Massive volcanism in Siberia kickstarted the end-Permian extinction around 250 million years ago, wiping out more than 90 per cent of marine species and two-thirds of vertebrates.

Key points: Since the Industrial Revolution, humans have released more CO2 than the Chicxulub impactor, which caused 100,000 years of global warming

Since the Industrial Revolution, humans have released more CO2 than the Chicxulub impactor, which caused 100,000 years of global warming Just one fifth of 1 per cent of the earth's carbon is above the surface

Just one fifth of 1 per cent of the earth's carbon is above the surface Burning fossil fuels is undoing aeons of natural carbon sequestration

A huge asteroid pounding into Earth killed off the dinosaurs.

Compared to these events, it might be difficult to imagine how we little humans could affect the planet's weather systems.

But researchers have calculated that we are now pumping out between 40 and 100 times more CO2 than all the volcanoes on Earth.

Or another way to look at it: if we suddenly multiplied the number of active volcanoes on the planet by between 40 and 100, that's the scale of our influence, via CO2, on the atmosphere.

The week before last, the Deep Carbon Observatory published the findings of a 10-year research project in the journal Elements, which aimed to work out how much carbon is contained on Earth and where it's stored.

By doing so, they also aimed to get a scale of what effect humans are having on the Earth's carbon cycle.

And some of their results are telling.

The carbon we don't see

As life developed on Earth, carbon dioxide was sucked from the atmosphere and buried underground. ( Matt Neal )

While we mostly hear about carbon dioxide in the atmosphere, that's merely a tiny fraction of how much carbon is stored on the Earth.

In fact, all the carbon and carbon dioxide above the surface — in the oceans, forests, soils and atmosphere — makes up just 0.2 per cent of all the carbon on the planet, according to the research.

The rest of the total 1.85 billion gigatonnes of carbon on Earth is below the surface, with nearly two-thirds of all the Earth's carbon stored deep in our planet's dense core.

But in the early days of our Earth, things were very different.

The early atmosphere — by today's measure — was soaked in carbon dioxide.

That all began to change when life emerged on the surface, according to petrology expert and lead author Balz Kamber from Queensland University of Technology (QUT).

"CO2 levels were very high on the early Earth," Professor Kamber said.

"But the [appearance] of plants had a major effect. The big thing was [that they] stored this plant carbon away as coal and gas and oil."

Over millions of years, plants drew down carbon dioxide from the atmosphere. When those plants were buried — say in the case of mangroves being buried under mud — they couldn't break down and so their carbon wasn't released back into the air.

Underground, that buried carbon formed oil, coal and gas.

And over aeons, these processes tipped the carbon balance away from the atmosphere, resulting in a crust and mantle enriched with carbon and an atmosphere relatively low in CO2.

Aeons of carbon sequestration tipped the CO2 balance

Carbon sequestration happens when carbon-containing materials like timber are buried where oxygen can't get to them. ( ABC Open contributor Ally.C )

In the oceans, animals that built themselves calcium-carbonate shells had a similar effect to vegetation.

Those animals sunk to the ocean floor when they died, and were buried.

Over time, those layers of shells were compacted and became carbon-rich limestone deposits.

Today, the researchers estimate there is about 315 million gigatonnes of carbon stored in the Earth's crust and upper mantle.

And there are broadly two carbon cycles, moving this carbon between the atmosphere and the Earth.

Firstly, the rapid carbon cycle involves the release and absorption of CO2 from the oceans and land. The researchers estimate there is about 43,500 billion tonnes of carbon in that system, and it has until recently been roughly in balance.

Second, we have the slow carbon cycle which involves the recycling of land back into the mantle via plate tectonics, and the outgassing of carbon dioxide via volcanoes and vents.

Again, researchers say that has been roughly in balance for the last billion years or so, punctuated by a few dramatic upheavals.

Asteroids hitting limestone vaporise shells

All of Earth's volcanic emissions are dwarfed by the CO2 produced by humans. ( Supplied: Yves Moussallam, Lamont Doherty Earth Observatory )

There are only three major things today that can cause such upheavals.

The first is an asteroid.

While we might think that the direct impact of a massive meteorite on the planet would be enough to wipe us all out, there actually needs to be some pretty unique circumstances for a space visitor to really upset the carbon cycle.

"Just hitting the Earth isn't enough. It's when meteorites hit limestone that a lot of carbon is released into the atmosphere," Professor Kamber said.

"There's only two [meteorites] that we know of, really big ones that hit limestone, and one is the one that everyone knows about that hit Yucatan in Mexico."

Meteorite impacts disrupt the carbon cycle when they strike limestone deposits. ( ABC Kimberley: Matthew Moreton-Deakin )

The meteorite that hit Yucatan, at a site we know today as the Chicxulub Crater, is thought to have wiped out the dinosaurs.

After that impact, global cooling was caused by the release of sulfate into the atmosphere.

Sulfate blocked the sun's incoming rays, disrupted photosynthesis and wiped out the food sources of most animals on the planet.

But sulfate is short-lived, and was quickly washed from the atmosphere as acid rain.

CO2 on the other hand, isn't.

The elevated carbon-dioxide levels left in the atmosphere after the Yucatan impact raised global temperatures by up to 5 degrees Celsius for around 100,000 years, according to research in Science.

Volcanoes dwarfing Krakatoa

The second thing that can upset the Earth's carbon cycle is volcanoes.

One of the biggest volcanic events in geological history happened just over 250 million years ago, in the Siberian Traps.

It's thought that there was enough lava from these eruptions — which lasted tens of thousands of years — to cover the United States a kilometre deep.

These eruptions spewed masses of greenhouse gases into the atmosphere, temperatures were up to 10C higher than they are today and the oceans became highly acidic.

Few species on the planet escaped unscathed.

But modern humans have never experienced major planet-disrupting volcanoes or meteorites.

"The effect of Krakatoa can be seen in tree rings — cooling — and that affected crop harvests as well," Professor Kamber said.

"[But] on a global scale in the longer term, even Krakatoa was still quite a small eruption."

Then there's us

People have released more CO2 than the meteorite impact that caused 100,000 years of global warming. ( AP: Amel Emric )

Professor Kamber's contribution to the Deep Carbon Observatory project was to analyse past disruptions to the carbon cycle and compare them to what we are doing today.

"Then there's us — we are of the same magnitude in terms of the [meteorite] impact," Professor Kamber said.

"[The Yucatan meteorite impact] released let's say a comparable amount of carbon into the atmosphere as we have already released since the Industrial Revolution."

By digging up and burning carbon from the Earth's crust as fossil fuels, we're undoing aeons of carbon sequestration.

In the process, we're shifting the carbon balance away from our crust and back into the atmosphere.

From 280 parts per million at the Industrial Revolution, atmospheric CO2 levels are now above 415 parts per million.

As we continue to burn fossil fuels and forests, we're sliding the scales of the Earth's carbon balance further than the meteorite that caused 100,000 years of global warming.