When NASA’s Perseverance rover landed in Jezero Crater in 2021, its primary mission was to scour the remnants of a dried-up Martian lakebed for signs of ancient life. Scientists have been focused on the crater’s spectacular Western Delta, a fan-shaped geologic feature deposited by a river flowing into the basin billions of years ago. But now Perseverance’s ground-penetrating radar (called RIMFAX) detected what is likely another, even older river delta buried tens of meters beneath it.

“I think it’s a promising place to look for signs of biosignatures at depth,” says Emily L. Cardarelli. “Microbial life could have potentially developed in those types of environments.” Cardarelli, an astrobiologist at the University of California Los Angeles, led the team interpreting RIMFAX imagery.

Peeking underground

Perseverance’s RIMFAX, the Radar Imager for Mars Subsurface Experiment, continuously fires radar waves into the ground, acquiring soundings each time the rover traveled 10 centimeters. When these radio waves hit boundaries between different types of rock, ice, or sediment layers, some of the signal bounces back. The timing and intensity of these reflections allow scientists to construct a two-dimensional, vertical slice of the subsurface, much like a sonogram of the Martian crust.

During a campaign spanning from September 2023 to February 2024, or over 250 Martian sols, Perseverance drove across a geological zone known as the Margin unit. The Margin unit is an expansive deposit flanking the inner rim of Jezero’s inlet valley, occupying the space between the western fan deposits and the crater rim. It is rich in magnesium carbonates, which was one of the main reasons Jezero Crater has been chosen as the Perseverance’s landing site: on Earth, carbonates are exceptionally good at preserving the chemical fingerprint of life. “You can think of the Cliffs of Dover, for example, that are all carbonate—they have tons of fossils in them,” Cardarelli says.

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This is not science fiction. In remote corners of the world, geologists have found tiny relics of Earth’s very ancient surface.

I have been part of this scientific endeavour, looking at the treasure trove of information in the bedrock of the Makhonjwa Mountains in South Africa and the adjacent small kingdom of Eswatini.

These rocks reach back more than three quarters of the way through our planet’s long history of nearly 4.6 billion years. In my new book, The Oldest Rocks on Earth, I describe the graphic images “beamed back” by this geological time machine.

World of oceans

The ancient rocks reveal a world with extensive oceans and intense volcanic activity on the sea floor.

Deep beneath the crust, Earth was much hotter than today, giving rise to an unusual white-hot magma, rich in elements from its interior. Huge volumes of super-heated water continually gushed out of underwater cracks, building up chimneys of valuable metals. And life was thriving around these undersea vents.

Volcanic islands rose up from the ocean depths. These were dangerous places. Pools of hot bubbling mud dotted their shores, and clouds of volcanic ash periodically exploded from volcanic craters.

Life was already there, forming microbial mats in the sheltered nearshore waters.

Periodically, large earthquakes violently shook the bedrock, triggering submarine avalanches that cascaded down into the deep ocean, creating vast jumbles of rock on the sea floor. Giant asteroid impacts disturbed this world, but crucially, did not extinguish it.

Deep-seated forces were pushing up new land, creating the early continents.

Ocean waves moved back and forth on sandy beaches along coastlines with bays, lagoons, inlets and estuaries, with tides similar to those today.

During floods, large rivers brought muddy water from the continental interior. Farther in the distance, their headwaters drained a mountainous terrain, often enveloped in thick cloud.

It was a blue planet because, like today, the oceans scattered light in the blue part of the colour spectrum.

But the atmosphere contained a lethal cocktail of gases, including high concentrations of methane and carbon dioxide. These greenhouse gases kept the surface at the right temperature for liquid water, at a time when astrophysicists calculate the Sun was much weaker. But there was no oxygen.

The earliest life forms were anaerobic microbes, although brightly coloured – pink or purple have been proposed.

Oceania today

Oceania, in the southwestern Pacific, may illustrate best what this early world was like. Here, the ocean is peppered with volcanic islands and small continents, rocked by great earthquakes where tectonic plates rub against each other. There are even clues to how life began.

The 2022 eruption of the Hunga volcano, near Tonga, created a mushroom cloud of ash that burst out of the ocean and reached up into space with an estimated energy of a 60-megaton atomic bomb. It generated more than 200,000 lightning strikes and left behind a deep underwater crater filled with a chemical soup derived from numerous underwater hot vents.

Experiments show that lightning strikes can trigger the synthesis of basic organic molecules needed by living organisms. Millions of Hunga-like eruptions on early Earth would have created myriad opportunities to kick start the chemistry of life in underwater volcanic craters – life was born out of extreme geological violence.

Staying blue

Going back in time beyond the Makhonjwa Mountains, we still find evidence for oceans, life and, I argue, plate tectonics. Earth became blue within the first tenth of its history.

Mars and Venus may have started this way, too. But our planet uniquely lies in the so-called Goldilocks Zone, receiving just the right amount of solar energy to avoid becoming a boiling Venusian hell or freezing Martian world.

It is also big enough to have a magnetic field and pull of gravity sufficient to retain its atmosphere. And right at the start, a dramatic collision with a Mars-sized asteroid spalled off our Moon, stabilising Earth’s spin axis so that day and night were less extreme.

Finally, the biochemistry of living organisms may have played a key role in keeping Earth this way by helping the bedrock absorb greenhouse gases in the face of a steadily warming Sun.

We must not be the first to let Earth lose its distinctive life-giving blue, a colour so wonderfully referred to in the Siswati language of Eswatini as luhlata lwesibhakabhaka, literally “green like the sky”.

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For an earthquake of this size, aftershocks can continue for weeks to months or longer, but they typically will reduce in both magnitude and frequency over time.

Other examples of subduction plate boundary earthquakes include the 2011 magnitude 9.1 Tohoku-Oki Japan earthquake, and the 2004 magnitude 9.3 Sumatra-Andaman Indonesia “Boxing Day” earthquake. Both of these initiated at a relatively shallow depth and ruptured the plate boundary right to the surface.

For instance, the area has been seismically very active in recent months, and a magnitude 7.4 earthquake occurred on 20 July. How this previous activity affected the location and timing of today’s earthquake will be a crucial focus of that research.

Originating at a depth of roughly 20 kilometres, today’s powerful earthquake – among the ten strongest in recorded history and the largest worldwide since 2011 – has caused building damage and injuries in the largest nearby city, Petropavlosk-Kamchatsky, just 119 kilometres from the epicentre.

The Pacific region is highly prone to powerful earthquakes and resulting tsunamis because it’s located in the so-called Ring of Fire, a region of heightened seismic and volcanic activity. All ten most powerful earthquakes recorded in modern history were located on the Ring of Fire.

Why does Kamchatka get such strong earthquakes?

Read more:
Tsunami warnings are triggering mass evacuations across the Pacific – even though the waves look small. Here’s why

Another factor that affects the rates and sizes of subduction zone earthquakes is the speed at which the two plates are moving relative to each other.

They uplifted one side of the sea floor relative to the other, displacing the ocean above it and resulting in devastating tsunamis. In the case of the Boxing Day earthquake, the sea floor rupture happened along a length spanning roughly 1,400km.

Tsunami scientists will continue to refine their models of the tsunami’s effects as it propagates, and civil defence authorities will provide authoritative advice on the expected local effects.

Today at about 11:30am local time, a magnitude 8.8 earthquake struck off the coast of Russia’s Kamchatka Peninsula in the country’s far east.

Based on the characteristics of this plate interface, and geological records of past earthquakes, it is likely the Hikurangi subduction zone is capable of producing earthquakes at magnitude 9. It hasn’t done so in historic times, but if that happened it would produce a tsunami.

Because of the large areas of interface at plate boundaries, both in length and depth, the rupture can span large areas of the plate boundary. This results in some of the largest and potentially most damaging earthquakes on earth.

What is likely to happen next?

Immediately offshore the Kamchatka Peninsula is the Kuril-Kamchatka Trench, a tectonic plate boundary where the Pacific Plate is being thrust beneath the Okhotsk Plate.

In the case of Kamchatka, the Pacific Plate is moving at approximately 75 millimetres per year relative to the Okhotsk plate. This is a relatively high speed by tectonic standards, and causes large earthquakes to happen more frequently here than in some other subduction zones. In 1952, a magnitude 9.0 earthquake occurred in the same subduction zone, only about 30 kilometres away from today’s magnitude 8.8 earthquake.

Tsunami warnings and evacuations have reverberated through Russia, Japan and Hawaii, with advisories issued for the Philippines, Indonesia, and as far away as New Zealand and Peru.

At time of writing, approximately six hours after the earthquake struck, there have already been 35 aftershocks larger than magnitude 5.0, according to the United States Geological Survey.

Like Kamchatka and northern Japan, New Zealand also sits above a subduction zone – in fact, above two subduction zones. The larger of these, the Hikurangi subduction zone, extends offshore along the east coast of the North Island.

Aftershocks happen when stress within Earth’s crust is redistributed following the mainshock. They are often as large as one magnitude unit smaller than the mainshock. In the case of today’s earthquake, that means aftershocks larger than magnitude 7.5 are possible.

Over the coming hours, the tsunami will propagate across the Pacific, reaching Hawaii approximately six hours after the earthquake struck and continuing as far as Chile and Peru.

What are the lessons from this earthquake for other parts of the world?

The threat of a major subduction zone earthquake never goes away. Today’s earthquake in Kamchatka is an important reminder to everyone living in such earthquake-prone areas to stay safe and heed warnings from civil defence authorities.

Here’s why the underlying structure of our planet makes this part of the world so volatile.

While tectonic plates move continuously relative to one another, the interface at tectonic plates is often “stuck”. The strain related to plate motion builds up until it exceeds the strength of the plate interface, at which point it is released as a sudden rupture – an earthquake.

Fortunately, earthquakes as large as today’s occur infrequently. However, their effects locally and across the globe can be devastating.

Apart from its magnitude, several aspects of today’s Kamchatka earthquake will make it a particularly important focus of research.

Today’s earthquake also produced a tsunami, which has already affected coastal communities on the Kamchatka Peninsula, the Kurile Islands, and Hokkaido, Japan.

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