AP BIOLOGY

Detailed explanation-1: -The oldest fossils on Earth show that 3.5 billion years ago there was life on our planet.

Detailed explanation-2: -Evidence of microbes was also preserved in the hard structures (“stromatolites”) they made, which date to 3.5 billion years ago. Stromatolites are created as sticky mats of microbes trap and bind sediments into layers. Minerals precipitate inside the layers, creating durable structures even as the microbes die off.

Detailed explanation-3: -However, a recent study suggests that, despite the contribution of these possible impacts, much of the Earth’s water may have actually formed from the hydrogen and oxygen present in very building blocks of the planet itself. Thus, about 4.4 billion years ago we had a nearly habitable Earth, covered by a global ocean.

Detailed explanation-4: -Earth and its atmosphere are continuously altered. Plate tectonics shift the continents, raise mountains and move the ocean floor while processes not fully understood alter the climate. Such constant change has characterized Earth since its beginning some 4.5 billion years ago.