SimEarth

In SimEarth, the player can vary a planet's atmosphere, temperature, landmasses, etc., then place various forms of life on the planet and watch them evolve. In the "Random Planet" game setting, the game is a software toy, without any required goals. The big (and difficult) challenge is to evolve sentient life and an advanced civilization, culminating in that species leaving the planet in an exodus. The development stages of the planet can be restored and repeated, until the planet "dies" ten billion years after its creation, the estimated time when the Sun will become a red giant and kill off all of the planet's life.

There are also eight scenarios that do have goals, the first three (Aquarium, Cambrian Earth, and 1990 Earth) involving managing the evolution and development of Earth in different stages, the next four (Mars, Venus, Ice Planet, and Dune) involving terraforming other planets to support life, and the final scenario (Earth 2XXX) involving rescuing life and civilization on a future Earth from self-replicating robots and nuclear warfare and giving the player the option of causing a great flood to help achieve this goal. In addition, there is another game mode besides Random Planet and Scenario mode, called Daisy World, where the only biome on the planet is daisies, which change their color relative to the temperature.

Will Wright was introduced to James Lovelock by Stewart Brand, a former editor of CoEvolution Quarterly who lived near Wright, upon hearing about SimEarth. Lovelock advised the development team behind SimEarth, and particularly assisted with geophysical models. Lovelock stated in regards to the Gaia model that "Attempts to model the Earth through simple sciences such as biology or biochemistry fail because the models are oversensitive to initial conditions and prone to chaotic disturbance." Gaia models link biology and geology however, which Lovelock claimed are "for some reason stable and able to resist perturbations." Lovelock expressed that SimEarth's simulation has "a degree of realism" despite it being "little more than a game", and he expressed that he had not seen or been involved in any computer simulations of nature on the scale of SimEarth at the time, noting that many professional climate models at the time did not take clouds, the ocean, or biology into account.

Computer Gaming World called SimEarth "absolutely fascinating". The reviewer wished that the game had more SimCity-like visual feedback, but stated that it was superior to its predecessor because of larger scope and greater replayability. It won the 1991 Software Publishers Association Excellence in Software Awards for Best Secondary Education Program and Best Simulation Program.

Entertainment Weekly gave the game an A− and wrote that "While it's never too early to teach kids to respect the biosphere, the same may not be true of introducing them to complicated simulations such as Simearth: The Living Planet (FCI, for Super NES), which has more variables (temperature, precipitation, etc.) than a polynomial equation. There's something to be said for this, though: A task as simple as 'growing a daisy'—one option offered here—requires knowing far more than which button to push to cream the bad guy."