The statement that oceanic crust cannot be older than 200 million years is based on the process of plate tectonics and the concept of seafloor spreading. Oceanic crust is continuously being created at mid-ocean ridges through volcanic activity, where magma rises to the surface, cools, and solidifies, forming new crust. As this process occurs, older crust is pushed away from the ridge and eventually subducted beneath continental plates or other oceanic crust in subduction zones.

Since the theory of plate tectonics suggests that the oldest oceanic crust is typically no more than around 200 million years old, this implies that older oceanic crust has been recycled back into the Earth’s mantle through subduction. This process effectively renews the oceanic crust, preventing it from accumulating to ages much older than 200 million years.

However, it’s important to note that there are exceptions to this general rule. Some fragments of ancient oceanic crust, known as ophiolites, can be found in certain geological settings, such as mountain belts, where they have been preserved and uplifted through tectonic processes. These ophiolites provide valuable insights into the history and evolution of oceanic crust, but they are relatively rare compared to the ongoing formation and recycling of younger oceanic crust at mid-ocean ridges and subduction zones.

Determining if a building is earthquake safe just by looking at it from the outside is quite challenging. A building’s seismic safety depends on various factors such as its design, construction materials, foundation, and adherence to building codes and standards.

Some general visual indicators of seismic safety might include the presence of diagonal bracing, shear walls, or other seismic retrofitting elements visible on the exterior. However, a thorough assessment of a building’s earthquake safety typically requires an inspection by a qualified structural engineer or a seismic safety expert. They can evaluate the building’s structural integrity, foundation, and overall seismic resistance through a detailed inspection and analysis.

No, geology and geography are not the same thing. They are related fields but have distinct focuses:

1. Geology: Geology is the study of the Earth’s physical structure, composition, and processes. Geologists examine rocks, minerals, fossils, and the Earth’s interior to understand its history and the forces that shape it, such as plate tectonics, earthquakes, and volcanoes.

2. Geography: Geography is a broader field that encompasses the study of the Earth’s surface, its features, and the relationships between people and their environments. It includes aspects like human geography (population, culture, urban planning) and physical geography (landforms, climate, ecosystems), among others.

In summary, while both geology and geography involve the study of the Earth, geology focuses on its physical properties and processes, while geography has a broader scope that includes the study of both the physical and human aspects of the Earth.