The Origin of Life

Appearance of Homo sapiens

10 BCE

Homo sapiens, the first modern humans, evolved from their early hominid predecessors between 200,000 and 300,000 years ago. They developed a capacity for language about 50,000 years ago. The first modern humans began moving outside of Africa starting about 70,000-100,000 years ago. Furthermore, our earliest Homo ancestors most likely descended from Australopithecus afarensis, best known for the 3.2-million-year-old “Lucy” fossil found in Ethiopia’s Afar region.

Reign of the Dinosaurs

9 BCE

Dinosaurs lived between 230 and 65 million years ago, in a time known as the Mesozoic Era. New geologic discoveries suggest a climate catastrophe was the ticket for the dinosaur's rise to rule. At the time, about half the species on Earth died in the end-Triassic extinction. Scientists suggest massive volcanic eruptions could be to blame, spewing out lava and greenhouse gases that would have totally changed the climate, decreasing competition for food and enabling dinosaurs to take over.

Increased Biodiversity (Cambrian Explosion)

8 BCE

The Cambrian explosion or Cambrian radiation was an event approximately 541 million years ago in the Cambrian period when practically all major animal phyla started appearing in the fossil record. It lasted for about 13 – 25 million years and resulted in the divergence of most modern metazoan phyla. Furthermore, given the importance of oxygen for animals, researchers suspected that a sudden increase in the gas to near-modern levels in the ocean could have spurred the Cambrian explosion

Appearance of Multi-cellular Organisms

7 BCE

Single-celled organisms evolved into complex multicellular organisms about 600 million years ago. One hypothesis is that predation put selective pressure on single-celled organisms, causing them to become more complex. So to test the validity of this in a lab, scientists have put a single-celled filter-feeding predators in the mix, Paramecium tetraurelia and watched what happened. The researchers watched over 50 weeks, two out of five experimental populations evolved into multicellular life.

Appearance of Eukaryotes

6 BCE

The first eukaryotic cells - cells with a nucleus and internal membrane-bound organelles - probably evolved about 2 billion years ago. This is explained by the endosymbiotic theory. Endosymbiosis came about when large prokaryotic cells engulfed small cells. The small cells were not digested by the large cells. Instead, they lived within the large cells and evolved into organelles, producing the first eukaryotic cells.

Appearance of Photosynthetic Prokaryotes (Cyanobacteria)

5 BCE

Cyanobacteria formed between 2.7 and 2.45 billion years ago when the isotopic ratio of sulfur transformed, indicating that oxygen was becoming a significant part of Earth's atmosphere. Moreover, tiny organisms, cyanobacteria, began conducting photosynthesis: using sunshine, water and CO2 to produce carbohydrates and oxygen. Photosynthesis likely evolved multiple times and modern photosynthesis may have arisen from the fusion of two different photosynthetic systems via lateral gene transfer.

Appearance of Prokaryotes (Stromatolites)

4 BCE

Approximately 3.5 billion years ago. Stromatolite deposits are formed by sediment trapping and binding, and/or by precipitation activities of the microbial communities. Before cyanobacteria, the air was only 1% oxygen. Then, for 2 billion years, photosynthesising Stromatolites pumped oxygen into the oceans (like underwater trees, before trees existed). When the oceans’ waters were saturated, oxygen was released into the air, and with around 20% of oxygen in the air, life was able to flourish.

Formation of Crust and Oceans (about 3.8 billion years ago)

3 BCE

Other terrestrial planets, Mercury, Venus, and Mars, and even the Moon have crusts. Like Earth, these crusts are formed mostly by silicate minerals. Unlike Earth, however, the crusts of these celestial bodies are not shaped by the interaction of tectonic plates. For Earth, heavy metals, sank to the center of the new planet and became the core. Over millions of years, the molten core cooled and outgassing occured solidifying the mantle and releasing water vapor which rained down and became oceans

Formation of the Solar System

1 BCE

Our solar system formed about 4.5 billion years ago from a dense cloud of interstellar gas and dust. The cloud collapsed, possibly due to the shockwave of a nearby exploding star, called a supernova. When this dust cloud collapsed, it formed a solar nebula—a spinning, swirling disk of material.

Late Heavy Bombardment

1 BCE

-Thought to have occurred approximately 4.1 to 3.8 billion years ago. -Most researchers think the Late Heavy Bombardment was caused by giant planets moving around, orbiting closer to and farther from the sun and pushing lots of smaller solar system objects, like asteroids, along with them. The asteroids would have whizzed around the inner planets, crashing down in a rain of fire that left their surfaces scarred for billions of years. This period is known as the Late Heavy Bombardment.