You need to have a certain amount of elemental diversity to support the minimal requirements of living systems. For example, you need carbon, hence “carbon-based life”.
The Circumstellar Habitable Zone (CHZ)
Human bodies are made of carbon, and many other heavy elements. You need many different heavy elements in order to make up your physical body. Our star, the Sun, is also made of heavy elements. You also need heavy elements in order to crate a metal-rich star like our Sun. A heavy metal-rich star is required in order to support complex carbon-based life in any solar system. The metal-rich star is required because you need to make sure that it can burn stably for a LONG period of time. A metal-rich star also allows you to have a habitable planet far enough from that metal-rich star so that the planet can support liquid water on the planet’s surface. The zone where a planet can have liquid water at the surface is called the circumstellar habitable zone (CHZ). A solar system is therefore a lot like a campfire – you can’t get too close or you get set on fire, and you can’t get too far or you freeze to death. With planets, you need to keep away so your water doesn’t evaporate from the surface, but not so far away that your water freezes. Liquid water on the surface is needed in order to act as a universal solvent in the chemistry of life.
Here, watch a clip from The Privileged Planet: (Clip 4 of 12, full playlist here)
A metal-rich star like the Sun is very massive, which allows planets to stay in orbit much further away. Notice that the smaller the star, the closer you have to go to the star. If you go too close to the star then your planet is “tidally locked” – your planet no longer spins on it’s axis – and that’s very bad for life)
The Galactic Habitable Zone (GHZ)
So, where do you get the heavy elements you need for your heavy metal-rich star?
You have to get the heavy elements for your star from supernova explosions – explosions that occur when certain stars die. That’s where heavy elements come from. But you can’t be TOO CLOSE to the dying stars, because you will get hit by nasty radiation and explosions. So to get the heavy elements, your solar system needs to be in the galactic habitable zone (GHZ) – the zone where you can pickup the heavy elements you need but not get hit by radiation and explosions. The GHZ lies between the spiral arms of a spiral galaxy. You can be too close to the center of the galaxy, it’s too dense there and you will get hit with massive radiation that will break down your life chemistry. And you can’t be to far from the center, because you won’t get enough heavy elements from the lower number of dying stars in the spiral arms.
Here, watch a clip from The Privileged Planet: (Clip 10 of 12, full playlist here)
The GHZ is based on a discovery made by astronomer Guillermo Gonzalez, which made the front cover of Scientific American in 2001. That’s right, the cover of Scientific American. That’s when this was discovered.
By the way, you can watch a lecture with Guillermo Gonzalez explaining his ideas further. The lecture was delivered at UC Davis in 2007. That link has a link to the playlist of the lecture, a bio of the speaker, and a summary of all the topics he discussed in the lecture. An excellent place to learn the requirements for a suitable habitat for life. The GHZ and CHZ are ONLY TWO of the requirements for a habitat for life – there are a lot more requirements! Once you list them all out, the odds of getting even one place that is suitable are quite low. If you like this sort of evidence, I recommend the DVD of “The Privileged Planet”, which you can get on Amazon. Or just watch it for free on YouTube.
Positive arguments for Christian theism
- The kalam cosmological argument and the Big Bang theory
- The fine-tuning argument from cosmological constants and quantities
- The origin of life, part 1 of 2: the building blocks of life
- The origin of life, part 2 of 2: biological information
- The sudden origin of phyla in the Cambrian explosion
- Galactic habitable zones and circumstellar habitable zones
- Irreducible complexity in molecular machines
- The creative limits of natural selection and random mutation
- Angus Menuge’s ontological argument from reason
- Alvin Plantinga’s epistemological argument from reason
- William Lane Craig’s moral argument