In the last part of my philosophy series, “Thinking about the ‘Metaphysics’ in Metaphysical Naturalism,” I discussed cosmology and the origins of our universe from a naturalist and atheistic perspective. In this next part of the series I will be focusing more particularly on the origin of life in our universe (at least on the only planet currently known to host life, i.e. Earth), and the evolution of lifeforms from simple states to the intelligent minds of human beings today. This journey will require discussing: 1) the abiogenesis of life from non-living matter, 2) the evolution of biological diversity from common descent, 3) and the mind-body physicalism of human minds in a naturalist universe.
The planet Earth has been around for about 4.6 billion years, when a cloud of interstellar gas — filled with particles of ice, dust, rock, and other particles — collapsed to a point of concentrated mass, causing rising heat and the formation of our Sun. Most of the matter in this collapsing nebula fell into our Sun, but other material formed into a planetary disc in orbit around the Sun, causing particles to collide and eventually planets to take shape from cumulative bombardments with solid objects. The third planet from our Sun, Earth, happened to be in the Habitable Zone, which is the region in a solar system where a planet is neither too close nor too far from its star to form liquid water. Earth eventually formed liquid oceans on its surface and also an atmosphere with just the right greenhouse balance for the planet to be neither too hot nor too cold for complex life. The first surviving fossils of life date to about 3.5 billion years ago (about a billion years into our planet’s history) and scientists estimate that life on Earth could have began anywhere from 3.9-3.5 billion years ago.
This sequence of events has left us with a vexing question: what started life on Earth so long ago and how did it get to the point of us humans beings here today?