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www.reference.com/article/old-life-earth-7c73ff08dc120721

The earliest fossil evidence found suggests that life has existed on Earth for 3.5 to 3.9 billion years. The surface of the planet was hypothesized to be inhospitable to all life until after the Late Heavy Bombardment, which occurred roughly 3.8 to 4.1 billion years ago...

www.reference.com/article/life-earth-end-d2692340d8af0418

According to astrobiologist Jack O'Malley-James of the University of St. Andrews in Scotland, the sun will grow large enough to extinguish all life on Earth in roughly 2.8 billion years. The planet's non-microbial life will become extinct in 800 million to 1.3 billion y...

www.reference.com/article/did-life-begin-earth-1296312b63a46ebb

While there are many theories as to how life began on Earth, no theory has been accepted as truth, according to NBC News. Biologist Diana Northup from the University of New Mexico says this is because it's hard to prove or disprove many of these theories.

www.reference.com/article/earth-support-life-5fd50bdfdc547b7

Earth supports life because it is the correct distance from the sun, its composition is rock, it has a molten core, it gains protection from its atmosphere and it has water. There are approximately 500 planets in the Milky Way capable of supporting life.

www.reference.com/article/first-human-earth-e7381b90ff1d923d

While there is no way to determine a precise point at which the human species became distinct from their proto-simian ancestors, the earliest known human ancestor has been identified as Ardipithecus ramidus, or Ardi for short. Ardi, a female of her species, lived approx...

www.reference.com/article/first-animal-earth-9d4f4108a11d28f5

As of 2015, scientists believe the first animal on Earth was the comb jelly of the phylum Ctenophora. It is an ocean-dwelling, gelatinous organism whose length varies from less than half an inch to 16 inches. Until 2008, sponges of the phylum Porifera were considered th...

www.reference.com/article/life-exist-earth-8baf773d35507bfb

Life exists on Earth because of many different factors. Scientists have varying opinions, but do agree on a few key important requirements necessary for life to exist on Earth, such as the presence of water and the fact that Earth occupies a habitable zone around the su...