What Is the Oldest Form of Life on Earth? A Journey into Deep Time

Defining “Life”: Where Do We Even Begin?

Before jumping into ancient fossils and microscopic organisms, let’s take a step back. What even counts as life? Scientists usually agree it’s something that grows, reproduces, and responds to its environment. That narrows it down, but only a bit.

And now here’s the tricky part: when we say "oldest form of life," do we mean the first species that ever lived, or do we mean the oldest still-living type of organism? Turns out… both questions are fascinating, and the answers might surprise you.

The First Life on Earth: Microbes Rule the Timeline

Meet the anaerobic champions

The oldest known forms of life were microorganisms, specifically prokaryotes — simple, single-celled organisms without a nucleus. We're talking bacteria and archaea, and some of them didn’t even need oxygen to survive. In fact, oxygen would’ve killed them.

The earliest fossil evidence of such life dates back at least 3.5 billion years. Yep, billion with a b. These microfossils were found in ancient rock formations in Australia and South Africa, and while there’s debate around interpretation (as always in science), most researchers agree: life was already doing its thing back then.

Some scientists argue life might’ve appeared even earlier — like 4.1 billion years ago — but that’s still hotly debated. Either way, we’re talking microbial mats, stromatolites, and other squishy, gooey life forms that wouldn’t win any beauty contests but basically ruled the world.

Stromatolites: living fossils

Stromatolites are layered structures formed by cyanobacteria — a kind of photosynthetic bacteria. They’ve been around for over 3 billion years, and guess what? They still exist today in a few salty, low-competition spots like Shark Bay, Australia.

So yeah, stromatolites are kinda like the great-great-great-(repeat 10 million times)-grandparents of life as we know it.

Still Alive Today: What’s the Oldest Living Lineage?

Archaea and extremophiles

Archaea, one of the earliest life domains, still exist today and thrive in extreme environments — boiling vents, acidic lakes, deep ocean trenches. These guys laugh in the face of what we’d consider inhospitable. It’s mind-blowing that we share ancestry with something that lives near underwater volcanoes.

In a sense, archaea are the ultimate survivors — adapted to ancient Earth and still kicking it in 2025.

Cyanobacteria: oxygen-makers since forever

Cyanobacteria — also called "blue-green algae" (though they're not technically algae) — are not just ancient, they changed the planet. Around 2.4 billion years ago, they started pumping out oxygen during photosynthesis. This caused the Great Oxygenation Event, which wiped out many anaerobic organisms but paved the way for more complex life. Including us.

So, when you breathe… thank some ancient cyanobacteria.

The Debate: Is Life Older Than We Think?

Some researchers believe the building blocks of life came from space — a theory called panspermia. Wild, right? Meteorites containing organic molecules have been found, but we’ve got no direct proof that life hitched a ride.

Still, it raises a juicy point: if Earth’s first life appeared so early in its history, maybe the universe is teeming with microbes — and we’re just late to the party.

Conclusion: Life Began Small… but Mighty

The oldest form of life on Earth? It’s microscopic, ancient, and still among us. Whether you look at stromatolites, archaea, or cyanobacteria, one thing’s clear: simple life showed up early and dominated for billions of years before anything with a spine came along.

So next time you hear someone say bacteria are gross… maybe remind them they were here first. And they might be here long after we’re gone.

Is 165 cm normal for a 15 year old?

The predicted height for a female, based on your parents heights, is 155 to 165cm. Most 15 year old girls are nearly done growing. I was too. It's a very normal height for a girl.

Is 160 cm too tall for a 12 year old?

How Tall Should a 12 Year Old Be? We can only speak to national average heights here in North America, whereby, a 12 year old girl would be between 137 cm to 162 cm tall (4-1/2 to 5-1/3 feet). A 12 year old boy should be between 137 cm to 160 cm tall (4-1/2 to 5-1/4 feet).

How tall is a average 15 year old?

Average Height to Weight for Teenage Boys - 13 to 20 Years

How to get taller at 18?

Staying physically active is even more essential from childhood to grow and improve overall health. But taking it up even in adulthood can help you add a few inches to your height. Strength-building exercises, yoga, jumping rope, and biking all can help to increase your flexibility and grow a few inches taller.

Is 5.7 a good height for a 15 year old boy?

Generally speaking, the average height for 15 year olds girls is 62.9 inches (or 159.7 cm). On the other hand, teen boys at the age of 15 have a much higher average height, which is 67.0 inches (or 170.1 cm).

Can you grow between 16 and 18?

Most girls stop growing taller by age 14 or 15. However, after their early teenage growth spurt, boys continue gaining height at a gradual pace until around 18. Note that some kids will stop growing earlier and others may keep growing a year or two more.

Can you grow 1 cm after 17?

Even with a healthy diet, most people's height won't increase after age 18 to 20. The graph below shows the rate of growth from birth to age 20. As you can see, the growth lines fall to zero between ages 18 and 20 ( 7 , 8 ). The reason why your height stops increasing is your bones, specifically your growth plates.