-
Asked by jamjarjarvis to Barbara, Matt, Ravinder, Sophie, Tristan on 17 Mar 2015.
-
Matthew Moore answered on 17 Mar 2015:
Well the earth was formed about 4.5billion years ago and life on this planet started around 3.5billion years ago, once conditions were right and the planet had cooled sufficiently.
Humans didn’t then, at once, come into existence but were the product of 3.5billion years of evolution!
Hominids (the evolutionary group of which humans are part) split from apes a few million years ago, a few very human-like species evolved, mainly in Africa and finally Homo sapiens in Africa about 200,000 years ago. This means that all humans living today and all humans ever originated in Africa!
About 120,000 years ago humans first made the trip out of Africa while the North (the Sahara) was a lush forest (there’s geological evidence for this climate), generations moved into the Arabian Peninsular but then the climate changed and they didn’t make it any further. Their fossils have since been found and they appeared to have very early cultural behaviours such as burying the dead with a ceremony.
Then about 80,000 years ago, humans successfully made it out of Africa. They travelled along the Arabian peninsular, the south of India and south through Indonesia and even making the crossing to Australia. Further from here, human tribes made it to far flung polynesian islands in the pacific ocean.
At the same time humans travelled north from the Arabian peninsular into what would now be Crimea, Ukraine. From here they travelled West through Europe. Other tribes of humans, generations even (this happened over tens of thousands of years) travelled east to China and North East to Siberia and Russia. From here a great ice plate connected the East coast of Russia and the West coast of America. Humans made this crossing and to America about 15,000 years ago.
This is why when early explorers of modern civilisation made it to America and to Australia that there was already people living there, they had been living there for tens of thousands of years!
-
-
Sophie Robinson answered on 19 Mar 2015:
This is a very philosophical question indeed! If you push religion to the side and instead only our understanding of the physical development of life we can get closer to an achievable answer. We know, thanks to Hubble’s law, that universe is about 14.5 billion years old. The Earth has existed for the last 4.5 billion years of this period. We know this thanks to the radioactive decay which can be measured from the rocks on the Earth.
Human life is the result of a huge range of chance encounters throughout the history of the Earth. Primordial life is believed to have started in the warm geo-active pools which formed a couple billion years into the Earth’s evolution. Liquid water is key to life on earth. It is believed that a Mars-sized planet (called Theia) collided with the Earth in its early life, creating the moon and bringing water with it. Comets have also helped to add liquid water to the Earth.
Life starts as simple chemical elements which evolve into simple molecules through exposure to heat, ultra-violet light and a lot of luck. Eventually, these simple building blocks develop in proteins and amino acids which are important for developing DNA. Green-blue algae was the first photosynthesising organism on the planet, and was key in converting the huge amounts of carbon dioxide from volcanoes into oxygen. This helped to cool the planet and get the climate just right for larger animals.
The dinosaurs eventually evolve (225 million years ago). Two huge asteroids wipe out about ninety percent of all life about 90 million years ago. This allowed mammals to evolve (eventually) into humans (homo-sapiens).
Comments