Earth is estimated to be about 4.5 billion years old, and for much of that history it has been home to life in one weird form or another.
Indeed, some scientists think life appeared the moment our planet's environment was stable enough to support it.
The earliest evidence for life on Earth comes from fossilized mats of cyanobacteria called stromatolites in Australia that are about 3.4 billion years old. Ancient as their origins are, these bacteria (which are still around today) are already biologically complex - they have cell walls protecting their protein-producing DNA, so scientists think life must have begun much earlier, perhaps as early as 3.8 billion years ago.
But despite knowing approximately when life first appeared on Earth, scientists are still far from answering how it appeared.
"Many theories of the origin of life have been proposed, but since it's hard to prove or disprove them, no fully accepted theory exists," said Diana Northup, a cave biologist at the University of New Mexico.
The answer to this question would not only fill one of the largest gaps in scientists' understanding of nature, but also would have important implications for the likelihood of finding life elsewhere in the universe.
Lots of ideas
Data: The rise and fall of Earth's species
Today, there are several competing theories for how life arose on Earth. Some question whether life began on Earth at all, asserting instead that it came from a distant world or the heart of a fallen comet
or asteroid. Some even say life might have arisen here more than once.
"There may have been several origins," said David Deamer, a biochemist at the University of California, Santa Cruz. "We usually make 'origins' plural just to indicate that we don't necessarily claim there was just a single origin, but just an origin that didn't happen to get blasted by giant [asteroid] impacts."
Most scientists agree that life went through a period when RNA was the head-honcho molecule, guiding life through its nascent stages. According to this "RNA World" hypothesis, RNA was the crux molecule for primitive life and only took a backseat when DNA and proteins - which perform their jobs much more efficiently than RNA - developed.
"A lot of the most clever and most talented people in my field have accepted that the RNA World was not just possible, but probable," Deamer said.
To those who are looking for evidence of intelligent design, all the complex processes of life suggest design. However, they are explicable by evolution. Life has been evolving on the planet Earth for billions of years, which is long enough for complex processes to evolve.
To see if biological compounds could form spontaneously on early Earth To see if simple molecules can combine spontaneously. To find out how biological molecules could have first formed How life can evolve from nonliving matter
All life is the result of evolution.
In short... Nebula of gases --> Protostar --> Brown Dwarf --> Yellow Star --> Blue Giant --> Blue Super Giant --> Red Super Giant --> Super Nova --> Black Hole/Neutron Star/White Dwarf You should note that at any time in the life cycle of a star it may simply run out of fuel and then fade into a white dwarf. Interesting side-note if our sun should evolve into a blue giant it would eliminate all life on earth and if our sun were to run out of fuel and turn into a white dwarf it would eliminate all life on earth. Food for thought :)
Life?.. you know, birth to death etc..
Probably photosynthetic multicellular protists, such as Rhodophyta and Chlorophyta.
The first life apeared on earth some time around 4.4 billion years ago.
Life formed on earth because the conditions were right for life to begin and evolve. While some think that life (as we know it) is only possible on our earth, others think that somewhere, in the vastness of the Universe, life on a similar planet to earth must exist.
No, all life evolves. Bacteria evolve, viruses evolve, protists evolve, plants evolve, fungi evolve and animals evolve. Evolution is driven by Natural Selection. So, no. The evolution of all life on Earth is driven by Natural Selection: all bacteria, plants, animals, mammals, fish, insects, biochemical pathways, behaviours et cetera evolve by Natural Selection.
Life has shaped Earth through processes such as photosynthesis, which has transformed the atmosphere, while also influencing the climate and geography of the planet. At the same time, Earth's physical and chemical environment has provided the conditions necessary for life to evolve and thrive. Both life and Earth have had an interdependent relationship, each influencing the other in various ways.
It evolved in the oceans....there probably is a specific ocean or part of an ocean but that would be impossible to locate.
over time, life forms adapt to their new surroundings and become more complicated as the Earth changes.
Photosynthesis evolved multiple times in the history of life on Earth. It is believed to have evolved at least two separate times, leading to different types of photosynthetic organisms.
uhm, the earth?
Heavy bombardment is a critical event for life on Earth because it delivered water and organic compounds to the planet, which are essential for life to thrive. It also helped create the conditions for the development of a stable atmosphere and oceans. Without heavy bombardment, Earth may not have had the necessary ingredients for life to evolve.
Obviously, since both species are mammals.
mutation