A sparkle of life.
The first steps of Life’ history are truly ancient. Since five billions of years ago the Solar system began to take its current shape but only one of its planet had the right distance from the Sun and the conditions to host Life: the Earth. The oldest traces of life that we know of are about four billion years old. However, only 2,5 billion years ago emerged the first unicellular organisms and then the first simple cellular colonies.
Hard to find, rare, and precious: meteorites land on our planet after a trip that started 4,6 billion years ago. Meteorites formed under the same conditions as the early Solar System, thus their composition is a snapshot of those ancestral chemical conditions.
At the beginning, Earth, Mars, and Venus had similar atmospheres: mainly a mixture of nitrogen, carbon dioxide and water vapor. Only on Earth oceans formed, removing much of the carbon dioxide from the atmosphere, something that did not happen on much warmer Venus and much colder Mars.
In 1952, Miller and Urey tested in their laboratory whether life could have risen from a mixture of inorganic compounds, in the presence of energy. They created an “inorganic soup” with electrical sparks passing through it. Extraordinarily the building blocks of proteins formed: aminoacids.
All single- or multicellular organisms whose cells have an enclosed nucleus and specialized organelles are called Eukaryotes, from amoebas to elephants. Their complexity probably originated from the symbiosis of Prokaryota, like Bacteria, single-celled organisms lacking the nucleus and cellular arrangements.
The first complex organisms lived only in the oceans. Some were so weird that we’re not sure if they were animals, or plants. Others, despite what they looked like, are some of our oldest ancestors. Only after millions of years of underwater evolution, plants and animals find their way out on the dry land. Suddenly, 280 millions of years ago, Life on Earth faced the most terrible mass exctinction ever, and 90% of the species disappeared.
Everything we know about our earliest origins comes from Pikaia, whose proto-notochord was the first step to the vertebral column. It lived 500 million years ago and it was the oldest ancestor of the evolutionary lineage of Vertebrates.
The great change (2013)MUSE - The Science Museum
Dunkleosteus was one of the first fishes with jaws, made of small, sharp, toothlike bony plates. The evolution of jaws allowed the first Vertebrates to feed on a wider variety of food, and thus promoted their great diversification.
Dry land: a tempting destination for evolution. For a vertebrate to leave their first prints, all it took was to slightly turn its fins... into legs. I took about three billion years to that fundamental alteration that would get on land the first tetrapod amphibians, as Ichthyostega.
Its jaws armed with long, curved canines would give no prey a chance. Meet Inostrancevia, a fearsome carnivorous reptile over 2 meters long. The upper Permian was the time of a group of reptiles called gorgonopsids.
After the Permian extinction the world belonged to the reptiles. Among them, a particularly successful group ruled the dry land for 150 million of years: the dinosaurs. Yet, new climate and ecological changes were shaping the Earth and the impact of a huge meteorite gave them the deathblow. Only few dinosaurs survived and their descendents, the birds, are still among us. Without dinosaurs, the ecological niches were left available to others. The evolutive radiation of Mammals was about to start.
Desmatosuchus, a relative of today’s crocodiles, was by nature a meek, ungainly herbivore that fed on tubers and roots. But be sure that very few would have dared attacking this indomitable Triassic archosaur. A sturdy armor of thorny bony plates covered its entire body.
Prosauropods mission: reach the vegetation meters high above the ground. Equipment: long necks, hind legs, and tails. Meet Plateosaurus, 7 meters worth of herbivorous dinosaur who teared leaves and twigs with its teeth and then shredded in its stomach, by ingesting small stones (gastroliths).
This little guy, called “Ciro” (Scipionyx samniticus), is one of the best preserved dinosaurs ever discovered. While most of the time paleontologists only find bones fragments, Ciro was mostly intact, with well preserved internal organs and even the remains of its last meal.
If you ever walk on the sandy hills of Montana or Dakota you may stumble across the fossil remains of Triceratops, one of the last dinosaurs (except for birds). A 9 meters behemoth which lived in the Northern American plains 70 million years ago.
During the Mesozoic reptiles occupied all the available ecological niches on the dry land, but they returned to the oceans as well, adapting to live underwater. The abundance of fossils of Notosaurs, Plesiosaurs and Ichtyosaurs from all over the world is here to prove it. Nonetheless, the dramatic events which wiped out the dinosaurs on the dry land didn’t spare them and about 65 millions of years ago most of them vanished away.
Nothosaurus lived in the seas during the Triassic, probably having a lifestyle like that of modern seals. It was adapted to swim, and its thick teeth were perfect to catch fishes, but it probably spent much time ashore as well.
Plesiosaurus was a marine reptile of the early Jurassic. Its limbs were completely transformed into powerful paddles while the tail was short and useless to swim. With its long neck and a mouth filled with curved teeth it was a fearsome threat for any fish around.
Ophtalmosaurus was one of the many species of Ichthyosaurs which lived during the Mesozoic. As its relatives, its hydrodynamic shape was similar to that of fishes and dolphins. Its peculiarity was a pair of enormous eyes, bolstered by bony discs.
Elongated body, large fins and sharp teeth: here is Mosasaurus. Despite its similarity with nothosaurs, plesiosaurs and ichthyosaurs, all related to each other, Mosasaurus evolved its hydrodynamic shape independently, being more closely related to snakes and lizards than to all the other marine reptiles.
After the dinosaurs disappeared, Mammals began a radiation in a wide spectrum of adaptations, promoted by their hallmarks: the hairs, the endothermy (the physiological regulation of body temperature) and above all, their advanced reproductive strategies, which include deep and long-lasting parental cares. Today, Mammals range from tiny shrews to massive blue whales, and live in every corner of the planet.
They look like furry ducks but there’s no joke, they are true and live in Australia. They even lay eggs in nests like ducks, and that’s not a joke too. Platypuses are among the last survivors of the Monotremes, an ancient group of egg-laying mammals.
Wallabies (Macropus rufogriseus), like all Marsupials, are born completely immature. And yet they climb their mother's body all the way to the pouch. Here they find nipples to feed on and they can complete their development in a warm and protected portable incubator.
In placental Mammals, mum’s love begins at conception. Throughout gestation, a crucial nutrient exchange connects mother and child through the placenta. After birth, the mother (and sometimes both parents) ensure the survival of her newborns by feeding, protecting, and training them for adult life.
The evolutionary radiation of Mammals has been relatively quick, and in few million of years they evolved many shapes, any size and occupied any habitat all over the world, from the depth of the oceans to the skys. Today, more than 5.000 Mammal species inhabit the Earth
Many Mammals call the water “home”: otters, seals, dolphins…and whales. Here is a fin whale (Balaenoptera physalus), the second largest animal living today. Despite its enormous size, it feeds on tiny fishes and crustaceans…thousands at once indeed, thanks to its baleen, a specialized filtering system.
The sky has proved to be a favorable habitat, and more than 1.200 species of bats have evolved, making them one of the most successful Mammal groups. Some of them eat fruits, but many others catch insects thanks to their superpower: echolocation.
Rodents take their name from the Latin word for “gnawing”: they all have evergrowing sharp incisors to do that. And there’s so much to gnaw on the ground and underground that Rodents are the most successful Mammal group, with more than 2.000 living species.
Primates are a special group of Mammals evolved among the branches of trees. Most of them still are arboreal, some others live on the ground. They are agile, they usually have a well developed visual perception and comparatively big brains. They are not so numerous as other Mammal groups but they have a special member within their ranks: us.
Lemur catta is likely the most popular of all lemurs, " night ghosts" of Madagascar. Though their flashy, black-and-white tail might look like a convenient means for hanging from branches, they live mainly on the ground and use them for balancing but also for communication.
Today Homo sapiens is the last man on Earth. But many human species have risen up before us, colonized the planet and sometimes coexisted with us.
Homo sapiens (2013)MUSE - The Science Museum
Homo sapiens’ is just one of many tales on one of many branches of the great tree of Life.