Terran Planet

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A Terran Planet is a planet template that mimics Earth. Terran Planets will follow Earth's history in how they are first formed, the first few geological events they face, and how life evolves on them. It is the template we will use to initially generate planets and design our game, until we have enough content in the game and enough knowledge on the team to start simulating more exotic and alien planet templates.

Overview

Terran Planets always share the following characteristics:

• Planet Composition: The planet is formed with a nitrogenous atmosphere, and mostly solid and molten silicate rocks, and an iron/nickel based core which creates a magnetic field around the planet.
• One Moon: The planet forms an orbiting moon early in its history
• Liquid Water Oceans: Liquid water oceans form early in the history of the planet, as the planet cools and as the densifying atmosphere condenses the water vapour to precipitate into rain
• Creation of Biomolecules: Lightning and radiation constantly generate and destroy biomolecules (glucose, ammonia, phosphate) near the ocean surface, but water currents carry some of these to the deep ocean where they accumulate. By the time life develops, there will be large reserves of these biomolecules accumulated.
• Origin of Life: Life first develops near Hydrothermal Vents, facilitated by their heat and the accumulation of biomolecules around them.
• Chemistry of Life: Life evolves to be carbon-based, using Glucose, Ammonia, and Phosphate to grow and reproduce
• Evolution of Niches: Life quickly proliferates and starts consuming the biomolecules faster than natural processes can replace them. Eventually, the surplus biomolecules in the environment will run out, and there will be life's first extinction event on this planet. Species that adapted new reliable ways to acquire energy will survive, and the rest will die out.
• Oxygen: Life eventually evolves Oxygenic Photosynthesis, a biological process that begins to produce oxygen in the planet.
• Great Oxygenation Event: The accumulation of oxygen eventually leads to a Great Oxygenation Event (GOE), where much of the chemical composition of the planet is radically changed by the introduction of oxygen. Oxygen is a highly reactive element that reacts with many of the formerly present chemicals to produce new substances. There is also a massive extinction as many species die from oxygen toxicity. The remaining species adapt to use oxygen, or retreat to anoxic environments (deep oceans and caves).
• Ozone: The release of oxygen into the atmosphere leads to the creation of an ozone layer. The ozone drastically reduces radiation levels on the surface, making it more tolerable for life to survive. However, it also reduces the natural production of glucose, ammonia, and phosphate from radiation hitting surface water.
• Snowball Planet: The onset of a GOE event leads to a Snowball Planet event later on. This is because the oxygen reacts with the methane in the air to produce carbon dioxide and water. This leads to a largely methane filled atmosphere being replaced with a largely carbon dioxide and oxygen filled atmosphere. Methane is a much stronger greenhouse gas than oxygen and carbon dioxide, and so a rapid cooling of the planet begins. This Snowball Planet event acts as another extinction event, killing all of the species that do not adapt in time.
• From the end of the Snowball Planet event onwards, the rest of the planet's history is essentially random.
• To be filled out with the rest of the characteristics...

The following is a timeline of major natural events that are likely or guaranteed to occur on Terran planets.

Hadean Eon

The Hadeon Eon is the first geological eon in a Terran planet's history. It begins with the original genesis of the planet, and ends with the origin of life. It is an unplayable eon of your planet's history, and will simply be used to generate your planet's starting conditions.

It is a hellish period of a Terran Planet's history, characterized by extreme energy flows resulting in a scorching planet with a molten surface, intense volcanic activity, and regular asteroid showers.

Conditions

• Atmosphere
  • Compounds: Mostly CO2, some Hydrogen and Water Vapour. Oxygen at 0.01% .
  • Surface Temperature: 230 degrees Celsius.
  • Pressure: 27 atm.
• Hydrosphere
  • Oceanic Temperature: Around 50-85 degrees Celsius.

Atmosphere

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The atmosphere at this time would be largely comprised of carbon dioxide, water vapour, methane, and sulfate (Need a reference for sulfate). As time goes by and the planet cools, the subduction of tectonic plates draws carbon dioxide out of the atmosphere and into the lithosphere. The oceans as well slowly dissolve carbon dioxide out of the atmosphere and into the hydrosphere. This gradually reduced the pressure and temperature of the atmosphere.

Hydrosphere

The starting planet would have a lot of water vapour, and the intense pressure of the early atmosphere would condense this water into the planet's first oceans despite the fact that surface temperatures exceed 200 degrees Celsius . The high concentration of carbon dioxide in the atmosphere means much of this carbon dioxide will also leech into the oceans, creating a lot of acidity .

Lithosphere

The planet starts extremely hot and full of energy. This is a result of the planetary accretion event, the formation of the metallic core, and the decay of radioactive elements trapped in during its initial accretion . Many parts of the planetary surface are molten at this time, but the formation of oceans rapidly cools some of these regions. Additionally, the planet itself is cooling as the energy of its initial formation dissipates. Lastly, the gradual decrease of carbon dioxide from the atmosphere (as it gets drawn into the lithosphere and hydrosphere) cools the surface temperature on the planet by reducing the greenhouse effect, helping the molten rocks solidify.

Volcanic activity is very high at this point.

Late Heavy Bombardment

As the solar system is still early in its history, there are still a lot of asteroids orbiting through the solar system on unstable trajectories, and many of these will collide with the planets of the solar system.

These impacts will generate a lot of energy which can produce biomolecules (glucose, ammonia, phosphate) on the planet. They can also lead to mini extinctions for the first colonies of life, and cause abrupt and short-lived climactic changes . These asteroids can also bring with them many compounds themselves, like water, minerals, or even biomolecules. These impacts would also draw a lot of oxygen out of the atmosphere , making it a rare gas early in the planet's history.

The frequency of these impacts appears to be about one asteroid with a diameter greater than 10km every 15 million years even into the Archean Eon , which is about the size of the asteroid that killed the dinosaurs.

The Late Heavy Bombardment will die down after 100-300 million years, lasting into the Archean Eon.

Moon Formation

Placeholder.

Archean Eon

The Archean Eon is the second geological eon in a Terran planet's history. It begins with the origin of life on the planet, and ends with the accumulation of oxygen in the atmosphere. It is the first playable eon of your planet's history, since you start as the first species of life.

Conditions

• Atmosphere
  • Compounds:
  • Surface Temperature:
  • Pressure: 10-100 atm
• Hydrosphere
  • Oceanic Temperature:

Geology

The majority of the planetary crust solidifies by this time. There are still some areas on the surface that are molten. The solidification of the crust leads to the formation of the planet's first tectonic plates, and thus the beginning of tectonic activity .

Snowball Planet

The accumulation of oxygen in the atmosphere from the GOE triggers a cascade of many effects. One of these is the depletion of much of the methane in the atmosphere. This is because oxygen reacts with methane in the atmosphere to form carbon dioxide and water. The reduction of methane reduces the greenhouse effect of the atmosphere, and leads to a rapid cooling of the planet . This is referred to as a Snowball Planet, because it is believed that much of the planet was covered in glaciers.

The first major glaciation event triggered by the GOE occurs around 500-600 million years after the evolution of oxygenic photosynthesis (the Pongola Glaciation on Earth).

The second major glaciation event occurs around 1.3 billion years after the evolution of oxygenic photosynthesis (the Huronian Glaciation on Earth).

Proterozoic Eon

The Proterozoic Eon is the third geological eon in a Terran planet's history. It begins with the accumulation of oxygen in the atmosphere, and ends with the origin of multicellular life. This is a less objectively demarcated eon, as it is (however slightly) possible for multicellular life to evolve before the accumulation of oxygen in the atmosphere.

Conditions

• Atmosphere
  • Compounds:
  • Surface Temperature:
  • Pressure:
• Hydrosphere
  • Oceanic Temperature:

Phanerozoic Eon

The Phanerozoic Eon is the fourth and final geological eon in a Terran planet's history. It begins with the origin of multicellular life, and ends with the death of the planet.

Conditions

• Atmosphere
  • Compounds:
  • Surface Temperature:
  • Pressure:
• Hydrosphere
  • Oceanic Temperature:

Further Reading

https://en.wikipedia.org/wiki/List_of_planet_types