Widespread mixing and burial of Earth's Hadean crust by asteroid impacts

The history of the Hadean Earth (∼4.0-4.5 billion years ago) is poorly understood because few known rocks are older than ∼3.8 billion years old. The main constraints from this era come from ancient submillimetre zircon grains. Some of these zircons date back to ∼4.4 billion years ago when the Moon, and presumably the Earth, was being pummelled by an enormous flux of extraterrestrial bodies. The magnitude and exact timing of these early terrestrial impacts, and their effects on crustal growth and evolution, are unknown. Here we provide a new bombardment model of the Hadean Earth that has been calibrated using existing lunar and terrestrial data. We find that the surface of the Hadean Earth was widely reprocessed by impacts through mixing and burial by impact-generated melt. This model may explain the age distribution of Hadean zircons and the absence of early terrestrial rocks. Existing oceans would have repeatedly boiled away into steam atmospheres as a result of large collisions as late as about 4 billion years ago.

Lunar and terrestrial planet formation in the Grand Tack scenario

We present conclusions from a large number of N-body simulations of the giant impact phase of terrestrial planet formation. We focus on new results obtained from the recently proposed Grand Tack model, which couples the gas-driven migration of giant planets to the accretion of the terrestrial planets. The giant impact phase follows the oligarchic growth phase, which builds a bi-modal mass distribution within the disc of embryos and planetesimals. By varying the ratio of the total mass in the embryo population to the total mass in the planetesimal population and the mass of the individual embryos, we explore how different disc conditions control the final planets. The total mass ratio of embryos to planetesimals controls the timing of the last giant (Moon-forming) impact and its violence. The initial embryo mass sets the size of the lunar impactor and the growth rate of Mars. After comparing our simulated outcomes with the actual orbits of the terrestrial planets (angular momentum deficit, mass concentration) and taking into account independent geochemical constraints on the mass accreted by the Earth after the Moon-forming event and on the time scale for the growth of Mars, we conclude that the protoplanetary disc at the beginning of the giant impact phase must have had most of its mass in Mars-sized embryos and only a small fraction of the total disc mass in the planetesimal population. From this, we infer that the Moon-forming event occurred between approximately 60 and approximately 130 Myr after the formation of the first solids and was caused most likely by an object with a mass similar to that of Mars.

Chaotic capture of Jupiter's Trojan asteroids in the early Solar System

Jupiter's Trojans are asteroids that follow essentially the same orbit as Jupiter, but lead or trail the planet by an angular distance of approximately 60 degrees (co-orbital motion). They are hypothesized to be planetesimals that formed near Jupiter and were captured onto their current orbits while Jupiter was growing, possibly with the help of gas drag and/or collisions. This idea, however, cannot explain some basic properties of the Trojan population, in particular its broad orbital inclination distribution, which ranges up to approximately 40 degrees (ref. 8). Here we show that the Trojans could have formed in more distant regions and been subsequently captured into co-orbital motion with Jupiter during the time when the giant planets migrated by removing neighbouring planetesimals. The capture was possible during a short period of time, just after Jupiter and Saturn crossed their mutual 1:2 resonance, when the dynamics of the Trojan region were completely chaotic. Our simulations of this process satisfactorily reproduce the orbital distribution of the Trojans and their total mass.

Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets

The petrology record on the Moon suggests that a cataclysmic spike in the cratering rate occurred approximately 700 million years after the planets formed; this event is known as the Late Heavy Bombardment (LHB). Planetary formation theories cannot naturally account for an intense period of planetesimal bombardment so late in Solar System history. Several models have been proposed to explain a late impact spike, but none of them has been set within a self-consistent framework of Solar System evolution. Here we propose that the LHB was triggered by the rapid migration of the giant planets, which occurred after a long quiescent period. During this burst of migration, the planetesimal disk outside the orbits of the planets was destabilized, causing a sudden massive delivery of planetesimals to the inner Solar System. The asteroid belt was also strongly perturbed, with these objects supplying a significant fraction of the LHB impactors in accordance with recent geochemical evidence. Our model not only naturally explains the LHB, but also reproduces the observational constraints of the outer Solar System.

Origin of the orbital architecture of the giant planets of the Solar System

Planetary formation theories suggest that the giant planets formed on circular and coplanar orbits. The eccentricities of Jupiter, Saturn and Uranus, however, reach values of 6 per cent, 9 per cent and 8 per cent, respectively. In addition, the inclinations of the orbital planes of Saturn, Uranus and Neptune take maximum values of approximately 2 degrees with respect to the mean orbital plane of Jupiter. Existing models for the excitation of the eccentricity of extrasolar giant planets have not been successfully applied to the Solar System. Here we show that a planetary system with initial quasi-circular, coplanar orbits would have evolved to the current orbital configuration, provided that Jupiter and Saturn crossed their 1:2 orbital resonance. We show that this resonance crossing could have occurred as the giant planets migrated owing to their interaction with a disk of planetesimals. Our model reproduces all the important characteristics of the giant planets' orbits, namely their final semimajor axes, eccentricities and mutual inclinations.

Dynamical spreading of asteroid families by the Yarkovsky effect

The orbital distributions of prominent asteroid families are thought to be direct by-products of catastrophic disruption events among diameter D greater, similar 100 kilometer bodies. Ejection velocities derived from studying observed families, however, are surprisingly high compared with results from impact experiments and simulations. One way to resolve this apparent contradiction is by assuming that D less, similar 20 kilometer family members, since their formation, have undergone semimajor axis drift by the thermal force called the Yarkovsky effect. Interactions between drifting family members and resonances can also produce unique eccentricity and/or inclination changes. Together, these outcomes help explain (i) why families are sharply bounded by nearby Kirkwood gaps, (ii) why some families have asymmetric shapes, and (iii) the curious presence of family members on short-lived orbits.

Understanding the distribution of near-earth asteroids

We have deduced the orbital and size distributions of the near-Earth asteroids (NEAs) by (i) numerically integrating NEAs from their source regions to their observed orbits, (ii) estimating the observational biases and size distribution associated with asteroids on those orbits, and (iii) creating a model population that can be fit to the known NEAs. We predict that there are approximately 900 NEAs with absolute magnitude less than 18 (that is, kilometer-sized), of which 29, 65, and 6% reside on Amor, Apollo, and Aten orbits, respectively. These results suggest that roughly 40% of the kilometer-sized NEAs have been found. The remainder, on highly eccentric and inclined orbits, are more difficult to detect.

Origin of multikilometer earth- and mars-crossing asteroids: A quantitative simulation

Orbital dynamic simulations show that many asteroids in the main asteroid belt are driven toward Mars-crossing orbits by numerous weak mean motion resonances, which slowly increase the orbital ellipticity of the asteroids. In addition, half of the Mars-crossing asteroids (MCAs) transition to Earth-crossing asteroids (ECAs) in less than 20 million years. This scenario quantitatively explains the observed number of large ECAs and MCAs.

[Bilateral thrombosis of a femoral pseudoaneurysm]

One case has been described of acute thrombosis of bilateral femoral anastomotic pseudoaneurysm. The clinical finding of bilateral acute ischemia of the lower limbs required urgent surgical treatment. The operative technique consisted of excision of anastomotic aneurysms and replacement by a new segment of prosthesis with an end-to-end anastomosis to the deep femoral artery. Pathogenesis of the pseudoaneurysms at the femoral anastomosis generally recognized numerous factors such as mechanical, graft or suture defects, hypertension, wound complications. Recognition of femoral anastomotic aneurysms is usually simple, when a pulsative mass is noted. In such a case (reported) of thrombosis of bilateral femoral pseudoaneurysms, preoperative diagnosis was more difficult. Anastomotic aneurysms of little size that occur later after original intervention require observation by echography and angiodinography. When rapid enlargement arises, urgent surgical treatment is required, before rupture or thrombosis. The surgical intervention consists of excision of the anastomotic aneurysm and replacement by a new segment of prosthesis between the prosthesis and the common or deep femoral artery. If the reconstruction at the level of femoral artery is not possible, the anastomosis is performed more distally, at the level of popliteal artery. The results are affected by the degree of urgency of surgery, with significant difference in favour of the patients Who underwent elective procedures.

[Aneurysm of the iliac artery]

The authors consider isolated iliac artery aneurysms. While the incidence of isolated iliac lesion is, as literature reports, quite low, it rises up to 20% when associated with aortic lesions. The clinical findings are often characterized by effects of compression on the intrapelvic structures, by neurological symptoms and decreased venous flow. Diagnosis is based on ecography, CT and angiography for the definition of side and extension of the aneurysmatic lesion. From the technical point of view, the surgical approach is based on the dimensions of aneurysm and its mono- or bilateral extension. The most common approach in case of bilateral aneurysms or aorto-iliac lesions is transperitoneal, while it's limited to extraperitoneal way, when isolated iliac lesion. If the aneurysm involves the hypogastric artery, mostly when bilateral, the risk of bowel ischemic complications becomes more significative.

[Emergency surgery in patients over eighty]

The authors describe a series of 139 over-eighty patients (M = 53, F = 86), who underwent emergency surgery between 1-1-1987 and 30-6-1993. They consider diagnosis, copathology, type of surgical procedures, postoperative complications and final results. In this series they study 73 large bowel obstruction and 48 peritonitis. They notice important copathologies in 78% of patients, in particular cardiovascular diseases. They performed 74 mayor surgical procedures with 48% of postoperative complications and exitus in 24% of cases, due overall to exacerbation of coexisting diseases. The authors underline the direct between mortality rate and number of copathologies, and analyze the basic rules to follow in surgical indications and during the postoperative period.

[Perforated colonic diverticulitis. Surgical technique]

Emergency surgery is required for performed colonic diverticulitis. Surgical indications are not uniform in literature. In the experience of the authors the operations have been performed in the case of peritonitis subsequent to the perforation or in the case of failure of the conservative treatment. Twenty-four patients underwent surgical intervention because of diffuse (17 cases) or localized peritonitis (7 cases). Exitus were related to cardiovascular complications in patients over seventy. Postoperative results are related to the age, the general conditions of the patient and to the intraoperative finding, of localized or generalized peritonitis. Operations may be divided into two groups: conservative procedures or primary resections. In the first one it is possible to suture the colonic wall without resection; in the second one the intraoperative finding or the extensive necrotic lesions indicates colonic resection or exteriorization. The surgical treatment adopted is correlated both to the age and cardiorespiratory conditions and to the other associated diseases.

[Caustics-induced lesions of the gastrointestinal tract]

Ingestion of a corrosive agent results in a life-threatening clinical condition that requires emergency intensive care and often surgical intervention. Treatment is multifactorial and varies with the extent and depth of the injury. We report a case of a young 24-year-old man with accidental ingestion of sulphonic acid. After 1 month he developed a progressive dysphagia. Early endoscopic examination showed grade III injury to both the esophagus and stomach with severe and undilatable stricture of the antrum. Therapy included total parenteral nutrition and antibiotics. Repeat endoscopic examinations on days 30 and 40 showed progressive healing of the esophageal injuries, but confirmed a complete antral stenosis. After two months a large antecolic jejuno-gastroplasty was performed on the anterior wall of the stomach. The postoperative course was regular, and endoscopic examination showed complete healing of the injuries.

[Arteriovenous fistula of the left renal peduncle after nephrectomy. A clinical case]

The Authors report a case of arterio-venous fistula of the left renal pedicle, twenty six years after nephrectomy. The diagnosis was made by clinical signs and confirmed by angiography. Treatment was surgical with complete removal of the fistula.

[Thrombectomy of the infra- and suprarenal cava to prevent pulmonary embolism in the presence of deep venous thrombosis. Personal experience with 11 surgically-treated cases]

DVT is a fairly frequent event and often fails to be recognised. Its main complication, pulmonary embolism, is the third cause of death in Italy with more than 70,000 deaths per annum. In the presence of infra- and suprarenal floating thrombi, cases in which the application of neither intraluminal nor extraluminal filters is indicated, the treatment of choice is thrombectomy with direct surgical access to the cava. Personal experience of 11 patients operated in the past 16 months with excellent surgical success is analysed. The indications and surgical techniques adopted are described.

[Use of a new anti-inflammatory drug in the treatment of varicophlebitis of the lower limbs]

The paper reports the results obtained in 20 patients affected by varicophlebitis of the lower limbs following the oral administration of an anti-inflammatory substance. Results were compared with findings in single-blind study performed in a group of 20 patients treated with placebo. The evaluation of residual signs and symptoms and the control of recanalization of venous collectors using Doppler tests revealed a difference between the two groups in favour of the patients treated with the anti-inflammatory agent, although this was not statistically significant. The use of the drug was considered useful as a support to conservative varicophlebitis therapy with the aim of accelerating the resolution of the inflamed condition and thus reducing the functional disability of the limb.

Acute renal failure due to acute bilateral renal artery thrombosis: successful surgical revascularization after prolonged anuria

Acute bilateral renal artery thrombosis is a rare but surgically correctable cause of acute renal failure. A middle-aged woman with acute renal failure and anuria due to atherosclerotic occlusion of the abdominal aorta and both renal arteries was surgically treated 42 days after the onset of anuria. Revascularization resulted in the reversal of renal failure and complete recovery of renal function in spite of prolonged anuria. An aggressive diagnostic and therapeutic approach is important whenever this condition is suspected.

[Protection systems of erythrocytes during intraoperative autotransfusion. Experience with the use of S-adenosyl-L-methionine]

An experiment lasting 2 years in more than 200 patients in single blind conditions (S-Adenosyl-L-Methionine vs placebo) aimed to improve protection of red cells during intraoperative autotransfusion. The two groups are analysed and, on the basis of objective hematochemical data it is concluded that in patients treated with the pharmacological support erythrocyte membrane stability is good.

[Aneurysm of the popliteal artery: clinical aspects and therapy]

Experience of the operative treatment of 45 popliteal aneurysms in 41 patients is reported. The importance of immediate surgical reconstruction whenever a popliteal artery aneurysm has been detected is stressed. In fact, the patency rate of the arterial substitutes which are utilised in the reconstructive technique, and therefore the fate of the affected limbs, is chiefly based on the presence of a sufficient run off. Ischaemic complication due to peripheral embolization or sudden thrombosis of the aneurysmatic sac is very often followed by the irreversible closure not only of the tibioperoneal arteries but also of most collateral vessels.

[Surgical tactics in the treatment of thyroid nodular pathology]

The thyroid nodules represent the most frequent endocrinopathy, because clinically palpable nodules are detectable in 4-5% of the general population. Such pathological condition includes adenomas, carcinoma, intraglandular haematomas or cysts, focal thyroiditis, etc. Fine-needle aspiration cytology allows a correct diagnosis in about 90% of the cases, distinguishing focal thyroiditis from nodular goiter or thyroid malignancies. The new instrumental and cytological studies make the choice for surgical interventions more selective. At the Institution of General and Cardiovascular Surgery, University of Milan, 597 patients underwent surgery from 1966 to January 1988. The observed nodular (toxic or non toxic) thyropathies were 498 (83.4%). Cold nodules represented about a third (34%) of the nodular thyropathies. Thyroid carcinomas were 33 (5.6%). This study is aimed to analyze our surgical attitude with respect to nodular thyropathies, the surgical procedures adopted and the observed complications.

[Cervico-mediastinal goiter]

The descent of a cervical goiter below the plain of the thoracic inlet to become substernal in location, is fairly rare, but not exceptional, with an incidence, derived from several large series of operated patients, ranging from 1.7% to 13.1%. The importance of this particular location of the goiter is chiefly due to the fact that the thyroid is growing in a limited space with many surrounding structures, that unavoidably, sooner or later, will be compressed or strained. This provokes respiratory symptoms (such as cough, dyspnea, stridor) or difficulty in swallowing or determines a superior vena cava syndrome with venous stasis in the neck and in the upper thorax, and with facial oedema. The substernal location, that already constitutes a complication of the basic thyropathy, is further aggravated by the incidental malignant transformation of the substernal goiter or by the development of a thyrotoxicosis due to hyper-functioning intra-thoracic thyroid tissue. For all these reasons the presence of a substernal goiter represents in and of itself a precise indication for a surgical treatment. This study is aimed at examining the series of 19 substernal goiters observed at the Institution of General and Cardiovascular Surgery, University of Milan, from 1967 to 1987, particularly analyzing the progresses in the diagnostic procedures, the adopted surgical therapy and the observed complications.

[Loco-regional complications in the surgery of the subclavian artery]

Surgical treatment of subclavian artery atherosclerotic lesions has prophylactic significance in the evolution of cerebrovascular insufficiency. Local complications during interventions on subclavian artery are incidentally more significant than cerebral ischemic complications. Among local complications we reported 2 cases of phrenic nerve involvement and 1 case of thoracic duct lesion in a series of 86 operated patients. We never found cerebral ischemic complications in the surgery of subclavian artery atherosclerotic lesions.

[Role of anterior scalene muscle hypertrophy in thoracic outlet syndrome]

A case of hypertrophic anterior scalene muscle surgically treated is reported. The patient suffered from upper limb intermittent claudication at any sustained upper extremity activity such as lifting a weight or opening and closing the hand with the arm abducted. Doppler and angiographic study showed significant compression of subclavian artery with hyperabduction and Adson manoeuver. Simple anterior scalenotomy was followed by prompt recovery of symptoms. The results of scalenotomy and other surgical approaches to thoracic outlet syndrome are reviewed in the literature. The most common anomalies of anterior scalene muscle in the TOS are also described. Doppler and arteriographic study in different functional positions are necessary in the evaluation of subclavian artery compression by osseous or muscular structures. In the reported case scalenotomy was at least as effective as 1st rib resection.

[Complete cervical rib. Possible neurovascular implications of the upper limb]

The thoracic outlet syndrome (TOS) is caused by compression of the brachial plexus or subclavian artery or vein in the region of the neck and shoulder girdle. The neurovascular bundle may be compressed at multiple sites: costoclavicular space, interscalene triangle, insertion of the pectoralis minor into the coracoid process. More than 90% of the patients present with neurologic symptoms: pain, paraesthesias or arm and hand weakness and 10% also have vascular problems. The diagnosis of TOS is always difficult and depends on careful clinical study of patients. For the neurological type of TOS, electromyograms, arteriograms and venograms are not helpful. The value of Doppler study and of arteriography is demonstrated in the present case of a woman with a five month history of pain and paraesthesias of the arm and hand, who shoved sudden occlusion of left humeral artery. Roentgenograms showed the presence of a well developed left cervical rib. Doppler study and arteriography showed the compression of subclavian artery with the arm abduction manoeuver. After first rib resection and humeral artery thrombectomy there was a complete return of humeral artery flow and of all neurologic functions. Thus the role of first cervical rib or other bone and muscular structures must be emphasyzed both in the brachial and in the subclavian artery or vein compression. Embolization of the axillary or humeral artery should be corrected as soon as possible when the cervical rib is corrected.

[Pseudoaneurysm of the subclavian artery. Case reports]

Five patients suffering from subclavian artery false aneurysms underwent surgery in the last 6 years at the Institute of General and Cardiovascular Surgery University of Milan. The management was considerably different from the treatment of atherosclerotic lesions of this artery, because of the various nature of such traumatic lesion and the variable (stable or unstable) hemodynamic conditions of the patients. Arteriography was extremely useful in the evaluation of site and extension of pseudoaneurysms. When pseudoaneurysm was in the left side (in one case), supraclavicular incision and posterolateral thoracotomy were adopted to allow the control of both proximal and distal portion of subclavian artery. When the pseudoaneurysm was in the right side (in 3 cases) a median sternotomy with extension of the soft tissue incision into the right side of the neck provided the exposure of the proximal and distal right subclavian artery. In the last case, proximal infected false aneurysm (after right axillo-femoral bypass graft) was removed and substituted by contralateral axillo-bifemoral bypass.

[Role of conservative therapy and surgical treatment in disease caused by gastroesophageal reflux]

A series of 82 subjects affected with reflux esophagitis is presented. Gastroesophageal reflux and peptic esophagitis were discovered and staged by contrast meal and endoscopy with biopsy. All patients underwent medical therapy based on drugs affecting gastroesophageal motility and acidity of gastric content: this therapy was administered for three months, then was performed a control endoscopic examination. Endoscopic recovery of esophagitis allowed a long term maintenance therapy, endoscopically controlled every year. When esophagitis persisted, cycles of medical attack therapy, were repeated. surgical operation was performed in 15 cases in which either three cycles of medical therapy failed to improve esophageal lesions, or when endoscopy showed worsening esophagitis.

[Tumors of the upper excretory tract. Cases contribution and review of the literature]

Authors reviewed 11 cases of urothelial tumors of the upper urinary tract. Clinical history, diagnostic procedures and surgical treatment of 8 patients with tumor in the renal pelvis and of 3 patients with ureteral tumor are described. The aspecificity of clinical finding and the possibility of different urinary tract affections may be responsible of many difficulties in doing early diagnosis using routinary instrumental investigations. Nephroureterectomy is most frequently performed as surgical treatment. The results are correlated with the stage of infiltration of surrounding tissues by tumor. It is necessary an early clinical study of the patients with signs or symptoms referring to urinary tract (hematuria, abdominal pain) using excretory urogram, cystoscopy and urinary cytology in order to lower the delay of surgical procedure after the evidence of clinical finding.

Surgical treatment of thoracic aortic aneurysms. Personal experience

A series of 262 observed cases of aneurysm of the thoracic aorta is examined in which 216 cases of surgical correction were performed between 1974 and 1987. Dissecting aneurysms and post-traumatic pseudoaneurysms, although of different aetiology and morbid anatomy, are also included since the surgical technique adopted is similar in all groups. Clinically different aspects of acute and chronic lesions are analyzed. Of all preoperative examinations, angiography is preferred as it gives the most precise definition of the aortic lesion. This is especially necessary in the case of acute dissection or rupture of thoracic aorta although the role of CAT scan is becoming progressively more important. In cases of aortic dissection with massive aortic valve insufficiency, the substitution of the ascending aorta and aortic valve with reimplantation of coronary arteries, in accordance with Bentall's technique is also indicated. The improvement in surgical results is emphasized, since surgical mortality has decreased from 30.6% to 22% in the last eight years. This is due to improvement in surgical technique, to extra corporeal circulation and myocardial protection.

Acute ruptures of the thoracic aorta. Personal experience

The statistical incidence, etiopathogenesis, diagnostics and surgical treatment of acute ruptures of the thoracic aorta are described. A personal series of 7 cases is reported; surgical techniques, benefits and risks of extracorporeal circulation during surgical treatments are analysed and discussed.