History of Life on Earth by Lochana Sreeram

sreeramlochana8023 — 2023-12-12 20:00:14 UTC

The Earth formed 4.6 BYA. The crusts formed by materials of different densities separating. This consists of the solid core, liquid core, mantle, lithosphere, continental crust, and oceanic crust.

This was the start of the formation of the solar system and the origin of Earth.

This was the start of the Precambrian Era and the Hadean Eon.

sreeramlochana8023 — 2023-12-12 20:08:50 UTC

4.5 BYA, Theia struck Earth, and was vaporized and blasted into space, forming the moon.

4.4 BYA Earth had cooled and now had water. There are theories that earth always had water in the rocks, or that it got it from impactors (comets & meteorites).

sreeramlochana8023 — 2023-12-12 20:12:23 UTC

4.2 BYA, It is presumed this is when the first large oceans formed.

4.1 BYA Flecks of carbon found imply the existence of life during this time, though evidence is minimal at best.

sreeramlochana8023 — 2023-12-12 20:21:15 UTC

3.9 BYA, It is assumed that the Last Universal Common Ancestor (LUCA), is presumed alive at this time according to certain genetic evidence. It gave rise to two single-cell groups of life--bacteria and archaea, although we don't know when or how this split happened.

This was the end of the Hadean Eon and start of the Archean Eon.

sreeramlochana8023 — 2023-12-12 20:23:07 UTC

3.7 BYA, there is a chance we have found rocks of fossilized microorganisms from this time. There is also a chance the first large land masses emerge at this time from the ocean, affecting tectonic plates.

sreeramlochana8023 — 2023-12-12 20:27:21 UTC

3.5 BYA, the oldest confirmed fossils of single-celled organisms are from this time. The ecosystem is complex and thriving, which implies that life has been around a while and is well established.

sreeramlochana8023 — 2023-12-13 02:29:31 UTC

3.4 BYA, some bacteria started performing photosynthesis, the earliest we have evidence of photosynthesis. This is a different type of photosynthesis called anoxygenic photosynthesis where oxygen isn't released as a waste product.

sreeramlochana8023 — 2023-12-13 02:31:17 UTC

3.2 BYA, We find fossilized microbes from this time, confirming that there was life on land at this point in time.

sreeramlochana8023 — 2023-12-13 02:32:57 UTC

3 BYA, While we know viruses were present at least from this time, it might have been as old as life.

sreeramlochana8023 — 2023-12-13 03:20:25 UTC

2.7 BYA, the first cyanobacteria appeared.

2.5 to 2.2 BYA, some cyanobacteria develop a new type of photosynthesis where they release oxygen, the same kind of photosynthesis we know now. This excess makes the iron in the ocean's 'rust' and sink all down to the floor of the sea. There is a chance this excess of oxygen also caused a mass extinction with microbes, and because of natural selection, today most animals breathe oxygen.

2.4 to 2.1 BYA, the Huronian ice age begins

This was the end of the Archean Eon and the start of the Proterozoic Eon.

sreeramlochana8023 — 2023-12-13 03:23:16 UTC

2.3 BYA, A lack of volcanic activity caused the first instance of a snowball earth. The eventual melted ice led to higher levels of oxygen in the atmosphere.

sreeramlochana8023 — 2023-12-13 04:19:00 UTC

2 BYA, This is when eukaryotic cells came into being, at the very least our earliest non-disputed fossil of a eukaryotic cell is found from this time.

This is also when the oxygen in the atmosphere reached dangerous levels, which led to molecular oxygen combining with a single oxygen atom from the Sun's UV Rays to form ozone (O₃), thus forming what we call today as 'the ozone layer'.

sreeramlochana8023 — 2023-12-13 04:21:23 UTC

1.6 BYA, Fossils from this time period were found, the earliest fossil of complex life found. This suggests some eukaryotes had evolved into multicellular, large organisms.

sreeramlochana8023 — 2023-12-13 04:23:59 UTC

1.4 BYA, The eukaryotes split into three separate lineages that evolved separately. These are the ancestors of modern plants, fungi, and animals.

1.3 BYA, the first land fungi appeared.

sreeramlochana8023 — 2023-12-13 04:32:25 UTC

1 BYA, multicellular organisms appear to have distinct cell types.

890 MYA, the first recognizable animals may have evolved from this time.

sreeramlochana8023 — 2023-12-13 04:46:35 UTC

850 to 635 MYA, The Cryogenian Ice Age happens.

800 MYA, Fungi evolved into multicellular body parts. Early multicellular organisms split into sponges and non-sponges, although there is some debate about the idea.

717 to 636 MYA, there is another snowball Earth.

700 MYA, this is around when the first land plants appeared, though fungi have been around much longer.

630 MYA, some animals evolve bilateral symmetry.

sreeramlochana8023 — 2023-12-13 04:52:23 UTC

590 MYA, The animals with bilateral symmetry divide into protostomes and deuterostomes, the former without vertebrates and the latter with plus the Ambulacraria (before they eventually break away).

570 MYA, when the first invertebrates appeared.

541 MYA, This was the end of the and the Proterozoic Eon, which also meant it was the end of the Precambrian Era, as the Proterozoic Eon is the last eon in the Precambrian Era. This was also the start of the Phanerozoic Eon, which is still going on to this day.

500 MYA, when the first vertebrates appeared.

489 MYA, The Great Ordovician Biodiversification Event caused a big diversity of life.

Paleozoic Era, 541 MYA - 252 MYA

Cambrian Period, 541 MYA - 485 MYA

Ordovician Period, 485 MYA - 444 MYA

Silurian Period, 444 MYA - 419 MYA

sreeramlochana8023 — 2023-12-13 05:33:20 UTC

460 to 430 MYA, the Andean-Saharan Ice Age Happens.

444 MYA, End Ordovician mass extinction occurs.

423 MYA, the first land animals appeared.

400 MYA, Insects may start appearing in the fossil record around this time.

372 to 359 MYA, The Late Devonian mass extinction occurs.

368 MYA, the earliest amphibian we now appeared around this time.

315 MYA, the earliest reptiles evolved from a sauropsida ancestor.

260 MYA, we had a group of therapsids called the cynodonts that were our first mammals.

Devonian Period, 419 MYA - 359 MYA

Mississippian Period, 359 MYA - 323 MYA

Pennsylvanian Period, 323 MYA - 299 MYA

Permian Period, 299 MYA - 252 MYA

sreeramlochana8023 — 2023-12-13 05:38:49 UTC

250 MYA, The Permian period ends with the greatest mass extinction in Earth’s history. It fundamentally changed ecosystems to this day. This is around when dinosaurs came to be.

233 MYA, proto-mammals may have evolved warm-bloodedness around this time.

210 MYA, there is miniscule evidence suggesting early dinosaurs evolved in this time.

205 MYA, The first mammals came to be.

200 MYA, the triassic period ends along with another mass extinction.

150 MYA, Birds came to be as far as we know, though this could be disputed as the time is not set.

130 MYA, It is thought this is when flowering plants came to be.

Triassic Period, 252 MYA - 201 MYA

Jurassic Period, 201 MYA - 145 MYA

Cretaceous Period, 145 MYA - 66 MYA

Paleogene Period, 66 MYA - 23 MYA

sreeramlochana8023 — 2023-12-13 06:35:37 UTC

66 MYA, all dinosaurs with the exception of small forms, like birds, vanish, known as the 'end Cretaceous' extinction.

2.6 MYA to today, The Quaternary Ice Age happens.

2 MYA, this is the earliest time humans possibly could have evolved, though it could be as late as 6 MYA.

Today, all living things are currently classified into five kingdoms according to the most widely used scheme: Monera (bacteria), Protista, Fungi, Plantae, and Animalia. This coexisted with a scheme that classified life into two primary groups: the Eukaryotae (plants, animals, fungi, and protists) and the Prokaryotae (bacteria, etc.).

Mesozoic Era, 252 MYA - 66 MYA

Cenozoic Era - 66 MYA - Today

Neogene Period, 23 MYA - 1.8 MYA

Quaternary Period, 1.8 MYA - Now