Imagine the Antarctic glaciers extending over the whole Earth. Dating back to the early 1960s, scientists proposed just such a scenario, known as a “snowball Earth” hypotheses to explain various geological and geochemical data in the planet’s history.
According to the proposal, a snowball Earth could possibly form when the planet experiences periods of increased glaciation (or ice ages) due to variations in its orbit around the Sun. As Earth’s temperature drops, glaciers around the north and south poles begin to grow and spread toward the equator. Snow and ice reflect more sunlight than rock, vegetation, and water, causing a further decrease in the global climate. If the glaciers reach close enough to the equator, the increased cooling might result in the complete covering of Earth with glaciers.
During the Cryogenian geological period (850-630 million years ago), two extensive glaciations occurred which may have resulted in snowball Earth. Presumably, continued volcanic action produced enough greenhouse gas emissions to reverse these hypothesized snowball Earth conditions. A thick glacial covering would dramatically impact life on Earth. In fact, these two extensive glaciations immediately preceded the Cambrian Explosion. However, if an abundance of organic carbon sediments covers the ocean floors, then a mechanism exists to prevent snowball scenarios.
An article published in Nature describes the discovery of one preventive mechanism. As the global temperature decreases with the advance of the glaciers, the oceans dissolve more oxygen from the atmosphere. Consequently, this oxygen reacts with the buried organic carbon to produce carbon dioxide, which then enters the atmosphere. The resulting increase in greenhouse heating prevents the further advance of the glaciers.
Because abundant life has existed for about 3.5 to 3.8 billion years of Earth’s history, an ample supply of deep ocean organic carbon has always existed to prevent a snowball Earth. While the snowball Earth hypotheses remain debatable, they do highlight a few apologetic points.
A snowball Earth provides one more mechanism that can severely disrupt a planet’s capacity to support life.
Scientists continue to find evidence that Earth’s habitability relies on an intricate interplay of geological (glaciation), astronomical (variations in Earth’s orbit), and biological (abundant deep-ocean organic carbon remains) processes.
Both of these points attest to the difficulty, from a naturalistic perspective, of attaining conditions suitable for life. That Earth has remained habitable throughout most of its history comports well with the idea that a super-intelligent Designer fashioned Earth intending to fill it with life.