origin of life

Formation of the Earth Crust & Ocean

10 BCE

(4.5 billion years ago) Earth formed from the accretion of interstellar dust and debris. During accretion, the growing mass, called proto-Earth, was compressed by gravity, causing an increase in temperature. This rise in temperature, along with additional heat supplied by radioactive decay, caused the proto-Earth to become a hot molten mass. As the proto-Earth cooled, it stratified according to density leading to a layered composition.

Earliest Evidence of life

9 BCE

(3.8 billion years ago) consists of rock samples containing organic compounds with an isotopic signature low in carbon-13.

First Fossil Evidence

8 BCE

(3.5 billion years ago) Modern stromatolites are layered mounds composed of mineral sediments and organic compounds formed by successive generations of microbial communities. Geologists have found comparable mounds dating as far back as 3.4 billion years ago that appear to be formed by similar processes. These fossil stromatolites provide the oldest physical evidence for life on Earth

Evolution of Prokaryotic cells

7 BCE

(2.5 billion years ago) prokaryotic cells were likely a diverse group of single-celled organisms, primarily anaerobic (not requiring oxygen), with some early photosynthetic bacteria like cyanobacteria emerging, which would later significantly alter Earth's atmosphere by producing oxygen through photosynthesis, marking the "Great Oxidation Event."

Evolution of Eukaryotic cells

6 BCE

(2.4 billion – 2.0 billion years ago) A hallmark of eukaryotes is the presence of internal organelles, such as a nucleus and mitochondria, which are not found in prokaryotes. Genetic evidence has revealed that mitochondria in fact arose from a symbiotic relationship in which a bacterium was engulfed by another cell, perhaps an archaea. The origin of eukaryotes triggered a biological revolution, which set the stage for multicellularity and increased size and complexity.

Proliferation of Cyanobacteria

5 BCE

(2.0 billion years ago) Cyanobacteria are the only group of organisms known to have evolved the ability to produce oxygen from photosynthesis and so are thought to be responsible for the oxygenation of the atmosphere — a process that took several hundred million years.

Evolution of Multicellular organisms

4 BCE

(635 milllion years ago) The precursors of multicellular animals were likely single-celled protozoans. They evolved predatory feeding by ingestion, enabling rapid cycling of organic matter and higher energy production, which led to increased size and multicellular complexity. Animals begin to appear in the fossil record 635 million years ago, but genetic estimates suggest they evolved as early as 800 million years ago.

Cambrian Explosion

3 BCE

(525 million years ago) Trilobites are a large group of extinct arthropods that were numerous during the Cambrian explosion. They roamed the seas for approximately 250 million years before disappearing during the Permian-Triassic mass extinction

First Land Plants

2 BCE

(340 million years ago) During the Carboniferous Period (approximately 360 million to 300 million years ago), terrestrial plants increased in diversity, leading to more complex ecosystems. The vast amounts of organic matter buried during this period are the principal source of fossil fuels that humans use today.

Dinosaurs

1 BCE

(155 million years ago) Age of Dinosaurs
Dinosaurs first appeared during the Triassic Period about 230 million years ago and were the most prevalent large animals in the mid- to late Mesozoic Era (200 million to 66 million years ago). Over this time, they developed an incredible diversity of body shapes and sizes. They ranged in size from less than half a meter in length to over 23 meters. Some dinosaurs took to the air and their descendants became modern birds.