In the long geological history of the Earth, humans first appeared during the Pleistocene Epoch, which dates back 1.6 million years to 10,000 years ago. Humans in modern form arrived during the Pleistocene Epoch, althoug... More »

Evidence suggests that the subspecies Homo sapiens sapiens, as anatomically modern humans are known, first emerged approximately 200,000 years ago. The Omo remains and fossils, from Omo National Park in Ethiopia discover... More » History Ancient History

There is evidence to suggest that archaic humans, of which modern humans are descended, were present as long as 195,000 years ago in what is now Ethiopia, as fossils recovered from the region show the beginnings of skull... More »

As of 2014, according to the U.S. Geological Survey, the best estimate of the age of the Earth is 4.54 billion years, based largely on the apparent age of meteorites that were presumably formed at the same time. The olde... More » Science Earth Science Geology

The first tree emerged during the Earth's Devonian period, which was approximately 416 million to 358 million years ago. Scientists believe the first tree was the Archeopteris, a species that is now extinct. More »

The first frogs appeared about 245 million years ago during the Triassic period. Since this time, frogs have remained relatively unchanged. They are amazingly adaptable and live in a variety of climates. More »

The geologic era in which humans have evolved and spread over the Earth is the Cenozoic Era. This time period began roughly 65 million years before the start of the 21st century. More »