unit H project

Formation of the Earth Crust and Ocean

4567 BCE

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

3800 BCE

The earliest evidence of life consists of rock samples containing organic compounds with an isotopic signature low in carbon-13.

evolution of prokarypotic cells

3600 BCE

prokaryotic cells are considered the first life forms on Earth, evolving from simple protocells and gradually diversifying into the domains Bacteria and Archaea

First fossil evidence

3500 BCE

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 Eukaryotic cells

2300 BCE

eukaryotic cells evolved from prokaryotic cells through a process called "endosymbiosis," where a larger prokaryotic cell engulfed smaller prokaryotic cells, which eventually became organelles like mitochondria and chloroplasts within the larger cell, leading to the complex structure of a eukaryote

evolution of multicellular organism

2300 BCE

The evolution of multicellular organisms is believed to have occurred when single-celled organisms began to stick together after cell division, eventually developing specialized functions and forming colonies that grew more complex over time, leading to the emergence of multicellular life forms with differentiated cell types and division of labor

Proliferation of Cyanobacteria

1598 BCE

Analogous to mitochondria, chloroplasts resulted from a symbiotic event in which a photosynthetic bacterium (likely a cyanobacterium) was engulfed by a host eukaryote. Over time, the engulfed organism evolved to become a specialized photosynthetic organelle

Caribian explosion

530 BCE

marks the most rapid evolution of new animal phyla and animal diversity in Earth's history. It is believed that most of the animal phyla in existence today had their origins during this time, often referred to as the Cambrian explosion.

First Land Plants

425 BCE

The earliest evidence of land plants consists of fossilized spores and pollen grains dating back 470 million years. Vascular plants evolved about 50 million years later. Cooksonia is a notable fossil that represents the transition to vascular plants. By the end of the Silurian Period, 420 million years ago, there was an increased diversity of plants and ecosystems on land.

Dinosaurs

155 BCE

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.