When do you believe life on earth originated?

Answer 1

The most widely endorsed view of the origin of life is that processes on Earth assembled inorganic molecules into larger organic molecules and ultimately into self replicating entities. This area of investigation is called Abiogenesis. (See related links.)

There are quite a number of alternative explanations, including the explanation that life was transported to Earth from some extraterrestrial source. The extraterrestrial view omits the need to explain how life started somewhere else. One can list approximately a dozen major theories with some scientific basis and the interested reader will find extensive resources that explain these. No one explanation is considered true or even highly likely. The scientific process of inquiry continues.

There are also nonscientific explanations of the origin of life, Earth, the Universe and all of evolution. The interested reader will find extensive resources that explain these. They may wish to start with the religious teachings of their own culture.

Answer 2

The current consensus is that life has existed on Earth for some 3.5 billion years. This consensus formed on the basis of geological evidence, of microfossils, and of dating via the "molecular clock", which uses current diversity and estimates of divergence rates to extrapolate a time for a hypothetical common origin.

Answer 3

All we have is a big window when it happened - and no way to prove one way or another how it happened. Let's look.

The earth formed a long, long time ago. Billions of years. We have bulletproof radiometric evidence that almost no one who understands radiometric dating disputes that the earth is about 4.54 billion years old. Life appeared somewhere between 4.4 billion years ago and 2.7 billion years ago. We just don't have any data to pin it down more than that. But what do we know?

The earliest forms of life we know of are still with us today - blue-green algae. In a place called Shark Bay in southwest Australia, the formations these microorganisms create can be see alive and well and covered in the thin film of algae that created them of a long, long time. And inland from there and dating bact billions of years can be seen fossilized versions of these same structures - stomatolites. The earliest one we've been able to date goes back 2,724 million years. That's 2.724 billion years. What is the hot topic for debate? Glad you asked.

When we study the fossils, we have indications that they were created through biological activity - which is what one might expect. But further study also suggests that abiotic (non-organic) precipitation may have had a hand in things. The debate continues. Life had to come from somewhere. But where?

As the question asks "when do you believe..." as posted, there is plenty of room for The Bible thumpers to come along and put up what they like. Certainly if I ignore them and believe what science tells me (and science does not say how life on earth began, by the way), I won't have a problem. God will not condemn me for using what is arguably the finest gift one could get from any creator to discover the nature of the earth and how it evolved over the billions of years we know have elapsed since it was formed. Got links if you can handle the science and are curious. They're to articles posted by Wikipedia - where they are not afraid of truth, either.

Answer 4

About 3.5 billion years ago is what I heard :)
3.5 billion years ago is the oldest direct evidence for life on Earth. Direct evidence is found in 3.5-billion-year-old cherts (rocks deposited in the ocean) in which several microorganisms have been identified. These microogranisms are much like cyanobacteria which is found in abundance throughout the Earth today.

3.8 billion years ago is the oldest indirect evidence for life on Earth. Indirect evidence is found in 3.8-billion-year-old banded iron deposits (chert) which contain a Carbon 13 to Carbon 14 ratios similar to ratios found in organisms today.