(answer from GPT-4)
If humanity were to disappear today, the transformation of Manhattan over three thousand years would be dramatic. The process of nature reclaiming the land would be both fascinating and complex. Here’s a speculative look at what might occur:
Immediate to Short-Term Changes (1-100 years):
- Power Outages: Without humans to maintain systems, electricity would fail almost immediately due to fuel depletion at power plants. This would lead to the cessation of pumps that currently keep the subway system and other low-lying areas dry.
- Water Infiltration: The absence of active maintenance and pumping systems would result in water flooding the subway tunnels within days or weeks. Buildings and infrastructure would begin to suffer water damage, especially in their foundations.
- Plant and Animal Colonization: Very quickly, plants would start to sprout in less dense areas such as parks, abandoned lots, and any crevices where soil and seeds could accumulate. Animals, including birds, rodents, and perhaps larger mammals migrating from less urban areas, would take over the city, making their homes in abandoned buildings and other structures.
Medium to Long-Term Changes (100-1,000 years):
- Building Deterioration: Without maintenance, buildings would begin to deteriorate quickly. Steel structures would rust due to exposure to water and air, while concrete would be weakened by freeze-thaw cycles and plant roots. Skyscrapers would eventually start to collapse due to structural failures.
- Tree Growth and Further Colonization: Trees and other vegetation would grow in and on buildings, their roots exacerbating the breakdown of materials. Over time, this would lead to more cracks and eventual structural collapses. Streets and avenues would likely be covered in soil and vegetation.
Long-Term Changes (1,000-3,000 years):
- Complete Reclamation by Nature: After a thousand years and beyond, most of Manhattan’s iconic skyscrapers would likely have collapsed due to the unchecked forces of nature. The combination of physical weathering, biological growth (like tree roots and microbial corrosion), and lack of maintenance would destroy rigid structures.
- Formation of New Ecosystems: The area would eventually transform into a new type of ecosystem, potentially a forested area if the climate supports it. This would be interspersed with remnants of human civilization such as stone, metal, and glass, which could take even longer to fully disintegrate or be buried.
Geographical Changes:
- Rising Sea Levels: Assuming ongoing climate change trends, rising sea levels might submerge lower parts of Manhattan, transforming the landscape into a series of small islands or marshlands. This could accelerate the destruction of human-made structures.
Conclusion: In three thousand years, without human intervention, Manhattan would be unrecognizable, transformed into a forest or a series of islands depending on sea levels, with the vast majority of its iconic architecture collapsed and overtaken by natural growth. The exact time it would take for all skyscrapers to be destroyed is hard to predict accurately but could range from hundreds to a thousand years, influenced by the materials used in their construction and environmental conditions.