How did life on earth evolve?

Answer 1

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.

Answer 2

Abiogenesis: Possibly a wall of lipids formed (a delimitation like today's membrane) spontaneously, trapping a nucleic acid (RNA according to the RNA world hypothesis) within. Once replication began and life began to reproduce, evolution could begin. Errors in nucleic acid replication would result in mutation. Those mutations that gave reproductive or nutrition-finding fitness or both reproductive and nutrition-finding fitness together survived and perpetuated and those that were not given this 'edge' did not.

Past abiogenesis, evolution truly begins, by Natural Selection. Throughout the Precambrian, single celled organisms evolved into multicelled and eukaryotic organisms. Photosynthesis evolved, first with molecules like H2S and then with molecules such as H2O, making sugars for nutrition.

Abiogenesis (spontaneous generation and not a panspermic viewpoint) occurred in the sea. From there there has always been a 'direction' of organisms from sea and water to land. Plants had to evolve air resistant and desiccation resistant spores and, if larger than mosses, would have to have support-giving tissue such as lignin, tracheids and xylem which also serves the function of channelling water against gravity from root or rhizoid to photosynthetic canopy leaf.

Sarcopterygian fish had to evolve lungs to breathe in air, and legs to support themselves (this was perhaps not essential as one considers the success of seals and mudskippers today, BUT TO MOVE ONTO LAND COMPLETELY they would have to develop supporting limbs. Lungs and limbs meant the transition from fish to amphibians. Laying eggs on land would require the development of a shell to prevent desiccation. The shell would also have to be porous to allow oxygen in and carbon dioxide out. Shelled eggs first evolved in reptiles.

But there is actually not a direction in evolution. Since life first popped into existence in the oceans and some life now lives on land, there appears to be a direction (from water to land). But there is no real direction. At the base of evolution is DNA and this inanimate, unconscious molecule just replicates itself within the constraints of its own evolution and its chemical nature and has no idea of what phenotype it actually codes for. Some DNA genomes survive and some do not as a result of the phenotype coded for that is the interactor with the physical and chemical environment.

Evolution has no direction. It simply happens as Natural Selection 'selects' reproductively successful population and eliminates others. Evolution from water to land seems to go backwards. Seals and cetaceans are an example. Seals are Carnivora that has returned to the sea and cetaceans are artiodactyls that have done so.

The 'direction' from crawling shrew to flying bat seems to go backwards in New Zealand where there is a species of bat that crawls on the forest floor to catch prey and does not catch meals on the wing.

Speciation is the production of new species. Populations may separate (perhaps geographically) and, both being reproductively successful, should diverge genetically until there is a point when the two populations can no longer interbreed. The populations would have speciated. Geographic separation gives allopatric speciation. Another type may be sympatric in which populations speciate within themselves with no geographic separation. Here, chromosomal fusions or fissions may occur or other meiotic anomalies which isolate parts of the population from breeding with the rest and being able to produce offspring. The chromosomal anomaly may become the normal. In any event, for sympatric speciation to occur, reproductive isolation must occur. Another way would be for the gametes to be incompatible between different groups.

Answer 3

The evolution of the planet's geology and the evolution of life itself were key factors in how life evolved over geological time.

Answer 4

god created life