Life on Earth will not last forever. Several near life extinction events have happened on Earth in the past. Here they are listed in the order in which they have occurred.

To put everything in context, the Earth is about 4.5 billion years old. Single celled living organisms first appeared between 3.5 and 4 billion years ago. Complex life composed of multicellular organisms first appeared as much as 1.6 billion years ago. Plants first colonized land 515 million years ago. The first member of the genus homo, to which modern humans belong, appeared about 2.8 million years ago.

Ordovician Extinction
About 445 million years ago on Earth, two pulses of climate change occurred over a 2.4 million year period. The first pulse happened when the continent Gondwana became glaciated, changing the Earth from a hothouse to an icehouse climate. Sea levels lowered because of glaciation, and many animals living in shallow warm seas lost their habitat. The second pulse occurred when the Earth warmed again and intense worldwide oxygen depletion and toxic sulfide production in the oceans killed many species. The causes are still debated. Loss of life is estimated to have been 85% of all species.

Devonian Extinction
About 359 million years ago, one or more supernova explosions directed enough radiation onto Earth to eliminate the ozone layer and cause prolonged exposure to ultraviolet radiation, causing an extinction event. This ended the Devonian period and ushering in the Carboniferous. The supernova are estimated to have been 65 million light-years away. A supernova within 25 million light-years of Earth can extinguish all life. Loss of life is estimated to have been 70% of all species.

Permian Extinction "The Great Dying"
About 252 million years ago, extensive volcanic activity in the Siberian Traps, lasting 60 thousand years, caused carbon dioxide level in the atmosphere to rise to 2,500 ppm, compared to the 2025 year level of 425ppm, and the 1900 year level of about 300ppm. This resulted in massive climate change with 80% of marine species dying due to ocean acidification. On land, 70% of terrestrial vertebrate species died. More insect species died during this period than at any other time in Earth's history. This was the end of the Permian period and the start of the Triassic. Loss of life is estimated at 80% of all species.

Triassic-Jurassic Extinction
About 201 million years ago, a series of large scale volcanic eruptions happened over an 18 million year period. The increase in carbon dioxide levels to at least 1300ppm in the atmosphere caused gradual, but extensive, climate change and altered ocean acidity levels. Loss of life is estimated at 50% of all species.