Water on Earth!
The implication of the afore developments was that the planet, which started out as a ball of gases and elemental rocks, had stabilised to form a round, rocky body surrounded by gases and steam.
With the emergence of steam that accumulated above Earth’s surface gradually, water was set to be available in the form of rain(s). The volume of water that came down was too high, and it rained continuously for days and months! The rising levels of water filled two-thirds of the surface of Earth, spreading into its depressions, forming what we see as oceans today. With Earth taking its shape and water available in liquid form, life evolved.
Timescales
Now, let’s go through the past 500 million years of Earth’s history, out of which came humans as the result – the period of history that is most important to us. To understand the chronology of events that took and take place on Earth, we will put the concept of timescale in use. The different times of history are divided into eons, eras, periods and epochs for our convenient understanding.
The earliest eon in Earth’s history is named to be the Hadean Eon which began with the Earth’s formation, i.e., 4.6 billion years ago and lasted until 3.9 billion years ago. It was followed by Archeozoic eon from 3.9 to 2.5 billion years ago. And then came the Proterozoic eon, which extended from 2.5 billion years ago to 543 million years ago. From 543 million years ago till date, the Phanerozoic eon passes by.
The eons are further divided into eras, the eras into periods and the periods into epochs. Right now, we are living in the Holocene epoch of the Quaternary period in the Cenozoic era of the Phanerozoic Eon. (The names are a bit complex, yes).
Evolutions and Extinctions
After the evolution of multicellular organisms, life finally set foot on land around half a million years ago. Plants and animals of varying forms evolved on the planet’s surface with evolution continually taking place inside the oceans too! However, this period in the history of Earth saw an unexpected turn of events in the form of a mass extinction event!
Extinction, as we know, is the death of the population of a large number of species up to every last one of them due to some reason or the other. Apparently, this happens to be the first mass extinction event in the recorded history of the planet! With the topography of the planet undergoing constant change with time, it is nearly impossible to understand the cause of the event.
The first mass extinction event happened during the Ordovician period of the Phanerozoic eon. The periods that followed saw the rise and fall of various types of plants and animals, each living a contentious life before meeting their death in one extinction event or the other. It is recorded that Earth saw about 5 major extinction events (!) and several other minor extinction events till date.
Some scientists have propounded that Earth is currently going through the sixth mass extinction event, with the obvious reason being, us!
