What was the Earth like when life was first born? A question that has intrigued science for centuries.
Today, most scientists insist that it arose from a simple chemical reaction, which chaotically transformed non-living matter into the first living cell.
Nevertheless, this explanation is insufficient in the absence of concrete evidence, even for its most ardent supporters.
Today, every corner of the Earth is teeming with life. From the poles to the equator, from deep caves to mountain ranges, from tropical forests to volcanoes, at least primitive organisms can be found everywhere.
Animals, plants, fungi and bacteria in search of living space have adapted to the harshest conditions. However, scientists believe that for most of its history, the Earth has resembled a rather inhospitable place.
When life first appeared on Earth, some 3.8 billion years ago, the planet looked very different from the one we know today. Back then, the Earth's surface was mostly water, with small archipelagos and undeveloped land masses.
The atmosphere was also very different from today's, with a high proportion of gases such as methane, ammonia and carbon dioxide.
These gases were produced by massive volcanic eruptions and chemical reactions in primitive oceans.
There was also very little oxygen in the atmosphere, as photosynthetic organisms capable of producing oxygen had not yet appeared.