Section 1.1: The Earth of the Archean Eon

What was Earth like during this time?

Currently, we remain in the Archean Eon, and the planet is vastly different from the world we know today. It resembles a water world, with oceans covering almost every inch of the surface.

However, these waters are not like those we experience now; they are acidic and lack oxygen. Beneath the waves, the Earth's crust is still forming, comprising not only oceanic crust but also continental crust. This continental crust, primarily made of granite, is pushed up from the mantle.

In terms of size, it accounts for only about 20% of today’s continental crust and is mostly submerged, but it signifies a beginning.

It’s plausible that by this time, some of the earliest micro-continents may have emerged above the ocean’s surface. One such landmass, known as Ur, could include parts of contemporary South Africa, Madagascar, India, Antarctica, and Western Australia. Yet, if Ur exists, it’s merely barren rock devoid of life.

Volcanic islands, reminiscent of those in modern Indonesia, do exist. However, these volcanoes are far more active than today's, releasing noxious gases into the Archean atmosphere.

Section 1.2: The Atmospheric Conditions

Consequently, the atmosphere of this era is drastically different from what we breathe today; oxygen is nearly absent, existing at less than 0.001% of today’s levels. Instead, the air is thick with greenhouse gases such as carbon dioxide, nitrous oxide, and water vapor.

This may seem alarming, yet it proves beneficial, as the Sun's luminosity is only 75–80% of what it is today. Without these greenhouse gases, Earth would likely face a deep freeze. Fortunately, the global temperatures remain warm, ranging between 50 to 85 degrees Celsius.

At this time, the Moon is approximately 15% closer to Earth than it is now, leading to shorter days of just 23 hours. Asteroid collisions are still frequent, with an estimated impact from a 10km-wide asteroid every 15 million years—similar to the one that contributed to the extinction of the dinosaurs.

Despite these harsh conditions, life has emerged. At the ocean's edge, microbial ecosystems are developing, with bacteria forming colonies that create distinctive structures known as stromatolites (which we will revisit).

Although the magnetic field offers some protection against relentless cosmic rays, the environment remains unforgiving. A stroll along the Ur shoreline would prove fatal within mere seconds.