Here's a breakdown of why:
* Scale: Earth is vast. A dome large enough to encompass even a small portion of the planet's surface would be incredibly challenging to construct and maintain.
* Atmosphere: Replicating Earth's atmosphere within a dome would require precise control of gas composition, pressure, and temperature. This is a major engineering hurdle, and maintaining the balance of various atmospheric gases would be nearly impossible over long periods.
* Hydrosphere: Creating and maintaining a functional water cycle within the dome, with evaporation, precipitation, and water flow, would be exceptionally difficult.
* Biosphere: Replicating Earth's diverse ecosystems, with all their interdependencies, would be a monumental task. It would involve maintaining biodiversity, food chains, and complex interactions between organisms.
* Geosphere: The dome would have to simulate geological processes like plate tectonics, volcanic activity, and mineral formation, which are deeply intertwined with Earth's other systems.
* Energy Sources: The dome would need a sustainable and powerful energy source to power all the systems and maintain a stable environment.
However, the concept of a "biosphere" is not entirely fictional:
* Biosphere 2: In the 1990s, a large-scale experiment called Biosphere 2 was built in Arizona. It aimed to create a self-sustaining closed ecosystem, but it faced many challenges and ultimately failed to achieve complete independence from the outside world.
* Smaller-scale experiments: There are ongoing efforts to create closed-loop systems, sometimes called "mini-biospheres," in smaller scales. These experiments are valuable for studying ecological interactions and potential applications for space travel, but they are still far from replicating Earth's complexity.
Ultimately, while the concept of a sealed glass dome with all the features of Earth is appealing, it is currently beyond our technological capabilities. However, scientific advancements and technological innovations could one day lead to more sophisticated closed ecosystems, offering valuable insights into the interconnectedness of life and the challenges of creating self-sustaining environments.