shown to have driven ecosystem reorganization, leading to conditions similar to Quaternary. We use the stable isotopic record preserved in pedogenic carbonate nodules as a proxy for hydroclimate changes during the LMC. This, combined with general circulation simulations, shows that strengthening of the Hadley circulation in South America during the LMC enhanced subtropical aridification and in turn promoted expansion of C4 grasses and evolution of high-crowned teeth in mammals.
Abstract
Near-modern ecosystems were established as a result of rapid ecological adaptation and climate change in the Late Miocene. On land, Late Miocene aridification spread in tandem with expansion of open habitats including C4 grassland ecosystems. Proxy records for the central Andes spanning the Late Miocene cooling (LMC) show the reorganization of subtropical ecosystems and hydroclimate in South America between 15 and 35°S. Continental pedogenic carbonates preserved in Neogene basins record a general increase of δ18O and δ13C values from pre-LMC to post-LMC, most robustly occurring in the subtropics (25 to 30°S), suggesting aridification and a shift toward a more C4-plant-dominated ecosystem. These changes are closely tied to the enhancement of the Hadley circulation and moisture divergence away from the subtropics toward the Intertropical Convergence Zone as revealed by climate model simulations with prescribed sea-surface temperatures (SSTs) reflecting different magnitudes of LMC steepening of equator-to-pole temperature gradient and CO2 decline.
So, changes in atmospheric CO2 and ocean surface temperature 6-7 million years ago ended up creating an environment in which mammals evolved with teeth specialised for eating grass, and in which ancient armadillos the size of a small car came to exist. This is a perfectly rational process, easily-understood by anyone but those determined not to understand it. It does not require magic or intelligent intervention. In fact, if we consider the steps needed by any designer of such an outcome, it becomes absurd in the extreme.
Firstly, a designer would need to replace an existing ecosystem with all its species and climate with a new one consisting of grasslands and a different climate with ocean currents and temperature to maintain the new weather pattern, then design new species so they could eat the grass, complete with special teeth because the teeth it had designed earlier aren't very good for eating grass which it designed with a high silica content that wears teeth down.
And for what purpose? In what way was this new ecosystem objectively better than the previous one? Any religious explanation based on the notion that it was all for humans can be discounted because there weren't humans in South America 6 million years ago.
All that complexity; all that waste and all for no discernable purpose. Creationists consider this the work of an intelligent designer.
Biologists see it as the work of natural, dynamic, undirected processes occurring on a dynamic planet. Biologists have evidence for their explanation, such as that presented here. Creationists have the guesses of pre-wheel Bronze Age subsistence farmers. Tweet
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