Scientific advances continue to demonstrate our improbable planet’s fine-tuned features. In a recent issue of Science, a team of scientists led by Francis Macdonald described another extraordinary feature of Earth’s plate tectonic activity.1 This feature must be fine-tuned for life to persist on Earth for as long as it has and the required fine-tuning poses yet another challenge to naturalistic explanations for the history of Earth’s life.
A Habitability Bottleneck
In the 1970s, chemist James Lovelock2 and microbiologist Lynn Margulis3 proposed the Gaia hypothesis, which asserts that life continuously manipulates its physical and chemical environment so as to extend the duration in which it can exist on a planet nearly indefinitely, without any need for intervention or guidance from a supernatural Being.2 Carl Sagan, Stephen Gould, and other atheistic and agnostic scientists enthusiastically promoted the Gaia hypothesis as a means for bolstering their own nontheistic explanations for the origin and history of life.
At the XVIIIth International Conference on the Origin of Life that Fazale Rana and I attended in July 2017, Charles Lineweaver and Aditya Chopra presented a serious challenge to the Gaia hypothesis that they called the Gaian bottleneck.4 The Gaian bottleneck is the scientific recognition that if life somehow emerges on a planet, “it only rarely evolves quickly enough to regulate greenhouse gases and albedo, thereby maintaining surface temperatures compatible with liquid water and habitability.”5 The Gaian bottleneck implies that a planet must be continuously inhabited to remain habitable and that life on a planet must change dramatically and rapidly (to a degree and at a rate that challenges naturalistic explanations) for there to be any hope of compensating for the increasing brightness of its host star.
While I agree with the Gaian bottleneck explanation, I believe that it is grossly understated. In my book, Improbable Planet, I posed a refutation of the Gaia hypothesis. I explained how only a Mind that precisely knows the future physics of the Sun, Earth, and Moon will know which life-forms to withdraw from Earth and when, and which life-forms to create and when so that the new life-forms perfectly compensate for the changed physics of the Sun, Moon, and Earth in order to maintain the surface temperature and atmospheric chemistry on Earth that life requires.6
I also explained in Improbable Planet that for life to exist for several billion years on a planet it takes that same supernatural Being’s ability to precisely and continuously control Earth’s tectonic activity.7 Habitability requires a combination of just-right life at just-right times, plus just-right tectonics at just-right times.
Silicate Weathering and Carbon Dioxide Removal
Macdonald’s team demonstrated that often only small areas of Earth’s surface account for most of the carbon dioxide that is removed from Earth’s atmosphere. For at least the past 543 million years (the Phanerozoic eon), silicate weathering has been the dominant process for carbon dioxide removal from the atmosphere. Water in the oceans reacts with seafloor basalts to form silicates. Silicates, being lighter than basalts, float above the basalts. If a planet’s liquid water ocean is shallow enough and if the chemical transformation of basalts into silicates occurs over a sufficiently long time period, silicate landmasses will appear above sea level. Once they do, rain falling on the exposed silicates acts as a catalyst whereby carbon dioxide in the atmosphere reacts with the exposed silicates to make silicon dioxide (sand) and carbonates.
The rate at which carbon dioxide is removed from the atmosphere to transform silicates into sand and carbonates depends on four factors:
- the percentage of Earth’s surface area comprised of silicate landmasses,
- the degree to which life on the exposed silicates breaks up the silicates to generate more silicate surface area,
- the degree of relief (steepness) of the continental landmasses, and
- the amount of rainfall on the continental landmasses
Macdonald’s team of planetary scientists pointed out that all four factors are enhanced when two or more tectonic plates at tropical latitudes collide to uplift oceanic crust to form a new exposed mountain range. Precipitation rates are usually higher in the tropics. Vegetation in the tropics typically is much denser. Thus, a new landmass with steep mountain slopes covered with dense vegetation receiving heavy rainfall can become a dominant contributor to carbon dioxide removal from Earth’s atmosphere. For example, today, just 9 percent of Earth’s landmass area accounts for half of the atmospheric carbon dioxide removed by silicate weathering.8
Macdonald and his colleagues showed that events where oceanic crust becomes uplifted to form exposed mountain ranges correlates with the four glaciation periods that have occurred during the Phanerozoic eon. These four are the Late Ordovician glaciation sometime between 455 and 440 million years ago, the Late Devonian glaciation about 360 million years ago, the Carboniferous-Permian glaciation sometime between 335 and 280 million years ago, and the glaciation that began about 8 million years ago and developed into the ice age cycle of the past 2.58 million years.9
In a recent blog, I wrote about how the especially hard collision between the Indian subcontinent tectonic plate and the Eurasian tectonic plate uplifted the seafloor between the Indian subcontinent and Asia to form the Himalayas and the Tibetan Plateau. In that blog I noted that silicate weathering (the conversion of silicates into sand and carbonates) of the Himalayas and the Himalayan foothills played a major role in lowering the carbon dioxide level in Earth’s atmosphere sufficiently to change the periodicity of the ice age cycle from 41,000 years to approximately 100,000 years.
Implications of Fine-Tuned Tectonics
These planetary scientists showed that what happened in the Himalayas is not an exception. Such tectonic events may explain all the major glaciation events in Earth’s history, including the ones that occurred before the Phanerozoic eon.
What Macdonald and his team did not comment on is how every glaciation event in Earth’s history played a crucial role in preparing Earth for human beings’ arrival. We humans enjoy the present surface temperature and atmospheric composition that we do thanks to these glaciation events. If it were not for each glaciation event occurring at the time that it did, lasting as long as it did, being as extensive as it was, and coexisting with the life that it did, humans would never have been able to exist on Earth. All that precise fine-tuning for each and every glaciation event shouts that nothing less than a super-intelligent, supernatural Being must be the Cause.
Featured image: Earth’s tectonic plates today
Image credit: United States Geological Survey