The Evolution of Earth: 35 Remarkable Facts From Its Past

Life most likely emerged on Earth almost instantaneously after becoming habitable. The first oceans formed 4.4 billion years ago, whereas current evidence supports the first life to have formed 4.28 billion years ago. Instantaneous of course means on a geological timescale here.

The earliest known life-forms on Earth are fossilized micro-organisms, found in hydrothermal vent holes in the seafloor. These were most probably chemosynthetic bacteria. These bacteria use sulfur compounds, particularly hydrogen sulfide, a chemical highly toxic to most known organisms, to produce organic material. Scientists have also recently found that hydrothermal vents at the bottom of the ocean are hot enough to emit enough light (mostly in the infrared spectrum) to support photosynthetic bacteria.

The vast majority of the Earth's gold and other heavy metals are locked up in the earth's core. Evidence from tungsten isotope studies indicates that most gold in the crust is derived from gold in the mantle which resulted from a meteorite bombardment some 3.9 billion years ago.

Purple Earth hypothesis suggests that early life forms on Earth may have been able to generate metabolic energy from sunlight using a purple-pigmented molecule called retinal that possibly predates the evolution of chlorophyll and photosynthesis. As a consequence, early Earth’s landmass may have looked purple.

Recent studies have suggested that photosynthesis may have begun about 3.4 billion years ago. But before photosynthetic organisms developed, the earth might have not been a blue planet at all. The unoxidized iron in the ocean might have given it a dark green or even black color. Then as photosynthesis ramped up, it would have turned the oceans red as the iron oxidized and the earth became a blue planet as the dissolved iron oxide precipitated to the bottom.

As many as six supercontinents are thought to have formed and broken up prior to Pangaea. Roughly 400 million years pass between each repetition of the supercontinent cycle, which is currently causing the Pacific Ocean to shrink until yet another supercontinent will someday be formed. The oldest supercontinent on earth is Vaalbara which formed 2.7 to 3.6 billion years ago.

Around 2.5 billion years ago, the Oxygen Catastrophe occurred, where the first microbes producing oxygen using photosynthesis created so much free oxygen that it wiped out most organisms on the planet because they were used to living in minimal oxygenated conditions

Before the Great Oxygenation Event which saw a rise in oxygen levels around 2.4 billion years ago, the earth’s atmosphere is thought to have originally been methane-rich. This would have given the sky anywhere from a purple to an orange tint due to hydrocarbon haze.

There is a period during Earth’s evolution where activity stalled which scientists dubbed ‘the boring billion’. Beginning roughly 1.7 billion years ago, the Earth became a slimy, near-static world of algae and microbes.

Salts do enter and form in the ocean, but they also leave it. Ocean salinity has been stable for billions of years. The two major processes capable of removing significant amounts of salt from the ocean are the formation of evaporites (rocks that form when restricted, salty water evaporates) and the sequestration of brine as groundwater on the continents. It's actually been proposed that the early ocean was saltier than today (maybe up to twice as salty). Salt was removed from the oceans over geologic time as the Earth cooled and the continents grew, providing more space favorable for salt/evaporite deposition and the formation of saline groundwater. It's been argued that modern-day salinity wasn't reached until relatively recently, perhaps playing a role in the origin and radiation of animal life (known as the Cambrian Explosion).