It is not very likely that the total amount of water at Earth’s surface has changed significantly over geologic time. Based on the ages of meteorites, Earth is thought to be 4.6 billion years old. The oldest rocks known are 3.9 billion to 4.0 billion years old, and these rocks, though altered by post-depositional processes, show signs of having been deposited in an environment containing water. There is no direct evidence for water for the period between 4.6 billion and 3.9–4.0 billion years ago. Thus, ideas concerning the early history of the hydrosphere are closely linked to theories about the
What is Karman Line which tells the extent of Earth and beginning of space - Karman Line is named after Theodore von Kármán, a Hungarian-American physicist who in 1957 attempted to define boundary between Earth and outer space.
A substantial fraction of the freshwater needed to sustain natural and anthropogenic systems has its origin in mountain regions. Mountain areas are highly vulnerable to climate change, and anthropogenically caused changes to mountain hydrology are documented for most major mountain ranges. Yet, our current methods for observing mountain precipitation and its changes are extremely limited due to, high spatial heterogeneity of precipitation in complex topography, sampling biases from preferentially measuring precipitation in valleys, challenges in observing solid precipitation, the prohibitive cost in establishing and maintaining long term benchmarking sites, and severe measurement deficiencies in most remotely sensing products. These factors cause large uncertainties in precipitation estimates (spatial and temporal) over mountainous areas. In addition to precipitation, mountain hydrology is heavily influenced by snow redistribution and transfer across catchments, evapotranspiration, acc